Titan News 2017
November 22, 2017 : A New Study Reveals A Surprising Cooling Process Of A Polar Vortex On Titan
Researchers are particularly interested in the dynamics of Titan's complex atmosphere which may look like the atmosphere of the Early Earth. Like in our atmosphere, there are some seasonal phenomena in the atmosphere of Saturn's largest moon like polar cyclones or vortices, storms or cirrus-like clouds. Data obtained from the Cassini spacecraft allowed us to monitor or to analyze the evolution of Titan's meteorology from the start of the Cassini-Huygens mission inside the System of Saturn in mid-2004 to the crash of the Cassini orbiter into the Gas Giant Saturn on September 15, 2017. A new study led by Doctor Nicholas Teanby (Nick Teanby) from the University of Bristol's School of Earth Sciences, entitled « The formation and evolution of Titan's winter polar vortex » and recently unveiled in Nature Communications reveals the finding of a surprising cooling process of a polar vortex closely related to the Autumn or Winter season. The cooling process is remarkably high and may be linked to the exotic chemistry taking shape in the hazy atmosphere of the giant moon.
Titan captivates our imagination because the enigmatic moon is covered by a significant atmosphere which is completely opaque preventing us from observing the surface from outer space in the visible spectrum. The Orange Moon is mainly composed of nitrogen like the atmosphere of the Earth but oxygen, which is the second most abundant gas present in our atmosphere, is absent or quasi-absent in the Titanian atmosphere. The second most abundant gas or molecule present in Titan's atmosphere is methane. Under the action of ultraviolet light in particular, various chemical reactions take shape in the upper atmosphere of the Opaque Moon engendering new molecules, new organics, hydrocarbons or nitriles which can fall toward the surface. Titan is bigger than the small planet Mercury and unlike Mercury or Ganymede, the largest moon of Jupiter and the largest moon in the Solar System, the Orange Moon is covered by a significant atmosphere. Are there internal sources to the methane present in Titan's atmosphere ? Is the atmosphere of Titan relatively stable over time ?
The relatively recent cooling process identified in the atmosphere over the south polar region is surprising because the phenomenon is not in line with all model predictions or prevailing models. That particular cooling process doesn't correspond to the behaviour of all other known rocky planets or terrestrial planets found in our Solar System. The formation or the development of the south polar vortex was identified during the Autumn season in the southern hemisphere of the Opaque Moon. The Autumn Equinox in the southern hemisphere and the Spring Equinox in the northern hemisphere occurred in August 2009. Each season on Titan lasts approximately seven Terrestrial years and a Titanian year lasts almost 30 Terrestrial years. The polar vortex evolving at a relatively high altitude above the south polar region seems remarkably cold and at first sight, that particular phenomenon doesn't appear logical because, generally, in the Winter hemisphere of the planetary body or moon, the upper atmosphere is warm due to a compression and heating process generated by sinking air. That's what happens, for instance, in a bicyle pump where the air is being compressed and heated. The high-altitude polar vortex found over the south polar region demonstrates that reality can be more complicated than expected.
During the particularly long mission of the Cassini orbiter inside the Saturn System, corresponding to about 13 Earth years or almost half of a Titanian year, the Cassini spacecraft performed numerous flybys of the giant moon and acquired a long series of observations of the polar atmosphere on the basis of the Composite Infrared Spectrometer or CIRS instrument. The data gathered by the CIRS instrument have revealed that the anticipated polar vortex or polar hot spot in the southern hemisphere started to develop at the beginning of the harsh period of the southern hemisphere in 2009 and that the atmospheric feature progressively became a cold spot in 2012. From 2012 to late 2015, the atmospheric feature or the polar vortex appeared particularly cold with recorded temperatures as low as 120 Kelvin that is to say minus 153 degrees Celsius or minus 243 degrees Fahrenheit. However, in the most recent observations performed in 2016 and 2017, the south polar vortex had become relatively hot or warm again as initially expected.
What are the mechanisms of the significant cooling process identified above the south polar region ? The cooling process taking shape above the south polar region of Titan is not related to the presence of carbon dioxide as opposed to the atmospheric configuration of the Earth, Venus or Mars since CO2 is absent or almost absent in Titan's atmosphere. The planetologist Nicholas or Nick Teanby pointed out : « For the Earth, Venus, and Mars, the main atmospheric cooling mechanism is infrared radiation emitted by the trace gas CO2 and because CO2 has a long atmospheric lifetime it is well mixed at all atmospheric levels and is hardly affected by atmospheric circulation. » The hazy atmosphere of the Opaque Moon is rich in organics and hydrocarbons and photochemistry, related to UV radiations from the Sun in particular, plays a key role in the upper atmosphere which appears as a soup of various molecules or compounds like acetylene or hydrogen cyanide. Nick Teanby added : « However, on Titan, exotic photochemical reactions in the atmosphere produce hydrocarbons such as ethane and acetylene, and nitriles including hydrogen cyanide and cyanoacetylene, which provide the bulk of the cooling. »
The gases, compounds or molecules generated in the upper atmosphere of Saturn's largest moon under the action of solar radiations have a steep vertical gradient which implies that their abundances can radically change under the influence of small or limited vertical atmospheric circulations. As a result, the concentration of active gases engendered by the photochemical soup, over the south polar region, during the harsh period, significantly increased due to a phenomenon of polar subsidence taking shape during the harsh period, from the start of the Autumn season to the Winter season. Planetologists used data related to temperature and gas abundances captured from the Cassini orbiter, combined with a numerical radiative balance model of heating and cool rates, to demonstrate that trace gas enrichment was massive enough to engender a relatively strong cooling and particularly cold atmospheric temperatures. The cooling process identified by the team of Nick Teanby is likely to help us better understand the observations of enigmatic hydrogen cyanide ice clouds observed at a high altitude above the south polar region in 2014 with the eyes of the Cassini spacecraft.
Doctor Nicholas Teanby argued : « This effect is so far unique in the solar system and is only possible because of Titan's exotic atmospheric chemistry. » He added : « A similar effect could also be occurring in many exoplanet atmospheres having implications for cloud formation and atmospheric dynamics. » The Orange Moon has a meteorological cycle like the Earth but the meteorological cycle of Titan involves methane rather than water which appears in its solid form on the surface of Saturn's largest moon. There are lakes, seas and rivers in the high latitudes of Titan, especially in the high latitudes of the northern hemisphere. Those bodies of surface liquids are apparently related to a meteorological cycle implying evaporation processes, condensation processes with the development of cloud systems and precipitation processes like on Earth. The particular distribution of lakes, seas and rivers on Titan is really surprising and may be closely related to environmental temperatures and atmospheric phenomena. The dark areas of Titan's low latitudes are dominated by Seif dunes or linear and parallel dunes extending over long distances. Those landscape features appear to be sculpted by prevailing winds.
It must rain at low latitudes from time to time. Infrared or near-infrared views obtained in 2010, at the beginning of the Spring season in the northern hemisphere and of the Autumn season in the southern hemisphere, revealed a strong meteorological activity at low or mid-latitudes. The cloud systems may have engendered rainfall. The panoramic views acquired from the Huygens probe during its atmospheric descent had unveiled bright hills or mountains composed of dark drainage channels. The contrast between the bright hills or mountains and the relatively dark plain was quite surprising. Some viewers had thought that the dark, brown or orange plain was filled with liquids but the view of the surface after the historic touchdown of January 14, 2005 revealed a dried up stream, river or brook with eroded stones or pebbles. The most humid area on Titan, today, appears to be in the high latitudes of the northern hemisphere where major seas or lakes can be clearly identified in radar views. A giant ethane cloud engulfing the north polar region during the Winter period had been observed. Will a similar ethane cloud develop above the south polar region as the Winter season advances in the southern hemisphere ? The environment of Titan which can produce different types of organics or hydrocarbons like propylene surprises us. Despite the fact that Titan's atmosphere is heavy and opaque, there are no significant greenhouse effects as opposed to Venus for instance. Does the haze engender greenhouse effects or anti-greenhouse effects ? What is the history and the destiny of Titan's atmosphere ? Titan's atmosphere deserves our whole attention.
The image above reveals the cyclone or vortex located high above the south polar region of Saturn's largest moon. One can also notice the detached haze of Titan's upper atmosphere. The image was obtained from the ISS Narrow-Angle Camera of the Cassini spacecraft on August 20, 2013 with a spectral filter sensitive to wavelengths of near-infrared radiations centered at 889 nanometers. The cyclone or vortex developed during the Autumn season in the southern hemisphere and appeared surprisingly cold from 2012 to 2015. Image Credit: NASA/JPL-Caltech/Space Science Institute.
- To get further information on that news, go to: http://www.bristol.ac.uk/news/2017/november/titan-vortex-.html and https://www.nature.com/articles/s41467-017-01839-z.
October 27, 2017 : Is There An Intelligent Lifeform In Titan's Hypothetical Subsurface Ocean Of Liquid Water ?
Today, the Earth appears to be the only world in the Solar System to harbor an intelligent lifeform on its surface. The exploration of the Solar System has not even allowed us to identify signs of life or to collect significant clues regarding past or present lifeforms outside the Earth. The fungi, the bacteria or the archaea we know are only found on our planet. The SETI (Search for Extra-Terrestrial Intelligence) program which aims at identifying extraterrestrial radio signals emanating from elsewhere in our giant Universe is not fruitful since we haven't found anything yet regarding hypothetical intelligent civilizations located elsewhere in our Solar System, in our galaxy, the Milky Way, or in other galaxies. At first sight, we might be alone in the Solar System or even in the Universe.
Let's note however that we only have sent landers to a few worlds in our Solar System. The Moon, Venus, Mars and Titan are the only planetary bodies or moons where we have landed. One can say that planetary exploration is still in its infancy. Several probes have landed onto the surface of Mars, Venus or the Moon and only one probe has landed onto the surface of the enigmatic moon Titan. That's far from being enough to have a satisfying knowledge regarding another world. The Huygens probe had not landed onto the north polar land of lakes and seas. Thanks to the Cassini orbiter, we know today that Titan reveals different types of environments or landscapes. We need to go back to Saturn's largest moon Titan in order to complete our knowledge of this surprising world. Several worlds in the Solar System clearly require an in-situ exploration. Europa, Titan, Enceladus, Triton and Pluto are complex worlds which may have a dynamic interior.
In spite of our remarkable technological means, we have not been in a position to advance regarding exobiology or intelligent extraterrestrial life. We may be alone and that's a surprising conclusion because we live in a galaxy composed of about 200 billion stars and exoplanets are generally numerous around their main star. Furthermore, there are at least billions of galaxies in the Universe. At this year's American Astronomy Society Division for Planetary Sciences meeting in Provo, Utah, the famous planetologist Alan Stern of the Southwest Research Institute in Boulder, Colorado, proposed an audacious hypothesis to explain the absence of any sign of intelligent lifeform identified. He advanced that if we haven't found any sign of intelligent life or technologically advanced civilization, that's because the intelligent aliens may be evolving beneath the icy crust of their world and may be unable to communicate with other worlds or to study other worlds due to the relatively high thickness of the external crust.
Alan Stern imagines an intelligent lifeform evolving inside a subsurface ocean of liquid water hidden beneath an external icy crust dominated by frozen water. The hypothetical aliens thriving today in the subsurface ocean of liquid water will have to find a way to reach and to colonize the surface. Then, they will be in a position to send artificial signals or to capture extraterrestrial radio signals from other technologically advanced civilizations. Most extraterrestrial intelligent organisms may have to drill too much in order to reach the surface of the icy crust where environmental conditions are likely very different from their usual environment. That kind of configuration may be widespread in the Universe and that may explain the famous conundrum known as the Fermi Paradox which is characterized by the fact that we haven't found any sign of technologically advanced civilizations yet despite the fact that the Universe is composed of an almost infinite number of worlds or planets likely to host a biological system.
The exploration of our Solar System has clearly revealed dynamic worlds rich in frozen water on or in their external crust. The icy moon of Jupiter, Europa, appears to be the perfect example. But one can also mention the volcanically active moon Io where transient pockets of liquid water can take shape and where complex chemical reactions can take shape. The strong electromagnetism generated by the Gas Giant Jupiter is likely to represent a significant obstacle for the development of any lifeform. Around Saturn, multiple moons are dominated by water ice. That's the case for Mimas, Tethys, Dione or Rhea. The Opaque Moon Titan and the tiny moon Enceladus appear to be the most intriguing moons of Saturn today in terms of exobiology. Titan engenders a complex haze made of organics or hydrocarbons, harbors seas, lakes or rivers of liquid methane or liquid ethane and may contain a subsurface ocean dominated by liquid water beneath the presumed icy crust. Enceladus reveals a young south polar region where geysers develop or take shape within the fractures of its icy crust. There may be pockets of liquid water or a global subsurface ocean of liquid water beneath the icy crust of the bright moon.
There are also geysers or cryovolcanoes on the famous moon of Neptune Triton and there may also be cryovolcanoes on the Dwarf Planet Pluto. Images acquired from the New Horizons spacecraft during its historic flyby of the Pluto/Charon System revealed a multitude of relatively big mountains on Pluto. Mountains on Pluto may be dominated by water ice which is very strong in the harsh environment of the planetary body. Drainage channels or fractures can take shape on any icy surface dominated by water ice. Some canyons have been found on Titan, on Enceladus or on Pluto. They reveal dynamic worlds which may contain liquid layers beneath their presumed icy crust. The internal ocean will take shape if there is the right combination of pressure and environmental temperature. There are internal sources of energy and probably hydrothermal vents in the beds of the presumed internal oceans. The hydrothermal vents are likely to bring the right nutrients to the local environment where some lifeforms or ecosystems can take shape and develop like at the bottom of our oceans.
Lifeforms present in the hypothetical subsurface oceans of liquid water may develop and thrive in a particularly stable environment thanks to the strong protection exerted by a relatively deep icy shell against harmful solar radiations and meteorites or comets. A large diversity of species and a complex food chain could more easily develop than on Earth. Here, on Earth, we benefit from a relatively strong magnetic field which prevents high-energy rays such as X-rays or Gamma-rays from reaching the surface. Inside Titan or Europa, any intelligent lifeform thriving in the presumed subsurface ocean of liquid water may be strongly protected by the external crust which would act as a shield against high-energy radiations. Living organisms in the internal oceans of extraterrestrial worlds would probably be bioluminescent like in the abyss of our oceans. What would be the level of intelligence of the most intelligent species in this internal ocean ? Would the most intelligent creatures of this subsurface ocean be able to penetrate or to colonize the surface ?
Humans have not drilled relatively deep at the scale of our globe. Perforating the thick icy shell, from the internal ocean up to the surface, would probably be a huge challenge for the hypothetical intelligent species. The intelligent organisms may not know the night sky or astronomy very well unless they have managed to colonize the surface which may not be suited for them due to low environmental temperatures and relatively low pressures compared to the high pressures they face in their usual environment. They would probably have to wear strongly pressurized gears. Alan Stern imagines that the « space program » of intelligent aliens would be quite boring through to the frozen surface of their world. But once on the surface, the intelligent creatures would probably have the idea to try to communicate with other worlds in space if they have the technology, in particular the technology related to the use of electromagnetic radiations. Alan Stern doesn't provide any significant clues regarding the potential existence of intelligent aliens but he clearly shows the parallel between the prevalence of ocean worlds and the Fermi Paradox. The answer to « Where are they ? » may be found beneath the icy crust of planets or moons like Pluto, Titan or Europa.
Douglas Vakoch who is president of the San Francisco, California-based Messaging Extraterrestrial Intelligence pointed out : « The idea is intriguing » but he added that the Fermi Paradox is more related to the limitation of our technology today. We'll probably have to develop more powerful telescopes or new technologies in order to identify biochemical signatures of life or even intelligent lifeforms elsewhere in the Universe. Alan Stern advanced that if they don't find us first, it could be because they decide long-distance communication isn't worthwhile, especially if they think everybody else is trapped in their own little icy bubbles. Life is really a phenomenon that we don't manage to understand. How did it start ? How did it evolve ? Where do we go ? Are we alone ? Where do we come from ? The myriad of exotic species found in Amazonia or in the abyss, for instance, shows that life often overtakes our imagination. Interior Water Ocean Worlds (WOWs) which may exist in our Solar System may teach us a lot regarding exobiology.
The image above represents a mosaic of views of several moons or planetary bodies of our Solar System which may contain an internal ocean of liquid water. The relative size of each body is respected. One can notice, from the upper part to the lower part of the image, Jupiter's moon Europa, the bright, tiny moon of Saturn Enceladus, Saturn's largest moon Titan, Neptune's moon Triton and the Dwarf Planet Pluto. Europa seems to unveil a type of pack ice that is heavily fractured. Enceladus reveals geysers emanating from fractures in its south polar region. Titan is composed of a deep, thick and opaque atmosphere and unveils bright terrains or mountains contrasting with darker areas dominated by Seif dunes. Saturn's largest moon reveals a methane cycle which may be relatively stable over time and may have a balanced energy budget. Triton unveils a multitude of geysers on its icy surface. Pluto reveals a bright sea of ice and may contain active cryovolcanoes. Those worlds may contain an internal ocean of liquid water where intelligent lifeforms might exist. Montage Credit: Marc Lafferre, 2017.
- To get further information on that news, go to: http://www.sciencemag.org/news/2017/10/why-haven-t-we-had-alien-contact-blame-icy-ocean-worlds and https://guidebook.com/guide/113876/event/16703905.
October 20, 2017 : Some Researchers Identify A Noxious Ice Cloud Above Tropospheric Methane Clouds In Titan's South Polar Region
A group of planetologists working on the basis of data obtained from the Cassini spacecraft during its long mission inside the system of Saturn and its numerous moons reveals evidence of the presence of a noxious ice cloud above the tropospheric methane clouds found above the south polar region of Saturn's largest moon Titan. The noxious ice cloud appears to be thin or wispy and to be composed of at least two molecules, hydrogen cyanide and benzene which represent organics. The outcome confirms the large variety of organics, from simple organics to more complex organics, taking shape or developing in Titan's atmosphere, in the Stratosphere of Titan and in particular in the upper atmosphere of the giant moon where UV light plays a key role in the dynamics of the chemical soup. A large variety of organics or hydrocarbons may become sufficiently heavy to fall onto the surface and to accumulate there in the form of tholins.
The thin and exotic cloud can't be seen with the human eye. The noxious cloud was in fact identified at infrared wavelengths with the Composite Infrared Spectrometer or CIRS from the Cassini orbiter. The cloud appears to be found at an altitude of approximately 100 to 130 miles or 160 to 210 kilometers. As a result, the cloud evolves well above the methane rain clouds developing in Titan's Troposphere which is the lowest area of the atmosphere like on Earth. The wispy cloud of organics covers a significant area near the south pole of the Opaque Moon, from approximately 75 to 85 degrees south latitude. The team of researchers analyzed the spectral signature of the cloud obtained with the CIRS instrument. The spectrum of any atmospheric feature reveals its composition since it represents its chemical fingerprint. The planetologists performed laboratory experiments involving several key molecules or organics in order to obtain a similar spectrum to the spectrum of the enigmatic cloud. They managed to conclude that the ice cloud is composed of a combination of the simple organic molecule hydrogen cyanide together with the large ring-shaped hydrocarbon benzene. Both molecules may have condensed at the same time to form the noxious ice molecules. There is not any separation process between both molecules engendering two different layers with one layer above the other layer.
Carrie Anderson of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is a CIRS co-investigator pointed out : « This cloud represents a new chemical formula of ice in Titan's atmosphere.» She added : « What's interesting is that this noxious ice is made of two molecules that condensed together out of a rich mixture of gases at the south pole.» Data taken from the CIRS instrument had already allowed researchers to identify ice of hydrogen cyanide or HCN in clouds over Titan's south polar region, as well as other toxic compounds in the Stratosphere of the Hazy Moon. Apparently, there is a global circulation pattern of particular gases in the Stratosphere of the Opaque Moon implying a migration of warm gases from the hemisphere experiencing the Summer season to the Winter pole. Clouds tend to accumulate or to build up in the Winter pole and the circulation pattern reverses direction when the seasons change in the southern or northern hemisphere. The northern hemisphere is now experiencing the Summer season whereas the southern hemisphere is experiencing, in parallel, the Winter season. That configuration implies movements of particular gases from the north polar region where it is Summer to the south polar region where it is Winter. Noxious clouds accumulate at a high altitude over the south polar region.
At the beginning of the Cassini mission inside the Saturnian System, we had found evidence of that process of noxious cloud accumulation over the north polar region which was experiencing the Winter season. And near the end of the Cassini mission, recently, a similar phenomenon had been identified over the south polar region. Our understanding upon cloud systems on Titan has changed thanks to the Cassini mission. We had imagined a process involving different types of gas condensing into ice clouds at different altitudes, like a layer of oil above a layer of water. The process of cloud condensation and the location of cloud condensation will intimately depend on the amount or concentration of vapor present and on the temperatures, which get colder and colder as one goes down in the Stratosphere of Titan. However, observations reveal that reality is more complicated than expected because each type of cloud develops over a range of altitudes so that some ices can condense simultaneously, or co-condense.
Carrie Anderson and her collaborators resort to the CIRS instrument in order to sort through the significant amount of complex data obtained in the infrared spectrum regarding the molecules or compounds found in the opaque atmosphere of the giant moon. The device separates infrared radiation into its component colors, like raindrops generating a rainbow observed in the visible spectrum, and measures the strengths of the light at various wavelengths of the infrared spectrum. F. Michael Flasar who is the CIRS principal investigator at Goddard explained : « CIRS acts as a remote-sensing thermometer and as a chemical probe, picking out the heat radiation emitted by individual gases in an atmosphere.» He added : « And the instrument does it all remotely, while passing by a planet or moon.» The new wispy and noxious cloud evolving at a high altitude over the south polar region has a distinctive and very strong chemical fingerprint that was revealed in three sets of observations of the Hazy Moon acquired from July to November 2015. Therefore, the data were obtained during the Autumn season in the southern hemisphere. Each season on Titan lasts approximately seven Terrestrial years. The Winter season in the southern hemisphere started quite recently, in May 2017.
The planetologists had realized that the spectral signatures obtained, regarding the ices of the high-altitude south polar cloud, did not match those of any individual molecule. As a result, they started laboratory experiments in order to simultaneously condense mixtures of gases or compounds. They tried to simulate the environment of Titan's Stratosphere on the basis of an ice chamber in which they tested pairs of molecules or compounds that had infrared spectra in the right portion of the spectrum. At the beginning of the analytical process, the researchers let one gas condense before the other gas. They realized that the best outcome was obtained by injecting both hydrogen cyanide and benzene into the chamber and by allowing both molecules to condense at the same time. If one isolates a benzene molecule, the compound doesn't have a distinctive far-infrared signature. But the team of planetologists allowed benzene and hydrogen cyanide to co-condense and found that the far-infrared signal of the co-condensed ice resembled the far-infrared fingerprint obtained with the CIRS instrument. In other words, the noxious ice cloud may be composed of benzene and hydrogen cyanide.
Researchers will have to perform further analyses in order to determine the structure of the co-condensed ice molecules. Planetologists believe that the ices of the high-altitude cloud are lumpy and disorderly, rather than well-defined crystals. Carrie Anderson and her team had already identified co-condensed ice on the basis of data acquired from the CIRS instrument in 2005. The phenomenon had been noticed near the north pole of the giant moon during the Winter period, approximately two years after the Winter Solstice in the northern hemisphere of the Opaque Moon. The ice cloud had taken shape at a much lower altitude, below 93 miles or 150 kilometers, and its chemical composition was different from the high-altitude ice cloud identified above the south polar region since it contained hydrogen cyanide and cyanoacetylene, one of the more complex organic compounds identified or detected in the Titanian atmosphere.
Carrie Anderson thinks that the differences between the ice cloud found over the north polar region at the beginning of the mission and the high-altitude ice cloud found over the south polar region are related to seasonal variations in the north polar region and in the south polar region. In fact, the observations have not been carried out at the same time of the season since the northern cloud was identified approximately two years after the northern Winter Solstice whereas the southern cloud was identified about two years before the southern Winter Solstice. Environmental temperatures may have been different for instance. One can advance the hypothesis that the composition of gases was slightly different in the two configurations or the hypothesis that environmental temperatures had increased a bit by the time the north polar cloud was found, or both. Carrie Anderson argued : « One of the advantages of Cassini was that we were able to flyby Titan again and again over the course of the thirteen-year mission to see changes over time.» She concluded : « This is a big part of the value of a long-term mission.» Unfortunately, the Cassini spacecraft ended its mission on September 15, 2017 with a crash into the Gas Giant Saturn. Therefore, we will not be in a position to follow and to study the evolution of the high-altitude ice cloud during the long Winter season in the southern hemisphere, on the basis of the remarkable instruments of the Cassini probe.
The image above reveals the night side of Titan, a bright crescent, the orange haze as well as the blue upper layer of Titan's deep and opaque atmosphere. The image represents a natural-color view generated by combining images acquired using red, green and blue spectral filters. The photo was obtained on May 29, 2017 with the ISS Narrow-Angle Camera of the Cassini spacecraft. Methane clouds can develop in the Troposphere of the giant moon. A high-altitude cloud composed of noxious icy compounds above the methane clouds can also develop over each polar area during the Winter season. Image Credit: NASA/JPL-Caltech/Space Science Institute.
- To get further information on that news, go to: https://saturn.jpl.nasa.gov/news/3128/nasa-team-finds-noxious-ice-cloud-on-saturns-moon-titan.
October 13, 2017 : A New Study Reveals That Titan Experiences Intense Methane Rainstorms, In Particular At Mid-Latitudes
A new study reveals that Saturn's largest moon Titan experiences rare and intense methane rainstorms engendering extensive fluvial features or alluvial fans. The most extreme storms may take shape in the mid-latitudes of the Opaque Moon. The research work led by Sean Faulk, a UCLA graduate student, and entitled « Regional patterns of extreme precipitation on Titan consistent with observed alluvial fan distribution » was published on October 9, 2017 in the journal Nature Geoscience. The study also involved the senior author Jonathan Mitchell who is a UCLA associate professor of planetary science, the co-senior author Seulgi Moon who is a UCLA assistant professor of geomorphology and Juan Lora who is a UCLA postdoctoral scholar. The planetologists or geologists were in a position to determine that storms on the Hazy Moon take shape much more frequently than previously believed. They are relatively rare, however, since they develop less than once per Titan year. A year on the Orange Moon is particularly long since it represents 29 and a half Earth years.
Images obtained from the Huygens probe during the atmospheric descent on January 14, 2005 had revealed a dark plain and bright hills composed of dark drainage channels. We realized that there is rainfall there from time to time. But how frequent does methane rain occur in the area of Shangri-La and Adiri ? The new paper makes things clearer. Jonathan Mitchell pointed out : « I would have thought these would be once-a-millennium events, if even that. » He added : « So this is quite a surprise.» On Titan, the environmental temperature is extremely low, water appears in its solid form and the clouds that we can encounter are generally composed of hydrocarbons like methane or ethane. Dynamic cloud systems or storms have been found in the polar areas as well as at mid-latitudes or low latitudes. Clouds remain rare at low latitudes on Titan. After the Equinox of 2009, we had observed large cloud systems at low latitudes or mid-latitudes. Monsoon events engendering massive floods may have taken shape at low latitudes in the dark areas during that period.
The Seif dunes found in the dark areas of the low latitudes of the giant moon demonstrate the action of erosional processes, winds or rainfall of methane. A parallel can be drawn between the dunes of Titan and the dunes on Earth. Titan looks like the Earth to a certain extent. There are lakes, seas and rivers or drainage channels at high latitudes, in particular in the northern hemisphere. Jonathan Mitchell who is the principal investigator of UCLA's Titan climate modeling research group advanced : « The most intense methane storms in our climate model dump at least a foot of rain a day, which comes close to what we saw in Houston from Hurricane Harvey this summer.» Sean Faulk also determined that the extreme methane rainstorms may sculpt the icy surface of the hazy world in much the same way that extreme rainstorms sculpt the rocky surface of our planet.
The team of researchers managed to find a correlation between the appearance of the areas where heavy storms or strong methane rainfalls occur and the potential intensity of precipitations. The planetologists recently identified alluvial fans which are likely related to the periodic and heavy rainfalls of methane which are believed to take shape in the area. Heavy rainfall on Earth can produce rivers and engender large flows of sediment that invade low lands and form cone-shaped features or alluvial fans. Titan undergoes the same kind of process as the Earth with liquid methane or liquid ethane. Seulgi Moon argued that the outcome of the study clearly shows the role of extreme precipitation in sculpting the surface of the Orange Moon. She added that the pattern of alluvial fan development likely applies to Mars and to other planetary bodies. On Mars, one can observe large alluvial fans even if the planet is devoid of any liquid water present on the surface today. Planetologists need to precisely understand the interaction between rainfall of methane and the ground in the prospect of better analyzing the impact of climate change on Earth and other worlds.
During the long mission of the Cassini spacecraft which started in mid-2004 and ended in September 2017 with a crash into the Gas Giant Saturn to avoid contaminating other worlds like Enceladus or Titan, we have obtained remarkable views of Titan's surface thanks to infrared or near-infrared data and radar data in particular. The alluvial fans of Saturn's largest moon have been identified via the radar instrument of the orbiter. Juan Lora argued that the Cassini probe has produced a revolution in the understanding of researchers regarding the Opaque Moon. Infrared or near-infrared data have revealed for the first time a stable extraterrestrial lake or sea in the south polar region of Titan. Radar data have revealed that the dark areas or the low-albedo areas found at low latitudes are dominated by Seif dunes or parallel and linear dunes extending over long distances. The high latitudes of the northern hemisphere appear to be the most humid areas on Titan today. Planetologists want to know why.
The team of Sean Faulk managed to determine that the alluvial fans on the Orange Moon are mostly found between 50 and 80 degrees latitude. In fact, they tend to appear close to the centers of the northern and southern hemispheres but they are generally a little bit closer to the poles than to the equator. Titan is far from being a uniform world since there is a strong contrast between bright areas and dark or low-albedo areas. Clouds at low latitudes on Titan are rare but they can develop rapidly and produce heavy rainfalls engendering floods, rivers or runoffs. The landscape takes shape under the influence of prevailing winds or methane rain like on Earth. The air at the level of Titan's surface is denser than the air at sea level on Earth. As a result, the significant atmosphere of Titan engenders significant erosional processes. Canyons, fractures, sinuous channels or irregular terrains can be found on the Opaque Moon. The dunes can take shape in dry areas like in the dark regions located at low latitudes.
Previous models have revealed that liquid methane tends to be mostly found on the surface at higher latitudes of the exotic world. The new analysis is the first work to bring key information regarding the behavior of extreme storms of liquid methane that are likely to engender a major sediment transport and strong erosional processes. The relationship or the interaction between the soil and rainfall is clearly unveiled. The long mission performed by the Cassini spacecraft allowed researchers to study Titan's climate and meteorology during three Titanian seasons. The analysis of Titan's hydrology turned out to be particularly complicated. We'll have to go back to Titan in order to collect new data regarding Titan's atmosphere and surface and to completely fill the puzzle. Seasons appear to play a key role on Saturn's largest moon. Today, researchers primarily resort to computer simulations to analyze Titan's hydrologic cycle due to the difficulty to collect reliable data upon precipitations on Titan. The planetologists determined that the most intense rainstorms take shape near 60 degrees latitude. That's the latitude which corresponds to the area where alluvial fans are most heavily concentrated. The specialists noted however that rain mostly occurs in the polar regions where lakes, seas and rivers are mostly found during a typical Titanian year.
Researchers have advanced that there may be long term transports of liquid methane between the south polar region and the north polar region because the north polar region is today much wetter than the south polar region where only one major pool of liquids has been identified. Ontario Lacus whose shape is reminiscent of a foot or kidney may be a pond and its level and size may significantly vary over the course of a Titanian year. Kraken Mare, located in the high latitudes of the northern hemisphere, is by far the largest body of surface liquids on Titan. Ligeia Mare and Punga Mare are two other major lakes or seas which have been well discerned in radar images acquired from the Radar Mapper of the Cassini orbiter. Multiple islands, bays, peninsulas or drainage channels can be identified in the area of Ligeia Mare. Planetologists are wondering whether there are internal sources of methane fuelling the lakes or seas in the north polar region.
Researchers are astonished by the relatively high concentration of methane present in Titan's atmosphere today. Methane tends to be destroyed by ultraviolet light from the Sun in the long term. That's why the hypothesis involving internal sources of methane appears strong. There may be a methane cycle between the underground, the ground and the atmosphere where evaporation processes, condensation processes and precipitation processes can take shape. The study led by Sean Faulk and funded by a NASA Cassini Data Analysis and Participating Scientists Program grant reveals that intense storms can form due to the sharp contrast between the wetter, cooler weather encountered in the higher latitudes and the drier, warmer weather encountered in the lower latitudes. That's a process which has been well studied on Earth where cyclones or hurricanes form and develop in the mid-latitudes due to temperature contrasts. Storms or blizzards which are regularly encountered during the Winter months across much of North America follow the same meteorological rule.
The image above reveals a giant arrow-shaped cloud and surface features on the Opaque Moon Titan at the beginning of the Spring season in the northern hemisphere and of the Autumn season in the southern hemisphere. The previous equinox had occurred in August 2009. The view represents a mosaic of Titan based on near-infrared data centered at 938 nanometers acquired from the Narrow-Angle Camera of the Cassini spacecraft on September 27, 2010 and on July 9, 2010. Most of the view was generated on the basis of the view taken on September 27, 2010. The bright cloud, probably related to seasonal factors, may have produced heavy rainfalls. Image Credit: NASA/JPL/Space Science Institute.
- To get further information on that news, go to : http://newsroom.ucla.edu/releases/intense-storms-batter-saturns-largest-moon-ucla-scientists-report and https://www.nature.com/articles/ngeo3043?foxtrotcallback=true.
September 16, 2017 : The Cassini/Huygens Spacecraft Revealed That Titan Is A Dynamic World With An Exotic And Original Meteorology
Data obtained from the Pioneer 11 spacecraft, the Voyager 1 spacecraft and the Voyager 2 spacecraft had allowed us to notice that Saturn's largest moon Titan was a captivating and intriguing world. Researchers and the general public realized that Titan had a thick, dense, deep and completely opaque atmosphere like no other moon in the Solar System. Unfortunately, they were frustrated to a certain extent because they had not been in a position to observe any surface features of the giant moon. They knew that Titan's atmosphere was dominated by molecular nitrogen like our own atmosphere. They also knew that there was a relatively significant concentration of methane in Titan's atmosphere and that the environmental temperature of the Orange Moon was particularly low despite the potential greenhouse effects engendered by the hazy atmosphere. Planetologists became aware that the Opaque Moon might contain oceans, seas or rivers of methane or hydrocarbons.
A revolution in our understanding and knowledge of Titan occurred with the Cassini-Huygens mission which started in mid-2004 with the Saturn Orbit Insertion of the Cassini-Huygens spacecraft into the Saturnian System. We know now that Titan is an active world generating complex chemical processes and undergoing significant erosional processes. The set of instruments on board the Cassini spacecraft and on board the Huygens probe has allowed us to see through the hazy atmosphere of Titan and to discern remarkable surface features. Infrared or near-infrared data obtained from the Cassini probe revealed a significant contrast between dark and bright surface features on the Orange Moon. Dark features are mostly found at relatively low latitudes. Bright features can represent mountains, hills, ice chunks or plateaus. Prior to the plunge of the Huygens probe into Titan's atmosphere and the historical touchdown, some planetologists had advanced that the dark regions found at low latitudes could represent seas or oceans of liquid methane or liquid ethane.
The Huygens probe landed onto the surface of Saturn's largest moon at a low latitude in the region of Adiri and Shangri-La on January 14, 2005. During the atmospheric descent of Titan, the probe acquired a multitude of panoramic views of Titan's surface revealing a sharp contrast between bright hills or mountains and a dark plain. The aerial views made some viewers think that the dark plain could represent a sea of methane. However, the views of Titan's surface obtained from the Huygens probe after its landing onto the dark area showed that the probe had not landed onto a sea or lake. The basic color view unveils a brown or orange landscape with eroded stones or pebbles implying that the probe may have landed onto an ancient river, stream or brook. The aerial images had clearly shown dark fractures or drainage channels within the bright hills as well. All those elements or landscape features make researchers advance that there may be regular rainfalls or monsoon events in the area.
Thanks to radar data obtained from the Radar Mapper of the Cassini spacecraft, planetologists rapidly noticed that the dark areas found at low latitudes were dominated by Seif Dunes or linear and parallel dunes extending over long distances. We could compare those dune fields to cat scratches. The radar views of Seif Dunes on Titan bring significant clues regarding the strength or the orientation of prevailing winds. The dark dunes may contain organics or hydrocarbons like benzene. Are the dunes observed in the dark areas of the low latitudes related to the presence of ancient seas or oceans ? On Earth, for instance, the Sahara Desert lies on an ancient sea. Some dunes have been seen or identified on Mars as well. Complex photochemical processes in Titan's atmosphere may engender large molecules or compounds falling to the surface and forming a red or dark material known as Tholin. The radar-dark regions of Fensal, Aztlan or Shangri-La appear to be dominated by Seif Dunes. Those regions mark a radical contrast with bright regions like Adiri or Xanadu which may be dominated by water ice, mountains, hills or an irregular terrain.
The first extraterrestrial body of stable surface liquids was identified in 2005 in the high latitudes of the southern hemisphere of Titan via infrared or near-infrared data obtained from the Cassini orbiter. The lake which looks like a foot or a kidney is known as Ontario Lacus. Ontario Lacus may be mainly composed of methane, ethane and propane. The lake was first identified during the Summer season in the southern hemisphere of the Opaque Moon. Several dynamic clouds have been observed in the area of this intriguing lake during the Summer season implying the presence of evaporation processes, condensation processes and precipitation processes. In fact, the methane cycle on Titan can be compared to the water cycle on Earth even if environmental temperatures on both worlds are significantly different. Researchers were surprised to notice that the areas of the low latitudes of Titan appear dry whereas the high-latitude areas appear relatively humid. Are the liquid hydrocarbons found on the surface of Titan particularly sensitive to the strength of solar radiations ?
Planetologists have noticed that most cloud systems develop at high latitudes on Titan. In the low latitudes or in the middle latitudes, transient elongated clouds or cirrus clouds have been observed during the Cassini-Huygens mission. Scientists became aware that seasonal factors may play a key role in the dynamics of Titan's atmosphere and meteorology. As soon as 2006, radar views taken from the Cassini orbiter revealed the wetlands of Titan's northern hemisphere during the Winter season. The high latitudes of Titan's northern hemisphere or the north polar region of the Orange Moon appear to be the most humid areas on Titan. Several lakes or seas such as Kraken Mare, Ligeia Mare and Punga Mare were identified in the high latitudes of the northern hemisphere thanks to the Radar Mapper of the Cassini orbiter. Radar views clearly reveal familiar features such as drainage channels, islands, bays or peninsulas. Infrared or near-infrared data acquired from the Cassini spacecraft also unveiled a huge ethane cyclone or vortex engulfing the north polar region in 2006 during the Winter season in the area.
The Equinox marking the end of the Winter season and the start of the Spring season in the northern hemisphere occurred in 2009. Planetologists monitored the evolution of the meteorology in the polar areas as well as at low latitudes in order to try to better understand the dynamics of the methane cycle on Titan. They noticed an outburst of cloud activity at low or middle latitudes in 2010 with large elongated clouds which developed and dissipated relatively rapidly. During that meteorological phenomenon, heavy rainfalls may have occurred in the area as the infrared or near-infrared views show. During the Autumn season in the southern hemisphere, a yellow vortex composed of complex organics, evolving above the south polar region of the Opaque Moon, was observed from the Cassini probe in 2012. Complex photochemical reactions in the upper atmosphere of Titan take shape and engender new elements or molecules such as methane, ethane, propane, acetylene or radicals.
Researchers are surprised to identify a relatively significant concentration of methane in Titan's atmosphere because in the long run, methane molecules tend to disappear under the action of ultraviolet light from our star in particular. Are there internal sources of methane replenishing the exotic atmosphere of Saturn's largest moon ? Are the north polar lakes or seas of Titan exclusively related to the methane cycle ? Is there an underground network of liquid methane with pockets or seas of methane ? Is there a layer of liquid methane beneath the icy crust of Titan ? Tidal forces related to the gravity of Saturn and the other moons of the Gas Giant may play a key role in the dynamics of the interior of Titan. Some researchers have advanced that there may be a subsurface ocean of liquid water as well. During the Cassini mission, scientists have had the opportunity to observe solar radiation glinting off of the lakes located in the high latitudes of the northern hemisphere as the Sun went up over those surface bodies of liquid hydrocarbons.
Researchers are far from clearly understanding the dynamics of Titanian lakes. The famous « Magic Island » still remains a mystery. Planetologists had noticed, on the basis of several radar views, the appearance of a bright feature close to the coast within the north polar lake or sea Ligeia Mare. Was it a new island ? Later, the new radar images revealed that the shape of the bright features had changed and dissipated. Recent views demonstrate that the Magic Island has completely disappeared. Therefore, was it really a transient island ? Was it a cryovolcano ? Was it an iceberg ? Was it a field of bubbles ? Was it an area of strong waves ? Was it an area of strong fog ? Nobody really knows and we can only advance hypotheses. Titan demonstrates that nature can be more exotic than we could imagine. Titan may have new mysteries and more surprises to reveal. Planetologists and biologists want to know more about the chemistry of organics on Titan which may be more complex than expected.
The atmosphere of the Opaque Moon may resemble the atmosphere of the Early Earth before life emerged. The Titanian atmosphere draws the attention of biologists because it contains a relatively large amount of hydrocarbons or organics. The Orange Moon may represent a natural prebiotic laboratory. In the harsh environment of Titan, complex organics can develop. Some researchers have advanced the hypothesis of the potential presence of an exotic lifeform based on methane on Titan. Thomas Zurbuchen who is associate administrator for NASA's Science Mission Directorate at Headquarters in Washington pointed out : « Cassini has transformed our thinking in so many ways, but especially with regard to surprising places in the solar system where life could potentially gain a foothold.» He added : « Congratulations to the entire Cassini team !». The lakes or seas of Titan may be the right places to look for life. We have gathered data or clues regarding the nature, the dynamics or the depth of the lakes or seas found in the high latitudes of Titan but we can't say if they shelter an exotic lifeform today. An In-Situ mission with a boat, a drone or a submarine would be ideal to study the environment or to perform oceanography.
The seas or lakes of Titan may have been bigger in the past. The methane cycle of Titan at the present time may bring us clues regarding the water cycle of our own planet in the far future. If the amount of solar radiation received by the Earth significantly increases, the oceans at lower latitudes may tend to progressively vaporize and lakes, seas or oceans may start to develop in our polar regions. Titan may be a great place for explorers or hikers with its diversity of environments or landscapes from canyons to rivers, lakes, seas, mountains or potential cryovolcanoes spewing water ice or water lava. Specialists from planetologists to biologists are wondering whether there is an hydrothermal biochemistry in the presumed subsurface ocean of salty liquid water of Titan. The Cassini team had planned a crash against the Gas Giant Saturn for the Cassini spacecraft, on September 15, 2017, in order to avoid any potential contamination of moons like Enceladus or Titan because there may still be bacteria, archaea or fungi on the Cassini orbiter today.
The image above reveals the region of the dark feature Ontario Lacus. Ontario Lacus whose shape is reminiscent of a foot or kidney was the first surface body of liquids identified on Titan. Some bright features found in the lower part of the image may represent clouds of hydrocarbons such as methane or ethane. The view corresponds to a mosaic or composite of three images captured over several minutes during the distant flyby of the Opaque Moon performed by the Cassini spacecraft on June 6, 2005. The views were acquired by the Narrow-Angle Camera of the Cassini orbiter on the basis of a combination of spectral filters sensitive to wavelengths of polarized infrared radiation. The area of Ontario Lacus was experiencing the Summer season during the historical flyby of 2005. Image Credit: NASA/JPL/Space Science Institute.
The natural color image above unveils a high-altitude vortex over the south polar region of Saturn's largest moon Titan. The view was obtained on June 26, 2012 from the Narrow-Angle Camera of the Cassini spacecraft before a distant flyby of the Opaque Moon planned on June 27, 2012. The yellow vortex or cyclone is developing during the Autumn season in the southern hemisphere of the giant moon. The Autumn season in the southern hemisphere had started in August 2009 with the Equinox. The hazy atmosphere of Titan is remarkably deep with multiple layers. Methane or ethane clouds can take shape in this atmosphere dominated by nitrogen. Image Credit: NASA/JPL-Caltech/Space Science Institute.
- To get further information on that news, go to: https://saturn.jpl.nasa.gov/news/3111/after-cassini-pondering-the-saturn-missions-legacy, https://saturn.jpl.nasa.gov/news/3087/nine-ways-cassini-matters-no-4, https://saturn.jpl.nasa.gov/news/3086/nine-ways-cassini-matters-no-3, https://saturn.jpl.nasa.gov/news/3085/nine-ways-cassini-matters-no-2 or https://saturn.jpl.nasa.gov/news/3084/nine-ways-cassini-matters-no-1.
September 11, 2017 : The Cassini-Huygens Mission Brought Key Discoveries Regarding The Intriguing Moon Titan
The Cassini-Huygens mission inside the Saturn System which started in mid-2004 has allowed us to gather significant clues or to perform key discoveries regarding the structure of Titan, the nature of its surface, the dynamics of its atmosphere, the meteorology and the seasonal phenomena on Titan or the nature of the soil on the giant moon. The Cassini spacecraft and the Huygens probe have unveiled a surprising world where familiar processes can take shape. Today, we know that there are lakes, seas, rivers, canyons, tectonic processes, cyclones, clouds, fields of dunes or mountains on Saturn's largest moon thanks to the Cassini orbiter and the Huygens probe. We have answered some questions but we have found new questions or puzzles.
A major milestone took shape on January 14, 2005 when the Huygens probe from ESA carried out an atmospheric descent to the surface of Titan. The probe contained six instruments, four instruments led by European principal investigators and two instruments led by specialists from the United-States. From the separation between the Cassini spacecraft and the Huygens probe, the Huygens lander performed an approach of Titan lasting twenty days and on January 14, 2005, it carried out the famous atmospheric plunge during which it gathered key data regarding Titan's atmosphere or environment. The atmospheric approach lasted two and a half hours until the touchdown. We obtained a large amount of data regarding the atmospheric pressure, the temperature or the density of the hazy atmosphere of the Orange Moon.
The atmosphere of Titan, which is dominated by nitrogen like our atmosphere and which contains a relatively significant concentration of methane, unveils super-rotating winds. The Huygens probe also collected data regarding the chemical composition of Titan's haze. The panoramic views acquired during the atmospheric plunge revealed a dark plain and bright hills containing dark fractures or drainage channels. Those geographical features suggest that it probably rains from time to time in the area. The rain can't be made of water since the environmental temperature evolves around minus 179 degrees Celsius, minus 290 degrees Fahrenheit or 94 Kelvin. The rain on Titan is probably dominated by methane which can appear in its liquid form in the exotic environment of the Orange Moon. The images captured from the Huygens probe after the historic touchdown unveiled eroded stones or pebbles leading planetologists to advance that the Huygens probe had probably landed onto an ancient brook, stream or river. From the ground, the Huygens lander sent data to the Cassini orbiter for another 72 minutes until the Cassini spacecraft vanished over the horizon.
The Cassini orbiter will have performed 127 targeted close flybys of Titan acquiring infrared, near-infrared or radar images of Titan's surface. The Visual and Infrared Mapping Spectrometer (VIMS), the Radar Mapper or the Radio Science System which incorporates the high-gain antenna of ASI have allowed us to determine that most lakes or seas on Titan are located in the high latitudes of the Opaque Moon and that the surface bodies of liquid represent a surface area higher than 1.6 million square kilometers that is to say a surface area covering almost 2 percent of Titan's surface. The high latitudes of the northern hemisphere appear to be the most humid area today. A research work led by Alice Le Gall at the Laboratoire Atmosphère, Milieux in France unveiled that Ligeia Mare, a major sea or lake in the north polar region, is composed of pure methane. A group led by Marco Mastrogiuseppe at Università La Sapienza, Rome, in Italy, managed to determine, on the basis of radio sounding, that the depth of the sea or lake could reach 160 meters in some portions of the sea or lake. That was the first time we performed oceanography or the measurement of the depth of a stable liquid body on another world.
The specialists also determined, on the basis of the analysis of thermal emission, that the seabed is composed of a layer of organic-rich sludge. There is apparently a methane cycle involving evaporation processes, condensation processes and precipitation processes on Titan. Heavy molecules, complex molecules or insoluble and heavy compounds like nitrile or benzene may sink to the bottom of the sea or lake where they can form the sludge identified by the team of Marco Mastrogiuseppe. In parallel, Thomas Cornet and his collaborators at the Université de Nantes, France, identified ephemeral lakes or big, shallow depressions which can be regularly filled with liquid hydrocarbons depending on seasonal factors like on the Blue Planet. The first extraterrestrial lake or sea identified was Ontario Lacus, a lake or sea found in the high latitudes of the southern hemisphere of Saturn's largest moon. The level or the size of Ontario Lacus may not be stable over time because the lake or sea may be closely related to subsurface hydrocarbon fluids which can go up and flood the depression or go down and trigger a decrease in the level or in the size of the lake or sea. The radar views of the area of Ontario Lacus suggest the presence of sediments around Ontario Lacus. One can deduce that the lake or sea may have been bigger with a higher level in the past.
The Radar Mapper of the Cassini spacecraft has also allowed researchers to identify and to analyze large areas of Seif Dunes or parallel and linear dunes extending over long distances at low latitudes. The dunes which can move under the influence of prevailing winds represent approximately 13% of the surface of Titan or cover more than 10 million square kilometers. The exotic and giant dunes of Titan may be dominated by solid hydrocarbons that fall from the hazy atmosphere. The dunes appear to be between 1 and 2 kilometers wide on average, to extend over hundreds of kilometers and to be about 100 meters high. Alice Le Gall and her collaborators managed to determine that the size and spacing of Titanian dunes vary across the surface and that those characteristics are apparently closely related to the altitude or the latitude. We could determine that the main dune fields are located in lowland regions at the equatorial level and that the dune fields at higher elevations appear narrower and more widely separated, implying a thinner layer of sand. Sand particles may be less mobile in the high latitudes of the northern hemisphere because the area appears particularly humid or wet. The grains of sand can be displaced by low-speed winds in multiple directions during the remarkably long Titanian year engendering dune movements like in the Sahara for instance.
Researchers have gathered major clues regarding the potential presence of a subsurface ocean beneath the icy crust of the Opaque Moon. The Huygens probe had been in a position to detect electrical currents in the upper atmosphere of Titan implying the presence of a subsurface ocean. This configuration of radio signals led us to deduce the presence of an underground ocean at a depth between around 55 km and 80 km beneath the presumed icy crust. The radio science system of the Cassini orbiter allowed the team of Luciano Iess at the Università La Sapienza in Rome to analyze the internal structure of the giant moon on the basis of the way the Cassini probe was pulled off course by the Orange Moon as it flew by. Researchers were in a position to measure gravity variations along the trajectory via deviations in the velocity detected with the radio signals of the orbiter transmitted to radio stations. Planetologists determined the distribution of mass inside Titan and inferred constraints on its internal structure. This subtle technique also allowed scientists to deduce tides on the Opaque Moon that distort the ground by more than 10 meters. All those data imply the presence of a subsurface ocean which is likely composed of liquid water. This presumed ocean with swirling water may be up to 250 kilometers deep and may be hidden under a relatively thick ice shell around 50 kilometers deep.
If there is a subsurface ocean of liquid methane or if there are pockets of liquid methane beneath the icy crust of Titan, one could explain more easily the remarkably high concentration of methane in Titan's atmosphere because, over time, methane tends to be destroyed by ultraviolet light from the Sun. The volume of liquid methane found on the surface appears insufficient to account for the relatively significant concentration of methane in Titan's atmosphere. That's why we suspect the presence of a subsurface reservoir of liquid methane. Researchers are trying to better understand the methane cycle, the meteorology and seasonal phenomena and the mechanics in the production of the organic haze on the Opaque Moon. Some researchers led by the principal investigator Hunter Waite at the US Southwest Research Institute have used Cassini's Plasma Spectrometer or CAPS to analyze the building blocks of the compounds of the organic haze. Andrew Coates and his collaborators at University College London's Mullard Space Science Laboratory in the UK which proposed the instrument's electron spectrometer, identified large negatively charged molecules in the upper atmosphere of the Opaque Moon which is quite surprising. The ultraviolet light from our star and the energetic particles related to Saturn's magnetosphere tend to ionize atoms or molecules found in the upper atmosphere and engender new molecules or elements like nitrogen, methane or acetylene. Scientists had anticipated an abundance of positively charged compounds but not negatively charged compounds because negatively charged compounds are highly reactive and should rapidly combine with other atoms, ions or molecules. The negative ions may play a key role in the development or the formation of the haze. A recent analysis some 10 years after the initial detection from the Cassini orbiter unveiled the discovery of linear carbon chain molecules at an altitude of approximately 1000 kilometers. Those molecules feed the larger organic molecules located at a lower level in the atmosphere.
The atmosphere of Titan appears remarkably complex with its myriad of organics or hydrocarbons. The atmosphere of Titan, today, may resemble the atmosphere of the Early Earth before life emerged. Researchers consider Titan as a prebiotic natural laboratory. The study of the organics on Titan may bring clues to the origin of life on Earth. And some researchers advance that there may be an exotic lifeform on Titan today. The team led by Nick Teanby from the University of Bristol in the UK analyzed the rapid seasonal change of the Opaque Moon following the Equinox of August 2009 on the basis of Cassini's Composite Infrared Spectrometer device and was in a position to observe the formation of a cyclone or swirling vortex and a build up of exotic gases at surprisingly high altitudes of approximately 400 kilometers above the south polar region of Titan. The development process took shape remarkably rapidly in around six months which is far less than a Titanian season. The south-polar vortex showed that seasons play a key role on Titan. Cooler air tends to go down from warmer high altitudes. A group led by Remco de Kok of Leiden Observatory and SRON Netherlands Institute for Space Research resorted to the Visual and Infrared Mapping Spectrometer or VIMS to obtain key data that allowed the team to determine that the giant cyclone is composed of frozen particles of the toxic molecule hydrogen cyanide or HCN unveiling that the temperature of the atmosphere is as low as -148 degrees Celsius, in line with the rapidly cooling atmosphere related to seasonal changes.
Researchers could also analyze the ionosphere which represents the ionized layer or the upper part of Titan's atmosphere. The study could be done on the basis of CAPS and Cassini's Langmuir Probe, which was proposed by the Swedish Institute of Space Physics and which is part of the US-led Cassini Radio and Plasma Wave Science (or RPWS) package. Planetologists could identify the interactions between the ultraviolet light from the Sun, the energetic particles from the magnetosphere of the Gas Giant and the compounds of Titan's upper atmosphere which tend to be ionised. A complex organic chemistry can take shape in that soup of elements or molecules and during that process, a loss of atmospheric compounds is observed in parallel. From the first flybys, the Langmuir probe allowed the specialists to determine the interactions between Saturn's magnetosphere and the dynamics of the ionosphere of Saturn's largest moon. The Gas Giant and its magnetosphere have a common rotation period of almost 11 hours, as deduced from radio data. Titan spends approximately 95% of its time inside the magnetosphere of the Ringed Planet which implies a plasma flow that erodes the upper atmosphere of the Opaque Moon. The loss over billions of years appears remarkably high since we determined that approximately seven tonnes per day of atoms, ions or molecules were leaving the atmosphere, on average dominated by heavy ions.
The team led by Michele Dougherty at Imperial College London found, on the basis of the magnetometer of the Cassini probe, that the Opaque Moon does not have its own intrinsic magnetic field. The magnetometer also allowed researchers to bring information regarding the interaction between Titan and the outer fringes of the magnetosphere of the Gas Giant. Analyses based on the combination of the magnetometer data, the Cassini Plasma Spectrometer and the Radio and Plasma Wave Spectrometer revealed that when the Orange Moon is temporarily outside of the magnetosphere of the Ringed Planet, the atmosphere of Titan keeps a memory of the magnetic field of the plasma that is found around the Gas Giant. When the Opaque Moon was directly exposed to the solar wind, researchers using the magnetometer noticed that the giant moon behaves like other unmagnetised planetary bodies like Venus or Mars, with the solar wind draped around the Titanian atmosphere. Planetologists want to know if Titan's atmosphere is stable over time, if there is a net loss in the atmospheric mass of Titan. The studies related to the magnetosphere of Saturn, the solar winds and the ionization processes in Titan's atmosphere help us to bring key information regarding our understanding of the dynamics of Titan's atmosphere.
The image above represents a portion of a radar swath obtained from the Cassini orbiter during the T17 Flyby performed on September 7, 2006. One can notice linear and parallel dunes extending over long distances and influencing the shape of bright topographic features. Dune fields tend to be found in the dark areas of the low latitudes. The dunes tend to be sculpted by prevailing winds. Image Credit: NASA/JPL/Cassini Radar Team/Jason Perry.
- To get further information on that news, go to: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Celebrating_Europe_s_science_highlights_with_Cassini.
August 12, 2017 : Cassini Data Have Revealed That Several Saturnian Moons Including Titan, Enceladus Or Iapetus Can Potentially Host Life
Since the start of the Cassini mission inside the Saturn System, the Cassini spacecraft and the Huygens probe have gathered a huge amount of data regarding Saturn and its numerous moons. Some moons like Tethys, Dione or Rhea appear bright and are heavily cratered. Some moons like Titan, Iapetus or Enceladus are particular. Titan which is by far the largest moon of Saturn has a massive atmosphere which appears completely opaque from outer space. Iapetus has two different types of terrain, a dark terrain and a bright terrain which marks a sharp contrast with the bright terrain. Enceladus has a young surface in the south polar region where fractures known as the Tiger Stripes can be clearly noticed. Geysers spewing water ice appear in the area of the fractures. Is there an ocean of liquid water or are there pockets of liquid water beneath the surface of Enceladus ?
As soon as the flyby of Enceladus performed by the Voyager 2 spacecraft in 1981, Enceladus captured the attention of researchers and the general public because it appeared remarkably bright and smooth with relatively few craters compared to other Saturn moons like Tethys, Dione or Rhea. The fact that the surface of a region of the moon is smooth implies that the area is geologically active since there is no significant atmosphere. No cryovolcano or geyser had been identified on Enceladus at the time of the flyby. The Cassini probe allowed researchers to clearly identify geysers or plumes of water in the south polar region of Enceladus in 2005, thanks to the cameras of the orbiter. Several flybys carried out by the Cassini spacecraft showed that the region of the Tiger Stripes was approximately 180 degrees Fahrenheit or 100 degrees Celsius warmer than the rest of the surface of the tiny satellite. Scientists managed to determine the close relationship between the fractures or cracks in the icy crust and the heat source. Those plumes of water appear to be propelled at a speed of approximately 800 miles per hour or 1,300 kilometers per hour.
On March 12, 2008, the Cassini spacecraft performed an extremely close flyby of Enceladus above the area of the plumes in the south polar region at an altitude of 31 miles or 50 kilometers so that it could sample the plumes. As a result, we determined that the plumes were composed of water mixed with ammonia, methane and carbon dioxide. By April 2014, we came to the conclusion that the geyser compounds were salty and contained potassium and sodium. Therefore, the geyser compounds found above Enceladus are very similar to the sea spray we encounter on Earth. We also found hydrogen gas and silicate crystals in the sprays. Planetologists reported that silicate crystals could only have taken shape in boiling water. That's why we strongly believe that there is an internal ocean of salty liquid water beneath the icy crust of Enceladus. This exotic ocean may appear above a hot, rocky seafloor where various minerals may be found and where hydrothermal vents may be encountered like in the abyss of our oceans. Are there hydrothermal vents on Enceladus with chimney-like structures like the « Black Smokers » or the « White Smokers » that we can observe in the volcanically-active areas of our oceans on Earth ? The hot spots of Enceladus may be the right place to look for water-based life or may correspond to oases of life from simple organisms like bacteria or archaea to multicellular organisms like fish. We'll have to build probes and instruments suited to identify amino acids, fatty acids or proteins.
Titan is also an intriguing world with its complex atmosphere, its photochemical haze, its lakes, seas and rivers and its presumed subsurface ocean. The environmental temperature on the Opaque Moon is too low to allow the presence of liquid water on its surface. The liquids which can appear in their liquid form on the surface of Titan are methane, ethane and propane. The liquids present on the surface of Saturn's largest moon can contain nitrogen or nitrogen-bearing molecules. Water may be widespread in its solid form on the surface of Titan. Water may be as hard as the rocks we can encounter on Earth. The haze of Titan which is rich in organics or hydrocarbons makes the atmosphere opaque in the visible spectrum. The Cassini probe can discern surface features with the Radar Mapper or with its infrared or near-infrared eyes. The first pool of liquids identified on Titan was Ontario Lacus in the high latitudes of the southern hemisphere. Later, radar data revealed that the high latitudes of the northern hemisphere unveiled a large concentration of lakes, seas and rivers.
The Huygens probe landed at a low latitude of Titan on January 14, 2005. During its atmospheric descent, it revealed familiar landscape features such as hills, plains and fractures or drainage channels as well as a significant contrast between a bright area made of hills and a dark, orange or brown plain which may correspond to an ancient sea. The dark drainage channels imply rainfall. Like on Earth, there is a meteorological cycle on Titan but the Titanian meteorological cycle involves methane which can evaporate, condense, form clouds and fall as rain. The images obtained from the ground unveiled the presence of pebbles or eroded stones on the landing site. The pebbles may be mainly composed of water. The Huygens probe may have landed onto an ancient river or brook. The aerial views acquired from the Huygens probe unveiled a familiar panorama with what seemed to be a coastline and dark drainage channels. Currently, the dark areas of the low latitudes of Titan are dominated by Seif Dunes as the radar images acquired from the Cassini orbiter show.
Researchers believe that the interior of Titan is warm due to tidal forces exerted by Saturn and the other Saturn moons. They have strong clues that there is a subsurface ocean of liquid water beneath the presumed icy crust. During its revolution around Saturn lasting 16 Terrestrial days, the shape of the Opaque Moon is distorted or changes. Thanks to Cassini data, planetologists were in a position to measure the tidal bulging of the Orange Moon and to determine that the surface rises or falls on the order of 30 feet or 9 meters. If Saturn's largest moon were completely solid, the tides on Titan would be at least 10 times lower than what is observed or deduced as researchers advance. The data regarding tidal bulging or the Radio-science analyses based on Cassini signals transmitted to NASA's Deep Space Network imply that Titan contains an internal ocean beneath the icy crust. The icy crust is likely mainly composed of water in its solid form. Beneath the internal ocean, there may be another icy crust with a higher density and undergoing a high pressure. The core of Titan may be composed of a mixture of silicate and water. Scientists believe that the floor of the internal ocean is cold, frozen or compacted preventing the release of key minerals for the development of any potential lifeform. Are there hot springs or volcanoes in this extreme environment ? Are there exchanges between the subsurface ocean and the organic-rich surface of the Orange Moon ?
Researchers are astonished to observe a remarkably high concentration of methane in Titan's atmosphere. That's quite surprising because methane tends to be broken down by ultraviolet light from the Sun over time. Are there internal sources likely to maintain or increase the level of methane observed in Titan's atmosphere ? Are there cryovolcanoes, cryovolcanic vents or deep cracks spewing methane ? Planetologists imagine that we could find geysers of ammonia rising from a salty underground ocean. The molecules can be broken down by solar radiations and the new compounds or elements can recombine to form new molecules such as methane. That's what is happening in the upper atmosphere with ultraviolet light which interacts with the environmental compounds. The subsurface ocean of the giant moon may host lifeforms if there are exchanges between the ground rich in organics or hydrocarbons and the subsurface ocean mainly composed of water even if the floor of this hypothetical ocean is completely frozen. Due to tidal forces, there may be cracks or hydrothermal vents on the floor of this liquid layer implying the presence of potential oases.
Researchers are particularly interested in the atmosphere of Saturn's largest moon because it looks like the atmosphere of the Early Earth and because it contains a haze rich in organics or hydrocarbons. Can this haze engender complex molecules or prebiotic molecules ? The environment of Titan may represent, in fact, a natural prebiotic laboratory. Planetologists have recently identified molecules which could form cell membranes for any organism present on Titan. Those relatively complex molecules which are useful in the production of plastics on Earth are vinyl cyanide or acrylonitrile. They are likely to engender stable or flexible structures similar to cell membranes. In 2015, some university researchers had identified acrylonitrile as the best molecule to form structures similar to the lipid bilayers of living cells we encounter on our planet. They imagined and modeled a microscopic sphere called the azotosome. This kind of sphere can play the same role as Terrestrial lipid bilayers on Titan. Michael Mumma who is director of the Goddard Center for Astrobiology pointed out : « The ability to form a stable membrane to separate the internal environment from the external one is important because it provides a means to contain chemicals long enough to allow them to interact.» He added : « If membrane-like structures could be formed by vinyl cyanide, it would be an important step on the pathway to life on Saturn's moon Titan.» Acrylonitrile appears to represent a relatively significant concentration of Titan's atmosphere since it represents a proportion of up to 2.8 parts per billion and it may be more abundant in the stratosphere at altitudes of at least 125 miles or 200 kilometers. Kraken Mare, Ligeia Mare or Punga Mare represent key places to look for exotic lifeforms on Titan.
During its mission, the Cassini spacecraft will have performed 127 close flybys of Saturn's largest moon. We've managed to determine that most lakes, seas and rivers were intriguingly located in the high latitudes of Titan. The north polar area appears to be the most humid region of Titan today. Dynamic clouds composed of hydrocarbons have been seen in the areas where lakes or seas are found. Some elongated clouds have been observed at lower latitudes as well. Those clouds may produce rainfall of methane likely to darken the surface. We've obtained radar data of Titan's surface representing about 67 percent of the surface area of the giant moon. We've combined radar data, near-infrared or infrared data to improve our understanding of Titan's landscape. Steve Wall who is deputy lead of Cassini's radar team at NASA's Jet Propulsion Laboratory in Pasadena, California pointed out : « Now that we've completed Cassini's investigation of Titan, we have enough detail to really see what Titan is like as a world, globally.» Planetologists try to have a clear view upon the dynamics of surface liquids on Titan. Are there long-term or seasonal migrations of methane or ethane from pole to pole ? Researchers have been surprised to notice that the Summer clouds in the high latitudes of the northern hemisphere are relatively sparse.
Elizabeth Turtle who is a Cassini imaging team associate at Johns Hopkins Applied Physics Laboratory, Laurel, Maryland argued : « The atmosphere seems to have more inertia than most models have assumed. Basically, it takes longer than we thought for the weather to change with the seasons.» That's why some scientists have envisaged the hypothesis of an underground reservoir of methane or the hypothesis of a subsurface ocean of methane. Elizabeth Turtle added : « There isn't a global reservoir at the surface, so if one exists in the subsurface that would be a major revelation about Titan.» The last close flyby of April 22, 2017 over Titan showed, via radar data, that the famous « Magic Island » was absent implying that the bright dynamic patch might have been related to bubbles or waves. Radar data taken on the last close flyby of the Opaque Moon can be compared to radar data obtained at the beginning of the mission in 2004 since some areas had already been observed in 2004. Steve Wall pointed out : « It's pretty remarkable that we ended up close to where we started.» He concluded : « The difference is how richly our understanding has grown, and how the questions we're asking about Titan have evolved.» Titan clearly appears to be a dynamic world.
The diagram above shows several moons of Saturn which represent an exobiological interest. The moons appear at the same scale. From left to right, one can observe the icy moon Enceladus, the cratered moon Tethys, the Hazy Moon Titan and the two-toned moon Iapetus. The view of Enceladus is based on an image acquired from the Cassini probe on November 27, 2016. The view of Tethys is based on a mosaic produced via images taken from the Cassini spacecraft on September 24, 2005. The view of Titan is based on a view generated via images obtained from the Cassini orbiter on January 30, 2012. The view of Iapetus is based on a mosaic generated via images captured from the Cassini spacecraft on September 10, 2007. Montage Credit: Marc Lafferre, 2017.
The image above reveals two views of Titan's disk taken with the Narrow-Angle Camera of the Cassini probe on March 21, 2017. The view of Titan at left corresponds to a natural-color image combining images captured using red, green and blue spectral filters. The view of the Opaque Moon at right represents a false-color image produced by substituting an infrared image sensitive to wavelengths centered at 938 nanometers for the red color channel. One can notice elongated clouds at high latitudes in the northern hemisphere as well as the presence of pools of liquid hydrocarbons in the north polar region. Image Credit: NASA/JPL-Caltech/Space Science Institute.
- To get further information on that news, go to: https://www.space.com/37721-saturn-moons-alien-life-nasa-cassini.html, https://saturn.jpl.nasa.gov/news/3095/nasa-finds-moon-of-saturn-has-chemical-that-could-form-membranes and https://saturn.jpl.nasa.gov/news/3099/cassini-prepares-to-say-goodbye-to-a-true-titan.
July 29, 2017 : New Studies Reveal the Surprising Finding of Carbon Chain Anions and Vinyl Cyanide Molecules That Could Engender Cell Membranes in the Titanian Atmosphere
Researchers are fully aware that the atmosphere of Saturn's largest moon Titan unveils a captivating chemistry involving carbon or organics. Titan's atmosphere which appears orange or brown is deep, thick and completely opaque in the visible spectrum due to the presence of a haze engendered by numerous chemical reactions in the air and in particular in the upper atmosphere of the giant moon where ultraviolet light from the Sun plays a key role. The atmosphere of Titan is mainly composed of nitrogen or molecular nitrogen like the atmosphere of the Earth. Methane is the second most abundant compound of the atmosphere of the giant moon. Oxygen is absent or quasi-absent in the atmosphere of Titan. A complex haze made up of organics engendered by interactions between elements or molecules in the upper atmosphere and ultraviolet radiations from the Sun can be noticed in the Titanian atmosphere.
The atmosphere of Saturn's largest moon probably looks like the atmosphere of the Early Earth before life emerged or oxygen developed. The complex chemistry occurring in the air on Titan on the basis of organics, hydrocarbons or nitrogen draws the whole attention of researchers who regard Titan as a natural prebiotic laboratory or a natural laboratory to understand the development of organics from simple molecules to more complex molecules involving carbon. There is a methane cycle on Titan unveiling lakes, seas, rivers or clouds like on Earth with the water cycle. Can an exotic lifeform emerge in an environment similar to that of Titan ? Are there exoplanets harboring seas or oceans of methane or ethane where an exotic lifeform can develop ? The environment of Titan may help us answer these questions.
The atmosphere of the Opaque Moon is protected, to a certain extent, by the magnetic field of Saturn against solar winds. However energetic particles from our star or from the environment of Saturn can reach the Titanian atmosphere and engender chemical reactions within the upper atmosphere. Special combinations between nitrogen, hydrogen and carbon can take shape and complex molecules or even prebiotic molecules can emerge in this photochemical soup encountered in the upper atmosphere of Titan. Some molecules which are massive or complex enough will tend to go down toward the surface and produce the haze, the fog or the smog that we see and that contains organics. The dynamics of the haze and the process which starts with elements or simple compounds and which ends with remarkably complex compounds are hard to analyze.
A new study unveiled in Astrophysical Journal Letters, entitled « Carbon chain anions and the growth of complex organic molecules in Titan's ionosphere » and proposed by R.T. Desai reveals the detection of carbon chain anions in the environment or in the complex atmosphere of Titan, thanks to data from the Cassini spacecraft. Researchers were astonished to identify that type of negatively charged molecule due to its high level of reactivity which should prevent it from lasting a long time in the hazy atmosphere before combining with other compounds or molecules. Scientists become aware that Titan's atmosphere is even more complex than we had thought. We can revise some theories regarding Titan's atmosphere. The molecules identified represent linear molecules which can act as building blocks for more complex molecules or organics which are fed by low-mass molecules or intermediate-mass molecules. The negatively charged species that we have detected may even have led to the development of the early forms of life on our planet.
Planetologists were able to notice the presence of the carbon chain anions on the basis of CAPS or Cassini's plasma spectrometer as the spacecraft was evolving through the upper atmosphere of the Opaque Moon at an altitude ranging from 950 km to 1300 km above the ground of Titan. The data obtained from the Cassini orbiter revealed that the carbon chains became depleted closer to Titan, while precursors to bigger aerosol compounds experienced rapid growth, implying a close link between the two, with the chains fuelling the bigger compouds. Ravi Desai of University College London and who led the analysis advanced : « We have made the first unambiguous identification of carbon chain anions in a planet-like atmosphere, which we believe are a vital stepping-stone in the production line of growing bigger, and more complex organic molecules, such as the moon's large haze particles.» He argued : « This is a known process in the interstellar medium, but now we've seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules.» He added : « The question is, could it also be happening within other nitrogen-methane atmospheres like at Pluto or Triton, or at exoplanets with similar properties ?». Let's point out that the atmosphere of Pluto or Triton is much less dense than that of Titan. The atmospheric pressure on Titan's surface is higher than that of the Earth at sea level. The Titanian environment appears favorable to chemical reactions.
Andrew Coates who is also from the University College London, who collaborated in the study and who is a co-investigator of CAPS pointed out : « The prospect of a universal pathway towards the ingredients for life has implications for what we should look for in the search for life in the Universe.» He added : « Titan presents a local example of exciting and exotic chemistry, from which we have much to learn.» Thanks to the Huygens probe which landed onto the surface of Titan on January 14, 2005, we've captured aerial views or images of the soil taken from the surface of the Opaque Moon. The Cassini orbiter allowed us to identify lakes, seas and rivers at high latitudes on Titan. We know we have to go back to Titan into the land of lakes, seas and rivers. The Cassini probe will crash into Saturn in less than two months and we have to prepare new ambitious missions. The James Webb Space Telescope and ESA's Plato exoplanet mission will probably help us monitor the evolution of Titan's climate and meteorology. They will also help us study the atmosphere of exoplanets. An advanced ground-based facility like ALMA is likely to enable follow-up observations of the dynamics and the chemistry of Titan's atmosphere.
Nicolas Altobelli who is ESA's Cassini-Huygens project scientist argued : « These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how complex organic molecules are produced in an early Earth-like atmosphere. » He added : « While we haven't detected life itself, finding complex organics not just at Titan, but also in comets and throughout the interstellar medium, we are certainly coming close to finding its precursors.» Titan may host significant clues regarding the mechanics of complex carbon-based molecules or the development of prebiotic compounds. Planetologists, enthusiasts or explorers are eager to see the lakes, seas or rivers of Titan because the scenery may be captivating or intriguing and because they may represent a soup of complex molecules, prebiotic molecules or even lifeforms. Can you imagine a sea of methane ? If there are lifeforms on Titan, they are not based on liquid water but on liquid methane or liquid ethane because the average environmental temperature is much too low for the presence of liquid water on the surface. The environmental temperature is around minus 180 degrees Celsius, minus 290 degrees Fahrenheit or 93 Kelvin at sea level on Titan.
A new study unveiled online on July 28, 2017 in the journal Science Advances , entitled « ALMA detection and astrobiological potential of vinyl cyanide on Titan » and led by Maureen Palmer, of NASA's Goddard Space Flight Center in Greenbelt, Maryland, reveals that the thick and deep atmosphere of Saturn's largest moon contains a large amount of vinyl cyanide molecules which may potentially form cell membranes for hypothetical organisms in the hydrocarbon-rich seas or lakes of Titan. The cell membranes we know on Earth are composed of fatty molecules called lipids. We can't imagine the same type of cell membrane on Titan because the environmental temperature is far too low as the researchers explain. Nevertheless, computer simulations demonstrate that vinyl cyanide whose chemical formula is C2H3CN has the potential to form membranes in the harsh environment of the Orange Moon. Until now, on the basis of data from the Cassini probe, we had gathered hints of the presence of this particular molecule in the Titanian atmosphere. The new study unveils that we have identified vinyl cyanide in Titan's atmosphere thanks to analyses of data captured in 2014 by the Atacama Large Millimeter/submillimeter Array (ALMA) which is a network of radio telescopes in northern Chile.
There may be large quantities of vinyl cyanide in Titan's environment as the work based on the ALMA data and computer modeling implies. The molecule may have migrated down into Titan's seas or lakes to form approximately 10 million membranes per cubic centimeter of liquid as the collaborators of the study advance. One has to keep in mind that coastal ocean waters on our planet harbor approximately 1 million bacteria per cubic cm of water. Obviously, the topic of life on Titan is more based on speculation or intuition than based on scientific clues. Maureen Palmer pointed out : « It's definitely a rough estimate, because there are just so many things we don't know about Titan.» She argued that while the new research work helps fill in « a tiny sliver of the habitability puzzle » for the Opaque Moon, it is likely to help researchers have a better understanding regarding the chemical reactions taking shape in the atmosphere of the giant moon. She pointed out : « It can help lead us along to a better understanding of Titan's chemistry and what sort of increasingly complex molecules can be found there. » Planetologists can notice that Titan's atmosphere is an active environment of chemical reactions like our own environment. Photochemistry via ultraviolet light from the Sun in the upper atmosphere engenders a natural « lego game » involving methane, nitrogen, ethane or acetylene.
The image above corresponds to a natural color view of Titan's upper atmosphere where photochemistry closely related to ultraviolet radiations from the Sun plays a key role. Methane molecules present in the upper atmosphere are being broken apart by UV light from our star and engender new molecules or compounds via new connections with other elements or molecules like molecular nitrogen, ethane or acetylene. Heavier molecules will go down toward the soil of the giant moon. A haze of organics or hydrocarbons can be clearly noticed on Titan. The view was generated on the basis of images acquired with the Wide-Angle Camera of the Cassini probe using red, green and blue spectral filters on March 31, 2005. Image Credit: NASA/JPL/Space Science Institute.
The radar view of Titan's surface above represents a portion of a swath obtained with the Radar Mapper of the Cassini spacecraft on May 22, 2012 during the T83 Flyby. One can notice several lakes found at high latitudes in the northern hemisphere of the Opaque Moon. One can notice the action of erosion as well. The area was experiencing the Spring Season at the time of the observation. Are there complex organics, prebiotic molecules or even organisms within those lakes ? Image Credit: NASA/JPL/Jason Perry/Cassini RADAR Team.
To get further information on that news, go to: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Has_Cassini_found_a_universal_driver_for_prebiotic_chemistry_at_Titan, http://iopscience.iop.org/article/10.3847/2041-8213/aa7851, https://www.space.com/37653-saturn-moon-titan-cell-membrane-molecules.html and http://advances.sciencemag.org/content/3/7/e1700022.
July 20, 2017 : A New Analysis Reveals The Potential Ways To Exploit Or Generate Energy For Any Human Colony On Titan
A new study published in the Journal of Astrobiology & Outreach, entitled « Energy Options for Future Humans on Titan » and proposed by Amanda R. Hendrix and Yuk L. Yung, unveils the potential ways to exploit or produce energy on Saturn's largest moon Titan. The Opaque Moon which resembles the Early Earth has a significant atmosphere dominated by molecular nitrogen and methane. This atmosphere engenders winds which are strong enough to sculpt the landscape and generate linear and parallel dunes extending over long distances. In the high latitudes of the giant moon, there are multiple lakes, seas or rivers of hydrocarbons. At first sight, we can use, at least, the energy of Titanian winds and the energy of liquid methane or liquid ethane on the surface of Titan. In fact, the options to produce energy for years on the Opaque Moon are numerous, from the hydrogenation of acetylene to nuclear power, wind power, hydropower, the combustion of methane via electrolysis of the native water or even solar power. The energy from geothermal activity or geysers may also represent an option.
Currently, NASA, politicians, scientists or visionaries like Elon Musk who runs the electric car manufacturer Tesla and the reusable rocket corporation SpaceX are preparing or imagining the technologies or the plans to send humans to Mars in a relatively near future. We have envisaged a human colony on the Moon or on Mars. But could we envisage a human colony in the Saturn System on Titan ? Saturn and Titan evolve about 10 times farther from the Sun than the Earth and it took the Cassini/Huygens probe approximately 7 years to reach the Saturnian System. If we can send much faster rockets, why not ! Cosmonauts may probably have to rely on nuclear power to resist the harsh environment of Titan since the energy received from the Sun is very weak in the System of the Ringed Planet. Titan is composed of a deep, thick and opaque atmosphere generating relatively weak greenhouse effects. The atmospheric pressure on the surface of the giant moon is higher than that of the Earth at sea level but much lower than that of Venus on the surface. One can notice that greenhouse effects are much stronger on Venus than on Earth or Titan.
The hazy atmosphere of Titan composed of hydrocarbons or organics may represent a natural prebiotic laboratory. The Orange Moon may even host signs of « life not as we know it. » NASA advances on its web platform : « In many respects, Saturn's largest moon, Titan, is one of the most Earth-like worlds we have found to date. » The agency also points out : « With its thick atmosphere and organic-rich chemistry, Titan resembles a frozen version of Earth, several billion years ago, before life began pumping oxygen into our atmosphere. » Water can't appear in its liquid form on the surface of the Opaque Moon due to the extremely low environmental temperatures. Water can only appear in its solid form on the surface of Titan. However, there may be a subsurface ocean of liquid water beneath the crust. Are there microbes, prebiotic molecules or extremely complex molecules on the surface of this fascinating moon ? Is there a biology related to liquid methane on Titan ? Oxygen is absent or quasi-absent in the Titanian atmosphere. Therefore, any cosmonaut visiting Titan won't be in a position to breathe the air of Titan.
The potential visitor will benefit from a relatively low gravity about 7 times lower than that of the Earth at sea level (about 14% of the gravity of the Earth at sea level) but he will have to face a denser air than usual for his movements. The smoggy atmosphere and the clouds of Titan will likely exert a protective effect against the radiations emanating from the Sun. The colonists won't have to fear solar radiations entering Titan's atmosphere since the radiation level will be much weaker than on Mars for instance. The cosmonauts will have several options to generate energy for their everyday life. Amanda Hendrix who is a staff scientist at the non-profit Planetary Science Institute said in a previous book that she co-authored and that is entitled « Beyond Earth: Our Path to a New Home in the Planets » that the Opaque Moon has huge deposits of hydrocarbons. We know that methane is widespread on Titan and that there are various types of hydrocarbons or organics in the Titanian environment. On Earth, we need hydrocarbons for heating or propulsion and we are conscious that oil reserves are limited. On Earth, hydrocarbons, petroleum or natural gas have, in principle, a biological origin. Data obtained from the Cassini spacecraft have allowed us to determine that Saturn's largest moon has hundreds of times more liquid hydrocarbons than the total amount of known oil and natural gas reserves on our planet.
The authors of the book « Beyond Earth: Our Path to a New Home in the Planets » advance that the explorers of Titan could produce energy from hydrocarbons if they use a separate combustion source in the absence of oxygen in the Titanian atmosphere. The new study proposed by Amanda Hendrix puts forward other ways of producing chemical energy, such as treating acetylene (C2H2) with hydrogen. Acetylene may be present in large amounts on the surface of the giant moon. Amanda Hendrix pointed out : « In this paper, I wanted to dig into the chemical energy options a bit deeper and also look into alternative energy possibilities.» She added : « My co-author, Yuk Yung, and I looked at chemical, nuclear, geothermal, solar, hydropower, and wind power options at Titan. The paper is designed to be a high-level first look at some of these topics.» She argued that, today, we have at our disposal the technology to produce energy on the basis of compounds present in the Titanian environment. However, she added that we could develop much more efficient technologies or ways to generate energy on Titan if we perform the appropriate study.
Regarding solar power or solar energy, we could produce more energy if we study the capabilities of different photovoltaic cell materials, in particular in an environment similar to the harsh environment of Titan. Some materials may indeed have a different behavior on Titan from that on Earth. That's why it appears crucial to study the materials in the right environment. Hydrology on Titan appears promising since there are large amounts of liquid methane or liquid ethane at high latitudes. The north polar region or the high latitudes of the northern hemisphere on Titan unveil a multitude of lakes, seas or rivers. As a result, we may use hydropower to generate energy or electricity like on Earth. The Cassini spacecraft has allowed us to obtain radar altimetry or radar data regarding some pools of Titan but we need a better mapping of the lakes, seas or rivers. We need to gather precise data regarding the depth, the topography or the flow rate of the drainage channels or the pools.
Amanda Hendrix is conscious of the great potential of hydropower or wind power. Radar data acquired from the Cassini orbiter have clearly shown the action of prevailing winds on the landscape in the dark areas of the low latitudes where Seif dunes or linear and parallel dunes extending over long distances can be well discerned. In the dense air of Titan close to the ground, winds can be strong. For an optimal use of winds, we would have to perform some studies into airborne wind turbines. Amanda Hendrix advanced : « I imagine that, as here on Earth, a combination of energy sources will be useful on Titan.» She added : « In particular, solar energy (using large arrays) and wind power (using airborne wind turbines) may be particularly effective. » The energy available for a small base or outpost would probably appear almost unlimited. Would it be better to live at low latitudes in the area of dunes or in the area of lakes, seas and rivers in the high latitudes of the northern hemisphere ?
Amanda Hendrix imagines, for instance, a bright future for colonists on Titan. Humans would not leave our planet for a one-shot mission or a relatively short mission with the goal of finding life, prebiotic molecules or complex molecules. They would go to the Opaque Moon for a long journey to build a base or an outpost which could generate power for years. One can imagine a scenario in which we would install solar arrays over 10 percent of the surface area of the Opaque Moon. Those solar arrays could engender a huge amount of energy or power corresponding to the power needs of a population of about 300 million persons that is to say the equivalent of the population of the United States. Amanda Hendrix pointed out : « This is just an initial estimate, of course, but what we're talking about is something much larger than a short-term human science mission to Titan. » Let's note however that the solar panels developed for Titan would have to be particularly efficient since the amount of solar energy received at the level of Titan is much smaller than that received by our planet.
The colonization of Titan is not for tomorrow since the next goal of major space agencies like NASA or ESA in terms of human travel is to put a foot onto the surface of Mars in a few years or decades. We are planning several missions to Mars in the coming years while the Cassini spacecraft is living its final weeks until the Saturnian crash of mid-September. Currently, researchers from NASA are preparing themselves for new missions to other worlds like Uranus, Neptune or the icy moon of Jupiter Europa. When will we have a new mission to Saturn and Titan ? There are budget constraints but the private sector and visionaries like Elon Musk or Jeff Bezos may help us accelerate the pace of exploration. Moreover, new players like the Chinese space agency or the Indian space agency could also perform great exploits regarding planetary exploration.
The image above represents a radar portion of Titan's surface in the high latitudes of the northern hemisphere which harbors numerous lakes, seas or rivers. The radar view was obtained from the Cassini spacecraft during the T29 Flyby of April 26, 2007. One can notice, in particular, several drainage channels where streams could be used to produce energy or electricity in the future. Explorers would have to find strong enough streams or falls in order to generate power via conventional methods. Image Credit: NASA/JPL/Jason Perry/Cassini RADAR Team.
The image above corresponds to an artist's impression of Titan's atmosphere and the Gas Giant Saturn on the horizon. The atmosphere of the Orange Moon is completely opaque from outer space preventing us from discerning landscape features in the visible spectrum. Landscape features on the giant moon can be identified in radar views and in infrared or near-infrared images. The hazy atmosphere of Titan is deep, thick and composed of several gas layers. Image Credit: Marc Lafferre, 2013.
- To get further information on that news, go to: https://www.seeker.com/space/exploration/future-space-colony-maybe-we-should-look-beyond-mars-to-saturns-titan-moon and https://arxiv.org/abs/1707.00365.
July 8, 2017 : A New Study Based On Radar Data Obtained From The Cassini Probe Shows That Lakes Or Seas On Titan Are Generally Quiet With Particularly Low Waves
A new research work entitled « Surface roughness of Titan's hydrocarbon seas », released in the journal Earth and Planetary Science Letters on June 29, 2017 and led by Cyril Grima, a research associate at the University of Texas Institute for Geophysics (UTIG) at Austin, confirms that lakes or seas on Saturn's largest moon Titan are generally calm with relatively small waves. The study which is based on a technique developed by Cyril Grima and which involves scientists at Cornell University, NASA's Jet Propulsion Laboratory and The Johns Hopkins University Applied Physics Laboratory was funded by NASA and the California Institute of Technology Jet Propulsion Laboratory. Prior to this study, some researchers had already revealed that lakes or seas on Titan appeared remarkably smooth or were surprisingly quiet. With a relatively limited gravity and a relatively dense atmosphere, we could have imagined strong or high waves but that is not the case, apparently.
The new analysis based on radar data taken from the Cassini spacecraft during the early Summer on the Opaque Moon shows that most waves on the lakes or seas of the giant moon may attain only about 1 centimeter high. The work mobilized data regarding the three major lakes or seas, Kraken Mare, Ligeia Mare and Punga Mare. The lakes or seas present in the high latitudes of Titan's northern hemisphere appear remarkably quiet probably implying relatively weak winds or a viscous liquid. Researchers need to better understand the dynamics of Titanian waves or the activity level of lakes or seas on Titan in order to develop a suited lander, boat, submarine or drone for a future mission toward the targeted lakes or seas on Titan. If the lakes or seas on the Hazy Moon are calm, it may be easier for us to study them. Apparently, Kraken Mare, Ligeia Mare and Punga Mare are good places for paddling but not for surfing. Cyril Grima, who works in a research unit of the UT Jackson School of Geosciences, pointed out : « There's a lot of interest in one day sending probes to the lakes, and when that's done, you want to have a safe landing, and you don't want a lot of wind.» He added : « Our study shows that because the waves aren't very high, the winds are likely low.»
Titan is the second world known to harbor stable lakes or seas on its surface in the Solar System. Titan appears to be the largest moon of the Ringed Planet Saturn and the second largest moon in the Solar System. Ganymede, the largest moon of Jupiter, is a little bit bigger than Titan but Titan is covered with a relatively massive atmosphere as opposed to Ganymede which is devoid of any significant atmosphere. The atmosphere of Titan which is completely opaque and which appears orange or brown from outer space is dominated by molecular nitrogen like our own atmosphere. Methane represents the second most abundant gas in the atmosphere of the Opaque Moon. A smog or a haze is present in the Titanian atmosphere and under the action of ultraviolet light, complex interactions or chemical reactions can take shape in the upper part of the gas blanket. That's why complex organics or hydrocarbons can be found in the atmosphere of the giant moon. The organics may fall toward the soil like snow and engender a brown or dark material known as tholin. Researchers want to study the chemistry of organics and hydrocarbons on Titan because it may bring us clues regarding the magic of life. Some researchers have speculated that Titan may have the ingredients for an exotic lifeform. Will we find linear polymers with an electrical charge on Titan ? Will we find prebiotic molecules ?
The atmosphere of Titan has a remarkable dynamics with a methane cycle. Clouds of methane or ethane can be regularly identified in the high latitudes of the Hazy Moon. Curiously, the north polar region appears to be the most humid area on Titan with a multitude of lakes, seas and rivers. Radar data, infrared or near-infrared data obtained from the Cassini spacecraft have allowed us to clearly identify the lakes, the seas, the islands or the drainage channels on Titan. Radar data have also shown that the crust is apparently composed of water ice. The bodies of surface liquid on Titan may be composed of methane and ethane. The exact composition of the lakes, seas or rivers has not been clearly determined but in the harsh environment of Titan, a few molecules can appear in their liquid form on the surface. Methane, ethane and propane can appear as a liquid on the surface of the Orange Moon. The lakes, seas and rivers may also contain dissolved nitrogen in their composition dominated by liquid hydrocarbons.
Precipitation processes involving methane or ethane occur on Titan. Rainfall fuels rivers, lakes and seas which will undergo evaporation processes. Clouds can take shape via condensation processes like on Earth. Liquid water can't exist on the surface of Titan due to the extremely low environmental temperature. If there are cryovolcanoes on Titan, there may be eruptions of water ice because some scientists believe that there may be a subsurface ocean of liquid water beneath the presumed icy crust. There may also be pockets of liquid methane beneath the crust. That's why some hypothetical cryovolcanoes may spew liquid methane or more complex hydrocarbons like ethane or propane, as well. Cyril Grima advanced : « The atmosphere of Titan is very complex, and it does synthesize complex organic molecules–the bricks of life. » He added : « It may act as a laboratory of sorts, where you can see how basic molecules can be transformed into more complex molecules that could eventually lead to life. »
Cyril Grima developed a technique known as radar statistical reconnaissance in order to study with a remarkable level of detail some key parameters of the surface such as the roughness level or the density level of the material. Cyril Grima started his work as a graduate student at the Université Grenoble Alpes in France. He pursued the development of his innovative technique as a postdoctoral fellow at UTIG. His method allows researchers to precisely measure the surface roughness on the basis of radar data. The technique of Cyril Grima has been mobilized to determine the snow density and the surface roughness of snow in Antarctica and the Arctic. It has also been used as a tool in the process of the landing site selection for InSight, the future probe proposed by NASA and designed to land on Mars very soon since the launch is expected to happen next year. Some scientists from NASA's Jet Propulsion Laboratory proposed Cyril Grima to apply his fruitful technique to the pools of liquids present on Titan in order to have a better insight into their dynamics or the mean size of the waves.
The team of Cyril Grima focused its attention on the three main bodies of surface liquids found in the high latitudes of the northern hemisphere that is to say Kraken Mare, Ligeia Mare and Punga Mare. Kraken Mare is by far the largest pool of liquid hydrocarbons in the northern hemisphere of Titan and even across the globe. Kraken Mare can be regarded as a sea since it appears larger than the Caspian Sea for instance. Cyril Grima and his collaborators analyzed radar data acquired from the Cassini orbiter during the early Summer season of the Orange Moon and were in a position to determine that waves across those seas or lakes are extremely small, reaching only approximately 1 centimeter high and 20 centimeters long. Alex Hayes, a co-author of the study who is an assistant professor of astronomy at Cornell University, argued : « Cyril's work is an independent measure of sea roughness and helps to constrain the size and nature of any wind waves.» He concluded : « From the results, it looks like we are right near the threshold for wave generation, where patches of the sea are smooth and patches are rough.»
The new determination of wave size on Saturn's largest moon can appear quite surprising since researchers had anticipated stronger or higher waves during the early Summer in the northern hemisphere. Planetologists believe that this period is the start of the windy season in the northern hemisphere of the Opaque Moon. The outcome unveiling tiny waves and made possible by the technique of Cyril Grima doesn't seem in line with the configuration that researchers had anticipated since stronger winds imply, in principle, stronger or higher waves within the lakes or seas. If the liquid of the lake or sea is particularly viscous like oil or asphalt, one can imagine that the lake or sea will appear remarkably flat or smooth with very small waves even if the environment is windy. The fact that the lakes or seas on Titan may be remarkably calm is rather a good news for the development of a future lander, boat, submarine or drone. Many questions remain regarding the liquids of the lakes and seas. Are there internal sources like cryovolcanoes or fractures ? What is the exact composition of the liquid ? Is there a fog or a haze over the surface of the lake or sea ? Is the liquid transparent ? Is the liquid viscous ? In that case, it could pose a problem for a future probe. Thanks to the Cassini spacecraft, we've performed big improvements in our understanding of Titan's climate and meteorology. Several projects to send a lander or a drone to the lakes or seas of Titan have been put onto the table up to now. Let's hope an ambitious mission to the exotic seas or lakes of Titan very soon !
The image above generated on the basis of radar images obtained with the Radar Mapper of the Cassini probe during its orbital dance in the Saturn System reveals the humid area of the northern hemisphere of Titan in the high latitudes. Cyril Grima and his team analyzed recent radar data of the area to determine the roughness level of the lakes or seas which produce remarkably small waves. The lakes or seas appear uniformly dark or unveil limited brightness variations. Multiple islands or drainage channels can be observed. Image Credit: Cyril Grima/The University of Texas at Austin.
The image above corresponds to a portion of a radar swath acquired from the Cassini probe during the T25 Flyby. One can clearly see a portion of a major pool of liquid hydrocarbons located in the high latitudes of Titan's northern hemisphere. The upper part of the view unveils a big island or peninsula. The dark and uniform area in the lower part of the image represents a portion of the sea known as Kraken Mare. A scale was incorporated into the original radar view. Credit for the radar portion of the original radar view: NASA/JPL/Jason Perry/Cassini RADAR Team. Credit for the scale incorporated into the original radar view: Marc Lafferre, 2017.
- To get further information on that news, go to: https://www.jsg.utexas.edu/news/2017/07/calm-lakes-on-titan-could-mean-smooth-landing-for-future-space-probes or http://www.sciencedirect.com/science/article/pii/S0012821X17303163.
June 16, 2017 : A Recent Study Demonstrates the Potential Influence of Tidal Forces Upon the Dynamics of the Presumed Subsurface Ocean of Enceladus and Titan
Researchers believe that Titan and Enceladus may contain a subsurface ocean like Europa, Ganymede or Pluto. Most Terrestrial or icy bodies in the Solar System are dominated by craters like Mercury, the Moon, Callisto, Tethys or Dione but several moons in the Outer Solar System may contain an internal ocean. We've discovered a young surface in the south polar region of the small icy moon Enceladus with fractures and geysers of water ice. Those observations imply the presence of pockets of liquid water beneath the south polar region or even the presence of a global subsurface ocean ? Titan is now known to host lakes and seas of hydrocarbons in the high latitudes. The environmental temperature is extremely low and water can only appear in its solid form on the surface of the giant moon. However, beneath the crust, a thin layer of liquid water may exist. Gravitational forces of Saturn and the other moons may significantly shake the interior of Enceladus or Titan.
The idea that Titan or Enceladus may contain a subsurface ocean of liquid water is captivating because the lifeforms that we encounter on Earth are based on liquid water. Tides may bring the energy for the potential development of life. Life requires energy for its growth, its reproduction, its movement or its development. Could there be life beneath the icy crust of Enceladus or beneath the crust of Titan ? We can only speculate about this fundamental question ! Planetologists try to determine the potential depth of the hypothetical subsurface ocean of Enceladus and Titan. They also try to determine or to calculate the amount of energy generated from tidal dissipation inside those enigmatic moons. The analytical work is far from being over and new studies with a more elaborate or complex modeling are needed in order to move forward regarding the dynamics of the hypothetical subsurface ocean.
A new study upon ocean tides or dissipation tides regarding Titan and Enceladus was recently released in the Journal Icarus (Volume 281, 1 January 2017). The analytical work led by Hamish Hay, a doctoral candidate in planetary science at the University of Arizona's Lunar and Planetary Laboratory, is entitled « Numerically modelling tidal dissipation with bottom drag in the oceans of Titan and Enceladus ». Hamish Hay collaborated with his supervisor Isamu Matsuyama to perform this study. The planetologists developed a model to simulate ocean tides in the interior of the icy moons Enceladus and Titan. Their model mobilizes bottom drag and Rayleigh drag to analyze ocean dissipation. Their model allows them to perform predictions upon the influence of tidal dissipation on the dynamics of the orbit of the two moons. Obliquity tides can greatly lower the outward movement of the orbit of Saturn's largest moon. The team of specialists tried to determine how Rayleigh (linear) drag which applies to smooth flows and bottom (quadratic) drag which is more active affect tidal dissipation. The flows in the hypothetical subsurface ocean of icy moons are thought to be active or turbulent.
Hamish Hay developed a relatively simple model in order to have a general idea upon the major mechanisms of tidal dissipation inside Titan and Enceladus and to check whether the numerical model was in line with the theoretical calculations from other researchers. He ruled out or neglected some key factors or parameters like the presence of an icy crust above the subsurface ocean. He considered a subsurface ocean whose thickness was uniform over the entire globe. A uniform thickness for Titan is an hypothesis which may not be very far from reality. However, for Enceladus which is largely smaller than Titan, this hypothesis may not be realistic since the subsurface ocean beneath the south polar region, where the fractures are found, may be deeper or thicker than in the rest of the icy moon. Hamish Hay is satisfied to see that the outcome of his model is consistent with the outcome of existing theory. He will have the opportunity, in the future, to improve his theoretical approach by incorporating more parameters or more complexity into his computer simulations. For instance, he will have to take into account the presence of an ice cap or spatial variations in the depth of the subsurface ocean.
The dissipated energy beneath the crust of the moon is closely related to variations in the distance between the moon and the planet during its orbital itinerary and the obliquity of the moon or the tilt of the rotation axis of the moon relative to the normal of its orbital plane around the planet. In other words, the gravitational force exerted by Saturn will increase when the moon gets closer to the Gas Giant during its orbital dance and will diminish when the moon goes away from the Ringed Planet. The orbit around Saturn is not perfectly circular. The orbit of Enceladus or Titan around Saturn is elliptical implying variations in the amount of tidal forces undergone by them. The interior of the moons is shaken and the energy must be dissipated. Hamish Hay and his collaborator incorporated, in turn, the factor related to variations in the distance between the moon and the planet as well as the obliquity of the moon into their numerical model. In parallel, they made the depth or the thickness of the presumed subsurface ocean vary. They also changed the drag coefficient, a numerical approach of the fluid's resistance, to observe how the quantum of energy dissipated is affected.
Hamish Hay and his supervisor started their analytical work of tidal forces with the Opaque Moon Titan. They modified the parameter of the moon-planet distance which mechanically implies variations in the tidal forces exerted by Saturn on Titan. The outcome of the model unveiled several spikes in energy dissipation for a shallow subsurface ocean with a depth or a thickness of only a few tens of meters. That's probably far from reality since the subsurface ocean of Titan is believed to be over 100 kilometers deep. If we consider a depth of that order, the real dissipated energy related to variations in the distance between Titan and Saturn is expected to be relatively low compared to the hypothesis of a particularly shallow subsurface ocean. When the team of planetologists studied dissipation related to the obliquity of Titan or to the tilt of the rotation axis of the Orange Moon, the outcome was quite different. If the subsurface ocean of Saturn's largest moon is at least 100 meters deep, the warming that takes shape is closely related to the amount of resistance the subsurface ocean faces as it flows. This phenomenon is known as the « bottom drag coefficient ». Hamish Hay pointed out : « This would mean the ocean is dissipating more energy than we expected otherwise.» He added : « Of course, this relies on the magnitude of the bottom drag coefficient, which I emphasize, we don't know.»
Regarding the small icy moon Enceladus, whose south polar region is clearly active as the images obtained from the Cassini spacecraft show, the model of Hamish Hay and his collaborator demonstrates that the warming, related to bottom drag and variations in the distance between the moon and the planet, takes shape more easily when the subsurface ocean is less than one kilometer deep or thick. However, that simulated depth may be far from reality since the depth or thickness of the subsurface ocean of Enceladus is thought to be much higher. Rayleigh drag doesn't trigger any significant amount of dissipated energy related to tidal forces. The obliquity of Enceladus is likely too limited to engender significant tidal dissipation since the obliquity of Enceladus is lower than that of Titan which is higher than that of the Earth for instance. That's why the energy produced inside Enceladus may be due to other factors such as the gravitational influence of Saturn and the other moons which varies over time. The orbital eccentricity of Enceladus is 0.0047 which implies tidal deformation during the orbital dance around Saturn.
Tidal forces help us understand the evolution or the dynamics of the moons over long periods of time. Tides can strongly influence the orbital evolution of moons in a large timescale. The orbits of the moons may become less and less elliptical or more and more circular over long periods of time under the action of tidal dissipation. The model of Hamish Hay and his collaborator reveals that, if the subsurface ocean of Titan is deep or thick enough, tidal dissipation may lower the speed at which the Opaque Moon is moving away from the Gas Giant Saturn. On the other hand, the model demonstrates that, with a very thin subsurface ocean, the giant moon Titan might migrate towards the Ringed Planet. However, that configuration may be far from reality since researchers believe that the subsurface ocean of Titan is particularly deep or thick. Hamish Hay thinks that it is premature to speculate or to analyze the potential consequences of an active subsurface ocean in terms of exobiology. His goal is to bring new clues to our understanding of the tidal environments of the small icy moon Enceladus and the giant moon Titan. If we know the nature of the subsurface ocean and the amount of tidal energy generated beneath the crust, we will be in a position to speculate on the development or the nature of any extraterrestrial lifeform. The Cassini probe proposed by NASA and ESA is expected to penetrate into Saturn's atmosphere in September 2017 preventing the probe from contaminating Enceladus or Titan in case there are still microbes on the spacecraft.
The image above reveals a natural color view of Titan in front of a portion of Saturn and its rings. The view was generated on the basis of images acquired using red, green and blue spectral filters. The three images were captured from the ISS Narrow-Angle Camera of the Cassini spacecraft on August 1, 2007 at a distance of about 2.4 million kilometers or 1.5 million miles from the Opaque Moon. One can clearly notice that Titan is completely opaque in visible light due to the haze or smog found in the deep atmosphere of the giant moon. The mean distance between Titan and Saturn is about 1,221,870 km but the apoapsis of Titan is almost 6 percent higher than its periapsis implying relatively strong tidal forces related to the gravity of Saturn. Image Credit: NASA/JPL/Space Science Institute.
- To get further information on that news, go to: http://www.astrobio.net/news-exclusive/tides-source-heat-icy-moons and http://www.sciencedirect.com/science/article/pii/S0019103516300239.
June 13, 2017 : Are the Enigmatic Mazes of Titan the Outcome of Dissolution Processes ?
Thanks to the Cassini mission, we know that Titan is composed of a varied landscape with dune fields, mountains, hills, canyons, rivers, lakes or seas. Some areas of Saturn's largest moon remain quite mysterious like the mazes or the labyrinth terrain. A mapping of the surface of the Orange Moon has shown that the mazes which are reminiscent of karstic terrain on Earth cover a little over 1 percent of the surface. Researchers want to figure out the mechanisms that generate those giant mazes that stretch for tens of kilometers. To a certain extent, a parallel can be drawn between the topographic or geographical labyrinths of Titan which were first identified in 2010 from the Cassini probe and geographical features located in Papua New Guinea, in China, in Cuba, in Australia, in Canada or even on Mars. Some new analyses reveal the size, the distribution of the labyrinth terrain on Titan and the potential mechanisms that engendered the enigmatic mazes of the Opaque Moon.
Scientists are aware that the geology and the chemistry of Titan are different from the geology and the chemistry of the Earth but they have noticed similarities in landscape features or erosional processes. The labyrinths of Titan may bring clues regarding the nature of the soil. Michael Malaska who is a Cassini team member and a planetary geologist at NASA's Jet Propulsion Laboratory in California pointed out : « When we first saw them, we knew the terrain was special.» He added : « Now we know pretty much where they all are.» Michael Malaska used his expertise to characterize the potential mechanisms which may have engendered the labyrinth terrain of Titan at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas, in March 2017. Thomas Cornet, another scientist who works at the Saclay Nuclear Research Center in France, modeled, at the same conference, how portions of the Titanian landscape might dissolve to generate the geographical mazes.
Planetology allows us to perform comparative analyses of landscape features in different worlds where the chemistry and the composition can be significantly different. We can gather precious clues regarding the dynamics of the environment and the chemical properties of surface features. The relatively small proportion of the landscape represented by the labyrinth terrain on Titan demonstrates that the composition of the soil is far from being uniform on the giant moon. Michael Malaska advanced : A lot of areas on Titan « look almost exactly like some of the places we have here on Earth. » The Arecibo telescope located in the island of Puerto Rico was constructed inside a sinkhole of a labyrinth terrain. The landscape where the radiotelescope is found is karstic and limestone caves have been produced via dissolution processes engendered by the action of water. That process also produces channels and sinkholes. The sinkhole of the radiotelescope can appear tiny compared to some landscape features of the labyrinth terrain on the Opaque Moon. Michael Malaska argued : « The ones on Titan are way bigger.» He also advanced that the sinkholes of Titan may be easily 10 times the size of the sinkhole where the Arecibo telescope is located.
The mazes of Titan may be closely related to precipitation or rainfall of methane or ethane. The mechanisms engendering the labyrinth terrain on Titan may resemble the well-known mechanisms engendering caves or sinkholes on Earth. The labyrinth terrain found in the polar areas or polar caps of Mars follows a different logic since there are no rainfalls of liquid water or liquid methane. The « Swiss cheese terrain » of Mars is likely related to sublimation processes involving carbon dioxide. Depending on temperatures, carbon dioxide can appear as a gas or as a solid. Carbon dioxide can't appear in its liquid form in the environment of Mars. Carbon dioxide won't melt before evaporating. The cheese-like terrain may be engendered via sublimation processes. Sublimation of carbon dioxide ice implies that carbon dioxide goes directly from its icy form to its gassy form. Can a sublimation process take shape on Titan where the atmosphere is very dense ? Since the nature of the soil has not been determined, the hypothesis of sublimation which appears as a weak hypothesis can't be ruled out.
A radar view of the Opaque Moon captured from the Radar Mapper of the Cassini probe during the flyby of December 20, 2007 revealed a particularly eroded or rugged terrain with sinuous channels implying the action of liquids. The huge network of ridges, valleys and channels appearing as a labyrinth terrain on Titan corresponds to an elevated plateau which has been sculpted or carved away over geological time. Michael Malaska argued that some valleys which appear open and interconnected may be the outcome of flowing liquid. Like on Earth, rainfall can occur on Titan but the clouds are made of methane or ethane rather than water which can only appear in its solid form on the ground due to very low environmental temperatures. Some valleys are isolated or not connected probably implying a different process from typical processes. As the distance between the ridges increases, the mazes evolve from sculpted or cut plateaus to narrow valleys. Farther, one can find more individualized hills.
Michael Malaska who contributed to the classification work upon the different labyrinths found on the Orange Moon believes that the mazes may have been generated by dissolution processes related to liquid methane or liquid ethane which can interact with the organics of the ground and dissolve them to engender channels or valleys. That's a process which may resemble the dissolution process found on Earth in the limestone terrains where liquid water from rainfall, lakes or rivers can seep into the soil, dissolve the rocks and engender caves or networks of subsurface channels or rivers. Some researchers believe that the labyrinth terrain on Titan may be rich in organics which can be dissolved by liquid methane or liquid ethane. Michael Malaska imagines a configuration in which the massive plains represented a huge single block composed of a multitude of minor pits at the beginning of the dissolution process. Progressively, under the action of liquid methane or liquid ethane related to precipitation in particular, some interactions between the liquids and the ground take shape generating strong dissolution processes and the pits slowly increase in size, carving away at the surface. The labyrinth terrain that we can see today may be the outcome of a sustainable dissolution process of a giant plain.
In fact, several hypotheses have been advanced to account for the geographical mazes on Titan. The hypothesis for dissolution processes appears indeniably strong. However, other hypotheses must be taken into account such as rainfall and wind which engender erosion. Rainfall and wind erode the landscape, rocks, mountains or hills via well-known processes on our planet. They engender labyrinths on our planet since they erode, carve or sculpt the rocks such as limestone. Similar processes may occur on Titan even if we don't know the exact composition of the Titanian soil and its precise interactions with liquid methane or liquid ethane. The hypothesis for sublimation processes is considered as well. Planetologists must imagine the potential materials of the ground which could sublimate or directly pass from a solid state to a gassy state. Some organics like acetylene or ethylene, which have been identified on Titan, may be some candidates acting in hypothetical sublimation processes. Sublimation processes play a key role in the polar areas of Mars where carbon dioxide can sublimate but on Titan, environmental temperatures are extremely low and carbon dioxide may remain in its solid form. Michael Malaska thinks that massive sublimation processes may be unlikely in the area of the mazes because the conditions aren't right. Thomas Cornet argued : « Sublimation is quite difficult [on Titan] ».
Thomas Cornet and his collaborators performed a simulation upon the mechanisms of maze development on Titan under the potential influence of dissolution processes. They wanted to know how Titan's landscape might evolve and what it might look like over time if dissolution processes play a key role on the Opaque Moon. Thus, they adapted an Earth-based model for the particular environment of Titan dominated by hydrocarbons like methane and nitrogen. They were in a position to analyze the evolution of the presumed type of terrain found on Saturn's largest moon over millions of years. They were surprised at the outcome since the simulation reveals a striking resemblance with the Titanian features which have been observed from the Cassini probe. Thomas Cornet who presented the conclusion of his team at LPSC pointed out : « We know that dissolution should play a role in the landscape evolution.» The team of Thomas Cornet has had the opportunity to notice, on the basis of the simulation, that labyrinth topography could take shape within a few million years if there are rainfall rates similar to those on Earth. But nobody knows the real rainfall rate on Titan today and it may be largely lower than that of the Earth.
Michael Malaska believes that the mazes of Titan represent some of the oldest features on the Opaque Moon and that they may be billions of years old. This hypothesis implies, in principle, a relatively low rainfall rate. In fact, it is difficult to conclude since we still don't know the exact composition of the Titanian soil and we don't know the rainfall rate as well. The Cassini probe has collected an incredible amount of data regarding the topography or the atmosphere of Titan but our knowledge regarding the surface is clearly limited unfortunately. Thomas Cornet argued : « After 13 years, we don't have a clue [about the surface composition].» Michael Malaska pointed out : « That's actually one of the big outstanding mysteries.» The Huygens probe has revealed a wonderful panorama during its atmospheric descent on January 14, 2005 and the images of the soil suggest the presence of water ice and tholins. However, we've not analyzed the soil. We can mention however a release of methane during the impact of the probe. Michael Malaska advanced : « We saw the picture from Huygens of all that orange landscape, and we don't know what that is.» Let's hope new ambitious missions to Titan where we could send drones being able to study the intriguing places of Titan like the labyrinth terrain, the dune fields or the north polar lakes or seas.
The image above shows a rugged terrain on Titan and another rugged terrain found on Earth. The view on the left corresponds to a Synthetic-Aperture Radar image of Titan's surface acquired with the Radar Mapper of the Cassini spacecraft on June 7, 2016 during the T-120 Flyby. Dissolution processes may play a key role in the formation of that kind of labyrinth terrain on Titan. The view on the right represents a region called Gunung Kidul located in southern Java. This region also reveals topographic mazes. Their formation is closely related to erosion and dissolution since the area is limestone. There may be some similarities between the formation of those geographical features on Earth and the formation of topographic mazes on Titan. Image Credit: NASA/JPL-Caltech/ASI.
The image above represents a radar
view of Titan taken on December 20, 2007 with the Radar Mapper of the Cassini
orbiter during a flyby over the south polar region of the Opaque Moon. The
view is centered near 76.5 degrees south latitude and 32.5 degrees west
longitude. One can notice the impact of flowing liquids on the formation of
the landscape in that area. A lot of irregular valleys and mountains or hills
can be noticed. Liquid methane or ethane may engender strong erosional
processes and dissolution processes in the area. Image Credit:
|The image in the upper part of this
table reveals an artistic view of a labyrinth terrain on Titan. The landscape
was generated by using the Shape From Shading Technique on the basis of a
radar image obtained on December 20, 2007 from the Radar Mapper of the Cassini
probe during a flyby of Saturn's largest moon over the south polar region. One
can notice sinuous channels suggesting the presence of ancient river flows.
The nature of Titan's soil remains quite mysterious but some areas may act in
a similar way to limestone on Earth under the action of liquids. The view in
the lower part of this table shows the portion of the original radar view used
to produce the simulated image of Titan's landscape. An arrow was incorporated
into the radar view to indicate the orientation of the virtual camera
capturing the simulated image.
Credit for the Artist's Impression:
Marc Lafferre, 2017.
- To get further information on that news, go to: https://www.space.com/37142-mystery-mazes-saturn-moon-titan.html.
June 10, 2017 : The Cassini/Huygens Mission Allowed Us To Rapidly Realize That Titan's Atmosphere Was Deeper Than Previously Believed
The Cassini orbiter is expected to perform a spectacular plunge into the atmosphere of the Gas Giant Saturn on September 15, 2017. Since the launch of the Cassini/Huygens spacecraft on October 15, 1997, an enormous amount of data regarding Jupiter, Saturn and its numerous moons has been collected via the Cassini/Huygens spacecraft. In order to reach Saturn, the Cassini/Huygens spacecraft relied on the gravity assist of several planets to accelerate and to find the correct path toward the Saturn System. Two Venus flybys occurred on April 26, 1998 and on June 24, 1999. A flyby of our planet occurred on August 18, 1999. A flyby of Jupiter, the largest planet in the Solar System, occurred on December 30, 2000. Then, the spacecraft continued its journey toward the Saturn System and the Saturn Orbit Insertion took shape on July 1, 2004.
The Cassini/Huygens spacecraft needed to reach a remarkable speed in order to attain the Outer Solar System. That's why the spacecraft had to use the gravity of several planets and the rocket had a relatively limited amount of fuel. The total weight of the Cassini orbiter and the Huygens probe with full tanks is 12,593 pounds or 5,712 kilograms. The Cassini/Huygens spacecraft is remarkably big since it is 22 feet or 6.7 meters high by 13.1 feet or 4 meters wide. Charley Kohlhase who used to be Cassini's Science and Mission Design Manager and who is now retired pointed out : « Cassini is a giant. » He added : « It's the size of a school bus.» The Cassini/Huygens spacecraft used the orbital momentum of Venus to gain speed relative to the Sun. During the flyby of Venus which is closer to the Sun than the Earth, the spacecraft accelerated and made Venus slow down in its orbit around the Sun but the decrease in speed is not perceptible or is ridiculously weak because the mass of the planet is overwhelmingly higher than that of the Cassini/Huygens spacecraft.
The speed of the Cassini spacecraft relative to the warm planet Venus didn't change during the flyby or gravity assist but it changed relative to the Sun since it had accelerated by 13,400 miles per hour or approximately 6 kilometers per second thanks to the flyby of April 1998. Charley Kohlhase argued : « There's no net speed gain relative to the assisting body.» The flyby of Jupiter was carried out relatively far from the Gas Giant compared to the flybys of Venus and the Earth but this gravity assist allowed the spacecraft to accelerate by approximately 4,500 miles per hour or 2 kilometers per second. The path based on the solution known as Venus-Venus-Earth-Jupiter Gravity Assist or VVEJGA was not a shortcut but it allowed the spacecraft to reach Saturn in almost seven years and in more than 2 billion miles or almost 3,5 billion kilometers swallowed for a planet that orbits the Sun at a mean distance of less than 1.5 billion kilometers. Charley Kohlhase advanced : « It was the only way.» He added : « Cassini's mass was so large that we couldn't have gotten to Saturn without VVEJGA.» And the Cassini/Huygens spacecraft has had a tiny influence on the speed of the planets it flew by to change its speed or orientation. Charley Kohlhase pointed out : « Jupiter was slowed down by about one foot per 10 trillion years.»
Over the past few years, the Cassini probe has visited multiple moons of Saturn from small icy moons like Mimas or Tethys to the Opaque Moon Titan. The cratered moon Phoebe, which is 130 miles or 210 kilometers wide, was the first major moon of the Ringed Planet encountered by the Cassini/Huygens spacecraft on June 11, 2004. The path for the flyby of Phoebe had been carefully calculated by researchers or engineers since any error can have significant implications in the real trajectory of the spacecraft. Thus, we obtained a sharp view of Phoebe for the first time. Several moons have intrigued or surprised researchers. Iapetus which is famous for its contrast between a bright side and a dark side drew our whole attention. The leading hemisphere of Iapetus is covered with a dark material comparable to charcoal. The trailing hemisphere is bright or white like snow. We captured remarkable views of the moon and we had the opportunity to admire the equatorial ridge. Scientists are wondering how the ridge formed. Is it related to tidal forces ? Is it the outcome of the collapse of an ancient ring system around Iapetus ?
Pan and Atlas, two tiny moons of Saturn, also have a circular ridge so that they look like raviolis or flying saucers. The ridge of those tiny moons is apparently composed of icy particles from the ring system of Saturn. Bonnie Buratti who is a senior research scientist at NASA's Jet Propulsion Laboratory pointed out : « At least three of Saturn's little moons have those little skirts.» She added : « And we wouldn't have known that without these flybys.» The icy moon Tethys which looks like Dione or Rhea has a particularity revealed by data obtained from the Cassini orbiter. In September 2005, data obtained from the Cassini spacecraft unveiled arc-shaped reddish streaks a few hundred miles long and a few miles wide on the surface of the cratered moon. Their nature remains a mystery since they are not found at the bottom of a crater or at the bottom of a fracture. They seem to have been softly painted, without any influence on the relief or topography. Are they coming from the interior of the moon or from outer space ? Bonnie Buratti argued : « The streaks look like they're painted on.» She concluded : « They are very, very mysterious.»
The small icy moon Enceladus became a star during the Cassini/Huygens mission because it unveils a permanent or quasi-permanent internal activity involving geysers of icy particles or water particles erupting from the « Tiger Stripes » or the fractures found in its south polar region. Tidal forces related to Saturn and the other moons may play a key role in the development or the dynamics of this surprising internal activity. Enceladus appears remarkably spherical despite its relatively small size and it shows two types of terrain, a young and smooth terrain where fractures are found and a cratered terrain which is older. We obtained incredible views of the Tiger Stripes in October 2008 when the Cassini spacecraft passed as close as 16 miles or 25 kilometers from Enceladus. We managed to gather precious data regarding temperature variations or the composition of surface features. Enceladus is part of those moons in the Solar System which may contain an internal ocean of liquid water.
Titan, which the largest moon of Saturn and the second largest moon in the Solar System behind Ganymede, the largest moon of Jupiter, played a key role in the trajectory or the path of the Cassini/Huygens probe during its tour around Saturn. It appeared as a major pillar in terms of gravity for trajectory changes of the spacecraft because the amount of fuel stored in the spacecraft is limited. By using the gravity assist of moons, we can save a significant amount of fuel for the rest of the mission. Brent Buffington who is a trajectory designer for the Cassini mission explained : « We use the gravity of Titan to change the trajectory of the spacecraft. » Engineers were in a position to make the probe accelerate or slow down and to change its trajectory via a gravity assist. Everything is calculated precisely so that the probe goes where we want it to go. However, at the beginning of the mission, researchers became aware that the Titanian atmosphere was deeper than previously believed. Brent Buffington argued : « Titan's dense atmosphere extended farther from the surface than we thought.» That's why a couple dozen Titan flybys were modified in order to respect a safety distance or to avoid risky gravity assists. Some flybys have been performed farther from the Opaque Moon than originally planned. Orbital mechanics is sometimes more complex than we could think. Brent Buffington advanced : « We think we know what we're going to encounter, but sometimes we're wrong and must adapt our strategies accordingly.»
The Cassini/Huygens mission has confirmed that we can't be disappointed with Titan. Infrared or near-infrared data and radar data obtained from the Cassini orbiter have clearly revealed seas, lakes and rivers in the high latitudes or the polar regions of the giant moon. There is a methane cycle on Titan involving evaporation processes, condensation processes, cloud formation and precipitation processes like on Earth. The bodies of surface liquids may be mainly composed of methane and ethane. We have found in the dark areas of the low latitudes Seif Dunes or linear and parallel dunes extending over long distances. We have found canyons, mountains or hills. Titan may harbor a subsurface ocean of liquid water like Enceladus, Europa, Ganymede, Callisto or Pluto. Can a familiar lifeform emerge in such an environment ? Can a lifeform based on methane emerge in the seas or lakes of methane ? Linda Spilker who is Cassini's project scientist pointed out : « Cassini has brought Saturn and its family of moons into our neighborhood, making them as familiar as your own backyard.» She concluded : « With Cassini's final heartbeat, our close personal connection to the Saturn system will be gone, but so much more remains to be discovered. We must go back ! » The extraterrestrial lakes and seas of Titan capture our imagination and may surprise us. Let's hope a drone, a boat or a submarine very soon to explore the mysterious seas or lakes found in the high latitudes of Titan's northern hemisphere !
The image above represents a natural color view of Titan, Dione and a portion of Saturn and its rings generated on the basis of several images acquired on May 21, 2011 from the Narrow-Angle Camera of the Cassini spacecraft. This image is the outcome of the combination of three views captured using red, green and blue spectral filters. Titan was moving at a distance of about 1.4 million miles or 2.3 million kilometers from the Cassini probe whereas Dione, which is much smaller than Titan, was moving farther at a distance of about 2 million miles or 3.2 million kilometers from the Cassini orbiter. One can clearly notice the opaque and hazy atmosphere of Saturn's largest moon Titan. Planetologists have managed to determine that the Titanian atmosphere was deeper than expected prior to the Cassini mission. Image Credit: NASA/JPL-Caltech/Space Science Institute.
The diagram above shows the path of the Cassini/Huygens spacecraft toward Saturn from its launch on October 15, 1997 to the Saturn Orbit Insertion on July 1, 2004. Venus, the Earth and Jupiter played a key role in this journey thanks to their forces of gravity which were used to accelerate and orientate the probe toward the Saturn System. The Cassini/Huygens spacecraft could not exclusively rely on its fuel to reach the final destination. That's why the trip was not a straight line. The Cassini probe is expected to end its long journey on September 15, 2017 with a crash into Saturn so that Titan or Enceladus won't have been contaminated, biologically speaking, by the spacecraft. Image Source: https://saturn.jpl.nasa.gov/news/3070/scenic-route-to-saturn.
- To get further information on that news, go to: https://saturn.jpl.nasa.gov/news/3069/a-tour-of-saturns-moons and https://saturn.jpl.nasa.gov/news/3070/scenic-route-to-saturn.
May 27, 2017 : A New Season Starts On Saturn And Titan Implying Meteorological Or Atmospheric Changes
The rotation axis of Saturn is more inclined than that of the Earth relative to the normal of its orbital plane. That's why Saturn and its giant moon Titan have seasons like the Earth. When the Cassini-Huygens spacecraft arrived at Saturn in 2004, Titan and Saturn were experiencing the Summer season in their southern hemisphere and the Winter season in their northern hemisphere. A Saturnian year or a Titanian year lasts almost 30 Terrestrial years and each season on Saturn or Titan lasts approximately 7 Terrestrial years. The last Equinox on Titan or Saturn occurred in August 2009 with the end of the Summer season in the southern hemisphere and of the Winter season in the northern hemisphere. The northern hemisphere of Saturn and Titan was entering the Spring season whereas the southern hemisphere of Saturn and Titan was entering the Autumn season. A new milestone has been reached in May 2017 with the Solstice. The northern hemisphere of Saturn or Titan is now experiencing the start of the Summer season whereas the southern hemisphere is experiencing the beginning of the Winter season.
What are the implications regarding the dynamics of the meteorology or the atmosphere of Saturn or Titan ? Researchers have been in a position to notice, during the long mission of Cassini, significant changes in the atmosphere of Titan and Saturn. Several remarkable outbursts of cloud activity, apparently related to seasonal factors, have been observed during the course of the mission on Titan. Infrared or near-infrared images of the south polar region, from the Cassini probe, showed dynamic and transient cloud systems or storms in 2004. After the Equinox of August 2009, in 2010, giant storms were observed at relatively low latitudes on the Opaque Moon. Recently, elongated cloud systems at high latitudes in the northern hemisphere and cloud patches in the north polar region have been clearly identified from the Cassini orbiter. Those atmospheric features demonstrate the influence of seasonal factors on Titan. However, planetologists have been quite surprised to notice that the seasonal dynamics of cloud activity toward the northern hemisphere is not as high as expected. They were expecting a faster process of cloud development since prevailing climate models had predicted that the cloud activity should have begun several years earlier.
Elizabeth Turtle who is a Cassini imaging team associate at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland argued : « Observations of how the locations of cloud activity change and how long such changes take give us important information about the workings of Titan's atmosphere and also its surface, as rainfall and wind patterns change with the seasons too. » We know that most lakes and seas on Titan are found at high latitudes, the north polar region being the most humid area. They are apparently closely related to a methane cycle on Titan. Researchers try to characterize the relationship or the interactions between the lakes and seas found at high latitudes and the development or dynamics of clouds. In 2013, views from Cassini unveiled a yellow vortex developing or a sudden and fast development of haze and trace hydrocarbons over the south polar region of the Opaque Moon. A giant cyclone had already been observed over the north polar region. Researchers inferred that the new atmospheric phenomenon was the outcome of a seasonal reversal in progress, characterized by a change in the direction of the main atmospheric circulation of Saturn's largest moon. A progressive movement of fresh hydrocarbons from the low latitudes to the south polar region was apparently taking shape since the area received less and less light from the Sun. Ultraviolet light from the Sun can destroy hydrocarbons like methane. In the Winter darkness of the south polar region, the hydrocarbons are protected from solar radiations and can develop.
The Solstice of May 2017 corresponds to the longest day of the Titanian year or Saturnian year in the northern hemisphere and to the shortest day of the Titanian year or Saturnian year in the southern hemisphere since the subsolar point is at the equivalent of our Tropic of Cancer. The last Summer Solstice in the northern hemisphere occurred in December 1987 since a Titanian year or Saturnian year is almost 30 Terrestrial years long. Every Solstice occurs every 15 Terrestrial years so that the next Winter Solstice in the northern hemisphere will be in April 2032. When the Cassini-Huygens spacecraft reached the Saturnian System in mid-2004, the northern hemisphere of Titan or Saturn was experiencing the Winter season whereas the southern hemisphere of Titan or Saturn was experiencing the Summer season. Researchers rapidly realized the importance of seasonal factors on Titan and the complexity of the methane cycle on Saturn's largest moon. The initial mission for the Cassini spacecraft was four years long from 2004 to 2008. The Cassini orbiter managed to study Saturn, its rings and numerous icy moons orbiting around the Gas Giant. The exploration process was extended from 2008 to 2010 with a mission known as the Equinox Mission. During the Equinox Mission, the Spring Equinox in the northern hemisphere occurred in August 2009 and we were in a position to watch the solar radiations striking Saturn's rings edge-on, engendering shadows that unveiled remarkable new ring structures.
The exploration of Titan required more data over time in order to better understand its atmospheric dynamics in particular. That's why the exploration process was extended from 2010 to September 2017. The extended mission was the Solstice Mission. Thus, researchers can monitor seasonal changes from Spring to Summer in the northern hemisphere. Linda Spilker who is Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California pointed out : « During Cassini's Solstice Mission, we have witnessed – up close for the first time – an entire season at Saturn. » She advanced : « The Saturn system undergoes dramatic transitions from winter to summer, and thanks to Cassini, we had a ringside seat. » During the Solstice Mission, we observed an enormous storm emerging and developing in the northern hemisphere of Saturn. We also noticed the disappearance of bluer hues that had persisted in the high latitudes of the northern hemisphere as hazes related to Spring time started to take shape there. The hazes engender opacity in the atmosphere of Saturn so that it is quite hard to discern atmospheric features as opposed to Jupiter where cyclones or atmospheric features are easy to discern.
Data obtained from the Cassini probe have clearly shown that the formation of hazes in the atmosphere of the Gas Giant is closely related to seasonal factors like temperature variations and changes in the chemical composition of the upper atmosphere of the giant planet. The planetologists have noticed that some of the trace hydrocarbon molecules or gases found there like ethane, propane and acetylene react more rapidly than others to the changing level of solar radiation over the course of the Saturnian year. They have also found that the atmospheric phenomena on Saturn were not progressive or gradual. They were astonished to observe sudden changes at specific latitudes like the emergence of the giant milky storm in the banded atmosphere where prevailing winds are extremely strong. Robert West who is a Cassini imaging team member at JPL explained : « Eventually a whole hemisphere undergoes change, but it gets there by these jumps at specific latitude bands at different times in the season. » From the Equinox of 2009 to the Solstice of 2017, the Sun climbed relative to the northern part of the rings of Saturn so that the solar radiations became more concentrated in the way they hit the rings. They could penetrate deeper into the rings and heat the compounds to the warmest temperatures observed there during the mission.
The solar radiation during the Solstice allows the Cassini instruments to unveil how compounds or particles clump together and to determine the composition of the particles hidden or found deep in the middle of the ring plane. Thus, researchers can determine whether there are differences in the composition of the molecules or materials located in the rings and can determine the structure of the ring system. Are there multiple layers of different composition for instance ? At Solstice, the rotation axis of the Ringed Planet is inclined toward the Sun. That implies that the planet and its rings are inclined toward the Earth as well. The particular geometry related to the Solstice allows the radio signal from the Cassini spacecraft to pass more easily with a better quality through the densest rings of Saturn. Researchers can collect higher-quality data regarding the ring materials there. During the Solstice Mission, planetologists kept a particular attention to the icy moon Enceladus which produces geysers from fractures in its south polar region. Winter darkness has reached the south polar region where the geysers of ice and vapor are located. As a result, the Cassini spacecraft can't take sunlit images of the south polar region of the small active world anymore. However, we can acquire clearer data regarding the heat emanating from the interior of Enceladus because there are no interferences with the solar radiations.
As a result, Cassini researchers have been in a position to monitor, without any difficulty, the temperature of the terrain in the area of the Tiger Stripes. The geologically active moon may contain a subsurface ocean of liquid water as the images obtained from the Cassini spacecraft and particles or molecules collected or sampled by the Cassini orbiter suggest. The Cassini mission is expected to end on September 15, 2017 with a final dive into Saturn's atmosphere at the end of the phase known as Grand Finale. Before that event, the Cassini spacecraft will have carried out a series of spectacular plunges between the Gas Giant and its icy rings over the course of 22 weeks from April 26 to September 15, 2017. We will have collected images of Saturn at the shortest distance ever. We will have taken detailed views of the rings and we will have more data to analyze the structure or the interior of Saturn and to answer the question regarding the origins of the rings.
The image above reveals an unusual development of multiple large cloud formations at a low latitude on Titan. The view was captured on October 18, 2010 with the ISS Narrow-Angle Camera of the Cassini spacecraft. At that time, the northern hemisphere of the Opaque Moon was starting to experience the Spring season since the previous Equinox occurred in August 2009. A Titanian season is much longer than a Terrestrial season so that the Spring season in the northern hemisphere was going to last up to May 2017. The image was produced on the basis of three views acquired with a filter sensitive to near-infrared radiation centered at 938 nanometers and on the basis of a view captured with a filter sensitive to visible light centered at 619 nanometers. Image Credit: NASA/JPL/Space Science Institute.
The diagram above unveils seasonal transitions on Saturn or Titan from May 1973 to April 2032. A Titanian year is almost 30 Terrestrial years and a Titanian season is about 7 Terrestrial years. In May 2017, we witness the Solstice which marks the transition from the Spring season in the northern hemisphere to the Summer season in the northern hemisphere. In the southern hemisphere, the Autumn season is ending and the Winter season is starting. Therefore, Ontario Lacus is in the dark. Image Credit: David Seal, NASA/JPL-Caltech.
- To get further information on that news, go to: https://saturn.jpl.nasa.gov/news/3065/cassini-looks-on-as-solstice-arrives-at-saturn.
May 19, 2017 : A New Comparative Analysis of Topography and Drainage Channels On Titan, Mars And The Earth Reveals that the History of Titan's Landscape Is Closer To That of Mars Than That of The Earth
Thanks to the huge amount of data captured from the Cassini probe since the start of the mission in 2004, we know that the environment of Saturn's largest moon Titan unveils familiar processes such as evaporation processes, condensation processes, cloud formation and rainfall. There are lakes, seas, rivers, drainage channels, canyons or mountains on Titan like on Earth. The pools of surface liquids on the Opaque Moon appear to be mostly found in the polar regions or in the high latitudes. In the harsh environment of Titan, water can't appear in its liquid form and the pools of liquids are composed of liquid methane and liquid ethane. The meteorology of Titan is dominated by methane whereas the meteorology of the Blue Planet is dominated by water. Therefore, the Titanian environment can appear familiar and exotic at the same time.
Titan is in fact the only extraterrestrial body known to host stable pools of surface liquids. Mars is devoid of any stable rivers, lakes, seas or oceans today but, in the past, the Red Planet may have harbored oceans or seas of water. One can clearly see canyons, fractures or ancient drainage channels on Mars today. The atmosphere of Mars is too thin to allow the presence of seas or oceans of liquid water. Thus, Mars appears to be a giant desert at the present time. A team of researchers from MIT and led by Benjamin Black, an assistant professor at the City College of New York and a former MIT graduate student, performed a comparative study upon the influence of the topography or the dynamics of the upper crust on the formation of drainage channels on Titan, Mars and the Earth in the recent geological past. Benjamin Black and his collaborators concluded that the geological mechanisms governing the development of rivers on Titan and Mars are relatively similar due to the absence or quasi absence of plate tectonics on Mars and Titan in the recent geological past. The geological mechanisms engendering rivers on Earth appear different from those taking shape on Titan and Mars because the Earth has been governed by plate tectonics in the recent geological past.
The outcome of the study, which is entitled "Global drainage patterns and the origins of topographic relief on Earth, Mars, and Titan" and which was partly funded by NASA, was recently published in Science. The Earth has been undergoing active plate tectonics implying the movement of various plates, collisions between plates, the development of hills or mountains, crustal distortions, subduction areas, separations of plates or ranges of volcanoes. The path of rivers is closely linked to topography or relief. For instance, the development of mountain chains on Earth or the dynamics of the crust will tend to deflect the path or the orientation of rivers or drainage channels. Benjamin Black and his collaborators noticed that the river networks on Titan and Mars don't follow the same logic as the river networks on our planet. Benjamin Black pointed out : « While the processes that created Titan's topography are still enigmatic, this ruled out some of the mechanisms we're most familiar with on Earth. » The group of researchers advances the hypothesis that the topography on Titan is closely related to variations in the thickness of the crust and to the dynamics of the crust, intimately linked to tidal forces from Saturn and the other major moons of the Gas Giant. Thus, the Titanian topography or the distorted crust will influence the path of rivers or the orientation of river networks.
The Red Planet Mars may have harbored rivers, seas or an ocean of liquid water early in its history as a giant canyon like Valles Marineris suggests. The channels, the canyons or the dried-up rivers that we can see today on Mars probably formed long ago. A volcano like Olympus Mons reveals that the conventional mechanisms of plate tectonics that we encounter on Earth have been absent on Mars. The major landscape features that we see today probably took shape very early in the history of Mars at a time of active volcanism and heavy bombardments of comets or meteorites. The channels or the canyons that we can identify on Mars today allow us to determine the way the topography, the landscape or the impact craters influenced the formation of the rivers or the networks of rivers. Taylor Perron who is an associate professor of geology in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS) and a collaborator in the study argued : « It's remarkable that there are three worlds in the solar system where flowing rivers have carved into the landscape, either presently or in the past. » He added : « There's this amazing opportunity to use the landforms the rivers have created to learn how the histories of these worlds are different. » Taylor Perron and Benjamin Black were accompanied in their analysis by former MIT undergraduate Elizabeth Bailey and scientists from the University of California at Berkeley, the University of California at Santa Cruz and Stanford University.
Thanks to radar data, infrared or near-infrared data obtained from the Cassini spacecraft, we know, now, that there are lakes, seas, rivers, canyons, fractures, dune fields, hills or mountains on the Opaque Moon. The dark areas found at low latitudes are dominated by Seif dunes shaped by prevailing winds for instance. One can conclude, on the basis of observations from the Cassini orbiter, that the lakes, seas and rivers of methane or ethane are mostly concentrated at high latitudes. Cyclones or transient and dynamic storms can take shape in the polar areas as well. The surface of Titan is far from being completely uniform. There are bright areas contrasting with dark areas or areas with a lower albedo. Radar data have been very useful in the study of the Titanian topography even if the resolution is not always extremely high. We've been in a position to obtain altimetric data and to measure the size of relatively high mountains for instance.
In order to better understand Titan's topography, the team of Benjamin Black drew a parallel between the channels on Earth and the channels on Titan and Mars. The history of the rivers on Earth and the drainage channels on Mars may bring clues in our analysis of the Titanian rivers. Plate tectonics, on Earth, is a major factor for the development of rivers. Mountains or hills can rise when two continental plates collide into each other. Rainfall engenders brooks or rivers which can be deflected by the relief. The liquids will go down and evolve toward the valleys around the mountains or hills. Seas can develop where two plates move apart. One has to imagine or anticipate the overall movement of plates over long periods of time to figure out the development of drainage channels. On Mars, the relief that we know may have acquired its major features a long time ago during the primordial accretion process and the well-known Late Heavy Bombardment. At that time, the meteorites engendered massive impact basins and giant volcanoes like Olympus Mons which is the largest volcano in the Solar System. The maps of Martian rivers and Terrestrial rivers are remarkably precise so that we can produce relevant analyses of the dynamics of rivers over long periods of time and we can apply that knowledge to the analysis of the dynamics of Titanian rivers over long periods of time as well. Benjamin Black advanced : « We know something about rivers, and something about topography, and we expect that rivers are interacting with topography as it evolves. » He added : « Our goal was to use those pieces to crack the code of what formed the topography in the first place. »
The group led by Benjamin Black selected, in their analytical work, several maps of rivers on the Earth, Mars and Titan. The river map of Titan was generated on the basis of data captured from the Cassini spacecraft. The scientists marked the direction of the streams or the apparent orientation of each river. Since the original resolution of each map was different, the team had to put each map at the same resolution. The resolution for the maps of the Earth and Mars were relatively high revealing remarkable topographic details and the resolution of Titan was relatively low because of the opaque, deep and hazy atmosphere of Saturn's largest moon in particular. It is hard to identify rivers on Titan in infrared or near-infrared views since only large surface features like craters can be identified. It is clearly easier to identify rivers in radar views. Therefore, the planetologists lowered the resolution of the topography on Mars and the Earth so that it is the same as that of the original view of Titan. Then, they superimposed the maps of the river networks to reveal differences in their directions and they marked every stream that seemed to flow downhill. They noticed that rivers sometimes seem to flow uphill due to the limited resolution which prevents us from observing hills or mountains. Any mountain or hill is likely to divert the path of a river.
When the planetologists obtained
statistics regarding the percentage of Titanian rivers that seemed to flow
downhill, they concluded that the dynamics of the topography and the rivers on
Titan was closer to that of Mars than that of the Earth. They also used
another criterion that they called « topographic conformity » and which
represents the level of divergence between a topography's slope and the
direction of a river's flow. They also came to the conclusion that the
Titanian topography is closer to that of Mars than that of the Earth. Taylor
Perron argued : « One prediction we can make is that, when we eventually get
more refined topographic maps of Titan, we will see topography that looks more
like Mars than Earth. » He advanced : « Titan might have broad-scale highs and
lows, which might have formed some time ago, and the rivers have been eroding
into that topography ever since, as opposed to having new mountain ranges
popping up all the time, with rivers constantly fighting against them. » The
team of Benjamin Black also tried to determine the impact of cratering related
to meteorites on the relief or the topography of Mars. The researchers
resorted to a model they had previously developed to evaluate the degree of
river erosion on Mars on the basis of different impact cratering histories.
They concluded that the pattern of river networks on the Red Planet, at the
present time, implies a limited influence of meteoritic impacts. In fact, the
largest impact craters may have formed at an early stage during the geological
history of Mars. The subsequent asteroids or meteorites colliding with the
surface of Mars engendered relatively minor impacts on the overall map or
topography of Mars. Taylor Perron insists on the importance of topographic
studies in the prospect of future missions to the surface of Titan. He
explained : « Any way of filling in the details of what Titan's surface is
like, beyond what we can see directly in the images and topography Cassini has
collected, will be valuable for planning a return. » The Cassini mission will
come to an end in a few months but researchers have at their disposal a large
amount of scientific data to analyze for a better understanding of the
landscape of the Orange Moon.
The image in the upper part of this table corresponds to a portion of a radar view of Vid Flumina, a drainage channel feeding Ligeia Mare, a major pool of liquid hydrocarbons located in the high latitudes of Titan's northern hemisphere. The view was acquired from the Radar Mapper of the Cassini spacecraft during the 87th close flyby of the Opaque Moon on September 26, 2012. The river, probably composed of ethane and methane, is reminiscent of the Nile River found on Earth. Several tributaries can be seen in this network of channels. The second view from the upper part of this table represents an aerial image of the Nile River without the natural colors. The third view from the upper part of this table shows a sinuous land found on Mars without the natural colors. The image of Mars is at the same scale as the image of the Nile River.
for the radar view of Vid Flumina: NASA/JPL-Caltech/ASI.
- To get further information on that news, go to: https://news.mit.edu/2017/rivers-titan-landscape-resembles-mars-not-earth-0518 and http://science.sciencemag.org/content/356/6339/727.
April 29, 2017 : A New Study Shows that Twilight On Titan Is Much Brighter Than Daylight
A new study led by Antonio Garcia Muñoz, a planetary scientist at the Technical University of Berlin, entitled « Titan brighter at twilight than in daylight » and published in the journal Nature Astronomy on April 24, 2017 reveals that Saturn's largest moon Titan is paradoxically brighter during twilight than during daylight. The deep and complex atmosphere of the giant moon of the Gas Giant Saturn surprises researchers since it appears much brighter during twilight than during daylight unlike anywhere else in the Solar System. The specialists analyzed data acquired from the Cassini probe regarding the hazy, smoggy and opaque atmosphere of Titan and studied them in different wavelengths of radiation ranging from ultraviolet light to visible and near-infrared light. Antonio Garcia Muñoz pointed out that they unexpectedly found that on the Orange Moon, « twilight is brighter than the dayside ».
Titan appears to be the only known moon in the Solar System to contain a significant atmosphere. The Huygens probe which landed on Titan at a low latitude on January 14, 2005 recorded an atmospheric pressure at the level of the surface of 1,467 hPa which is largely higher than the atmospheric pressure at sea level on Earth. On Titan, the atmospheric pressure at sea level is significantly higher than that of Mars, Triton or Pluto on the ground. It is quite surprising to observe that Ganymede, the largest moon of Jupiter, is devoid of any significant atmosphere whereas Titan which is a little bit smaller is covered with a significant atmosphere. Mercury, the smallest planet in the Solar System, has no significant atmosphere even if the cratered planet is more massive than Titan. Titan is in fact a little bit bigger than Mercury but is less massive due to its lower mean density. Titan may have the right combination of mass and environmental temperature to retain an atmosphere even if other factors may also play a key role. The atmospheric pressure on the surface of Titan could be compared to the atmospheric pressure found at the bottom of a swimming pool on our planet according to NASA.
The atmosphere of Titan is mainly composed of nitrogen like the atmosphere of the Earth but the second largest compound present in Titan's atmosphere is methane and not oxygen like in our atmosphere. A haze makes the Titanian atmosphere completely opaque in the visible spectrum. The interactions between ultraviolet light coming from the Sun and compounds found in the upper atmosphere of Titan engender new molecules such as hydrocarbons (methane, ethane, propane, acetylene...), nitriles (HCN...) or organics. The Titanian atmosphere is very deep and several atmospheric layers can be noticed in the upper atmosphere of the Opaque Moon. Titan is relatively light compared to our planet since it only represents approximately 2 percent of Earth's mass. Therefore, its gravity is largely lower than that of the Earth so that the envelope of gases hovering over the solid or liquid surface is less compressed than that of the Earth. The atmosphere of the Opaque Moon turns out to extend to an altitude 10 times higher than Earth's atmosphere that is to say nearly 370 miles or 600 kilometers into space according to NASA. In order to determine why the Orange Moon is so bright at twilight, the team of Antonio Garcia Muñoz studied how Titan's highly extended atmosphere scattered solar radiations.
Antonio Garcia Muñoz explained that due to the fact that the Titanian atmosphere is hazy and extends high up, at twilight, more radiation gets scattered onto the surface of the Orange Moon than it does during the daytime « at all wavelengths investigated ». He pointed out that, in reality, on the basis of computer models and data obtained from the Cassini spacecraft, twilight can be up to 200 times brighter than daytime. That is clearly uncommon. We need to figure out the configuration of Titan compared to the Sun in order to understand the phenomenon. The hemisphere of the moon directly facing the Sun corresponds to daytime whereas the hemisphere facing away from the Sun corresponds to nighttime. Twilight will be found at the boundary between both hemispheres. The haze particles of the relatively thick atmosphere of Titan tend to scatter solar radiations at a forward angle. In other words, solar radiations are deflected and keep moving into the same general direction. The calculations performed by the group of scientists demonstrate that it is possible that the thick and dense atmosphere of Satun's largest moon could scatter more radiation toward the twilight areas than the central daylight region, just like the data captured by the Cassini spacecraft reveal. Furthermore, since the atmosphere of the Orange Moon is highly extended toward outer space, a large amount of photons that would go right by the sides of a planetary body with a less-extended atmosphere orientates itself to the rim of the Sun-facing side of the Opaque Moon (above the twilight area).
Antonio Garcia Muñoz explained that the new discovery allows researchers to deduce or to have a better idea upon how much solar energy gets absorbed by the surface and the atmosphere of the Smoggy Moon. Scientists can also better understand the way seas and weather operate or interact with solar radiations. One can imagine or theorize the conditions that any potential lifeform on Titan, in the past, in the present or even in the future might face. Can humans withstand the particular conditions on Titan where the environmental temperature is extremely low, where the amount of sunlight is relatively small and where the dynamics of the seas or lakes may be bewildering ? The scientists also advance that similar increases in brightness may occur on distant exoplanets, that is to say planets found outside the Solar System around other stars. The light of the star passes through the atmosphere around the disk of the night side and reaches our telescopes on Earth.
Antonio Garcia Muñoz argued : « If one could eventually detect a similar optical phenomenon at an exoplanet, then we could reasonably guess that the exoplanet atmosphere shares some similarities with Titan's. In particular, we could probably guess that its atmosphere is extended and hazy.» Today, we have the ability to determine the mass, the size or the density of an exoplanet and we sometimes manage to identify the presence of an atmosphere or the main ingredients of the atmosphere of an extra-solar planet. But we find some limits in extracting new information or clues regarding the nature or composition of the atmosphere. Antonio Garcia Muñoz pointed out : « This is important, because determining the properties of exoplanet atmospheres is very challenging, » and identifying this effect or phenomenon could help « inform us of their main properties. » We have found new classes of planets outside the Solar System like Hot Jupiters but finding oxygen in the atmosphere of an exoplanet would be clearly a major milestone in the near future. If we discover an exoplanet with a brighter twilight than daylight, that may imply a deep atmosphere, a hazy atmosphere, or an atmosphere rich in hydrocarbons or organics.
Researchers are wondering what the origin of the methane present in Titan's atmosphere is because, over time, methane tends to be destroyed by ultraviolet light coming from the Sun. Are there internal sources to the atmospheric methane ? Are there cryovolcanoes or geysers spewing out methane or molecular nitrogen ? The complex atmosphere of Saturn's largest moon captivates our imagination with its hydrocarbons, its organics, its clouds and its numerous atmospheric layers. The dynamics of lakes and seas found in the high latitudes or in the polar regions of the giant moon may be closely related to seasonal factors. Variations in the distance between Titan or Saturn and the Sun may also engender changes in the dynamics of the meteorology. A Titanian year lasts almost 30 Terrestrial years and each Titanian season lasts approximately 7 Terrestrial years. Observations from the Cassini probe in the infrared or near-infrared spectrum have clearly shown that seasonal factors play a significant role in the meteorology. For instance, a polar vortex has been recently seen developing over the south polar region. It may continue to develop during the Winter season in the southern hemisphere.
Curiously, the low latitudes of Titan appear relatively dry since no lake or sea has been clearly identified in the equatorial or tropical regions. Prior to the landing of the Huygens probe into the Shangri-La/Adiri region, some scientists had believed that the dark regions found at low latitudes were in fact seas or oceans of liquid methane or liquid ethane. However, thanks to the aerial views acquired from the Huygens probe, we know that those regions are not currently filled with liquids. The radar images obtained from the Radar Mapper of the Cassini spacecraft have allowed us to determine that Seif dunes or linear and parallel dunes extending over long distances dominate the dark areas found at low latitudes. Lakes, seas and rivers are mostly found in the high latitudes of the northern hemisphere where Winter is about to start very soon. Researchers monitor the relatively high cloud activity in the area to understand the dynamics of lakes, seas and rivers in the area. Will there be a process of net evaporation in the region of Kraken Mare, Ligeia Mare and Punga Mare during the long Summer season which is about to start ?
The image above corresponds to a natural-color view of Titan revealing the disk of the Opaque Moon with a ring or a halo of atmospheric light. The view of Titan was obtained with the Narrow-Angle Camera of the Cassini orbiter on November 3, 2013 at a distance of about 2.421 million miles or 3.896 million kilometers from the Orange Moon. One can notice the blue layer found in the upper atmosphere of Titan. This layer found at a remarkably high altitude represents a haze blanket that scatters sunlight. Image Credit: NASA/JPL-Caltech/Space Science Institute.
- To get further information on that news, go to : http://www.space.com/36609-twilight-outshines-daylight-saturn-moon-titan.html or https://www.nature.com/articles/s41550-017-0114.
April 25, 2017 : New Data Gathered From the Cassini Probe During the Final Close Flyby of Titan On April 21, 2017
The Cassini spacecraft which entered the Saturnian System in mid-2004 with the Huygens probe has just performed the final close flyby of Saturn's largest moon Titan and is now starting a process known as the Grand Finale which consists in a set of 22 orbits around the Gas Giant Saturn. The final close flyby of the Hazy Moon represented the 127th close approach to the giant moon. The close pass occurred on April 21, 2017 at 11:08 p.m. PDT (Pacific Daylight Time) or on April 22, 2017 at 2:08 a.m. EDT (Eastern Daylight Time). The spacecraft came as close as 608 miles or 979 kilometers from the surface of the Opaque Moon. During this close encounter, the Cassini probe acquired images and other data regarding Titan and transmitted the data to Earth, the data traveling at the speed of light with a journey lasting more than one hour.
New radar images of the land of lakes in the north polar region or in the high latitudes of the northern hemisphere have been taken during this particular flyby. The lakes, seas and rivers are mostly concentrated in the high latitudes of the northern hemisphere. They are not made of liquid water since the environmental temperature is extremely low around minus 179 degrees Celsius, minus 290 degrees Fahrenheit or 94 Kelvin. The pools of surface liquids in the north polar region of the Hazy Moon are believed to be mainly composed of methane and ethane. For the final flyby, researchers planned to capture data regarding a region swept by the imaging cameras of the orbiter, but not by radar. The radar specialists also plan to use the new data to study or determine the depths and compositions of some of the small lakes in the high latitudes of the northern hemisphere for the first time which will be the last opportunity. They hope to gather new clues regarding the nature or the dynamics of a famous bright and dynamic feature known as the « Magic Island ».
The Magic Island was a bright and new feature identified, on the basis of radar data, within the north polar lake or sea Ligeia Mare close to the coast. The shape of the bright feature had apparently evolved, extended, diluted and disappeared or completely disappeared relatively rapidly. Was it a transient island ? Will it reappear ? Was it a kind of iceberg ? Was it the radar signature of a transient field of bubbles ? Was it the sign of a turbulent liquid with strong waves under the action of relatively powerful winds ? Was it the consequence of a hot spring or a cryovolcano beneath the lake or sea ? The coastline near the Magic Island is well defined in radar images. One can notice that it is particularly irregular with multiple peninsulas or bays. Erosional processes might be quite strong in the area. We need new radar views of this enigmatic region with a satisfactory resolution in order to gather key data or key clues regarding the nature of the Magic Island. Linda Spilker who is the mission's project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California pointed out : « Cassini's up-close exploration of Titan is now behind us, but the rich volume of data the spacecraft has collected will fuel scientific study for decades to come. »
The Cassini spacecraft is going to start the Grand Finale, the final chapter of its remarkable journey, with a series of 22 dives between the rings and the Gas Giant on April 26, 2017. The last flyby of Titan allowed the probe to use the gravity of the Opaque Moon to bend its path or to slightly change its orbit in order to go into the relatively small gap between the rings and the Gas Giant, instead of going outside Saturn's main rings. At the end of this long sequence, the Cassini spacecraft is expected to carry out a plunge into Saturn's atmosphere on September 15, 2017. One has to keep in mind that, during the Grand Finale, the probe will move at a high speed, at tens of thousands of miles per hour. Thanks to the close pass of Titan, the probe was put into orbit for the last chapter of the long mission. Earl Maize who is Cassini project manager at JPL advanced : « With this flyby we're committed to the Grand Finale. » He added : « The spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn's atmosphere on Sept. 15 no matter what. »
The Cassini spacecraft acquired a significant increase in velocity of about 1,925 miles per hour or precisely 860.5 meters per second relatively to the Ringed Planet from the close flyby with Saturn's largest moon. This close encounter allowed the probe to go onward and to attain the farthest point in its orbital path around the Gas Giant at 8:46 p.m. PDT or at 11:46 p.m. EDT on April 22, 2017. The farthest point represents the apoapse which corresponds to the location where each new lap of the probe around Saturn starts. Mathematically or technically, this apoapse represented the beginning of the Grand Finale orbits. People are eager to discover the close-up views of the rings and the atmosphere of the Gas Giant. That's why the first captivating event will occur on April 26, 2017 with the first ultra-close dive past the giant planet. The final flyby of the Orange Moon simply represented the starting point of the Grand Finale.
The first dive of the probe between the rings and Saturn is expected to take shape on April 26, 2017 at 2 a.m. PDT or 5 a.m. EDT. The orbiter will be out of contact during that process and for approximately a day afterward while it performs science observations from the close flyby of Saturn. The earliest time the Cassini spacecraft is expected to establish radio contact with our planet is 12:05 a.m. PDT or 3:05 a.m. EDT on April 27, 2017. Images and other data will start to be transmitted to Earth shortly after communication is established between the probe and the Earth. The navigation or the orientation of the Cassini spacecraft is carried out or monitored by Cassini's navigation team. The specialists are there to monitor the radio signal transmitted from the probe on a display in the Spaceflight Operations Facility at NASA's Jet Propulsion Laboratory. Following the close encounter with Titan, the team carried out a « cleanup maneuver » in which the orbiter fired its thrusters to adjust the trajectory so that it more closely matches the planned path. The Doppler shift in the radio signal of the Cassini spacecraft provides the information to the team regarding the behavior of the probe or changes in the orbital parameters. The specialists or the engineers are in a position to determine whether the maneuver brought the planned change in velocity, called delta-v.
The Cassini probe which was designed, developed and assembled by the Jet Propulsion Laboratory started its long journey in 1997 with the Huygens probe, launched with a Titan IVB/Centaur. The main part of the mission started in mid-2004 with the SOI or Saturn Orbit Insertion. The Huygens probe plunged into Titan's atmosphere and landed on January 14, 2015 revealing an exotic landscape with eroded stones or pebbles implying the presence of an ancient river or brook. The aerial views unveiled a dark or red plain and bright hills sculpted by dark fractures or drainage channels reminiscent of familiar landscapes on Earth. Researchers became aware that there are familiar meteorological phenomena on Titan involving evaporation processes, condensation processes, cloud formation and precipitation processes. Obviously, liquid water is absent on the surface of Titan. The liquids found on the surface of Titan are methane, ethane or mixtures of relatively simple hydrocarbons mixed with dissolved nitrogen. The atmosphere of Titan is mostly composed of nitrogen and methane is the second most abundant gas in the hazy atmosphere. A parallel can be drawn between the water cycle on Earth and the methane cycle on Titan.
Thanks to data acquired from the Cassini spacecraft, we've been in a position to study the dynamics and the composition of Titan's atmosphere. The meteorology of Titan appears clearly complex even if clouds are not widespread on Titan and are relatively scarce compared to clouds on Earth. Clouds on Titan are mostly found at high latitudes or in the polar regions. The dynamics of clouds is closely related to seasonal factors. Each season on Titan lasts about 7 Terrestrial years and a Titanian year lasts almost 30 Terrestrial years. Infrared or near-infrared views obtained from the Cassini probe and acquired during the Summer season in the southern hemisphere of the Opaque Moon had revealed for the first time in history an extraterrestrial lake of stable liquids at a high latitude in the southern hemisphere. This lake whose shape looks like a foot or a kidney is known as Ontario Lacus. Later, thanks to radar data obtained with the Radar Mapper of the Cassini spacecraft, researchers realized that most lakes and seas were mostly concentrated in the north polar region or in the high latitudes of the northern hemisphere. Kraken Mare, found in the high latitudes of the northern hemisphere, appears to be the largest body of surface liquids in the northern hemisphere and on Titan. Will the level or the size of the lakes, seas or rivers in the northern hemisphere diminish as the Summer season in the area develops, due to net evaporation processes ? Will there be more storms or more dynamic clouds ? Will Ontario Lacus grow or will its level increase due to more condensation processes during the Winter season in the area ? We need to study the Titanian atmosphere during a full year in order to figure out its complex dynamics.
|The three images of this table represent unprocessed
views or raw images of the Opaque Moon Titan, obtained on April 21, 2017 from the
Cassini probe during the final close flyby of Saturn's largest moon. The
upper view clearly unveils the low-albedo regions of Fensal and Aztlan
where Seif dunes shaped by prevailing winds are widespread. The
relatively dark regions which mark a sharp contrast with bright regions
in infrared or near-infrared views are mostly found at relatively low
latitudes. The dark and uniform areas located in the high latitudes of
the Orange Moon correspond to lakes or seas.
Credit for the Images: NASA/JPL-Caltech/Space Science Institute.
- To get further information on that news, go to : https://saturn.jpl.nasa.gov/news/3030/cassini-completes-final-and-fateful-titan-flyby.
April 19, 2017 : A New Study Based On a Numerical Model Reveals that the Magic Island Phenomenon May Be Related To Bubbles
A new study published online in the journal Nature Astronomy on April 18, 2017, entitled « Bubble streams in Titan's seas as a product of liquid N2 + CH4 + C2H6 cryogenic mixture » and led by Daniel Cordier, a planetary scientist at the University of Reims Champagne-Ardenne in France, reveals or confirms that the famous phenomenon of the « Magic Island » may be closely related to the presence of a stream of bubbles. Several radar images of the same area in the high latitudes of Titan's northern hemisphere have allowed us to clearly notice the appearance, the evolution and the progressive disappearance of a bright patch close to the coast of the well-known lake or sea Ligeia Mare. This remarkable radar phenomenon is known as the Magic Island Phenomenon. Was it really a transient island ? That seems unlikely.
Titan, which is the largest moon of the Gas Giant Saturn and the second largest moon in the Solar System, is clearly a surprising moon. Titan is bigger than the planet Mercury and is more than twice as wide as the Dwarf Planet Pluto. Most planetary bodies in the Solar System are devoid of any significant atmosphere. Despite its relatively low gravity, Titan is covered by a significant atmosphere which is completely opaque in the visible spectrum. In fact, the atmosphere of the Orange Moon resembles the atmosphere of the Early Earth. The atmosphere of Titan is dominated by molecular nitrogen like the atmosphere of the Earth today. But oxygen is absent or quasi absent in the Titanian atmosphere and there are no clouds of water on Titan because environmental temperatures are extremely low due to the low level of energy received from the Sun at the level of Saturn or Titan. On Titan, the second most abundant gas present in the atmosphere is methane and not molecular oxygen like in the blue atmosphere of the Earth.
Thanks to the Cassini/Huygens mission, we have been in a position to observe or identify clouds, seas, lakes, rivers, mountains or canyons on Titan. To a certain extent, the Titanian atmosphere appears quite familiar with evaporation processes of hydrocarbons, methane or ethane, condensation processes of methane or ethane, the formation of clouds or cyclones and rainfall of methane or ethane. A complex haze of organics or hydrocarbons appears in the Titanian atmosphere under the action of ultraviolet light received from the Sun. The ultraviolet radiation from our star engenders a « lego game » in the upper atmosphere of Titan where molecules break up, forming new molecules or elements which recombine to form new compounds or molecules. Methane, ethane, propane, hydrogen cyanide, radicals or organics can take shape in the upper atmosphere and progressively fall toward the surface where they will form a red or dark sludge or material called tholin.
Titan appears to be the only extraterrestrial world to harbor stable liquids on its surface. Researchers advance that the pools of liquids on the largest moon of the Ringed Planet may be mainly composed of a mixture of methane, ethane and nitrogen. The environmental temperature at sea level on Titan is low enough and the atmospheric pressure is high enough to allow the presence of liquid methane, liquid ethane or liquid propane on the surface of the icy moon. Nitrogen can't appear in its liquid form but it can be dissolved within the lakes, seas or rivers of hydrocarbons. Water can only appear in its solid form in the harsh environment of the Opaque Moon. There may be mountains dominated by solid water on Titan. The radar images obtained with the Radar Mapper of the Cassini spacecraft have clearly shown that the pools of liquids on Titan are concentrated in the high latitudes or in the polar regions of the giant moon. The lakes, seas or rivers appear uniformly dark in radar images contrasting with the radar signal of the islands or the surrounding terrain which appears brighter, less dark or irregular in terms of brightness.
The high latitudes of the northern hemisphere unveil multiple lakes or seas as well as islands and drainage channels filled with liquid hydrocarbons. The largest body of surface liquids appears to be Kraken Mare. Ligeia Mare appears to be the second largest pool of liquids in the north polar region and it can be regarded as a sea due to its significant size. The third largest body of surface liquids in the area is Punga Mare. Researchers obtained several radar images of the land of lakes and seas. Thus, they have been in a position to analyze the dynamics of the pools of liquids. In 2013, the area of Ligeia Mare drew the whole attention of researchers because they noticed what appeared to be a new island close to the coast on the basis of a radar image taken on July 10, 2013 from the Cassini probe. This presumed island didn't appear in a previous radar view of the same region acquired on April 26, 2007 from the Cassini spacecraft. A radar view taken from the Radar Mapper of the Cassini spacecraft on August 21, 2014 showed that the bright feature of the Magic Island had apparently changed in shape and dissolved. Later, a radar view of the same area of Ligeia Mare taken on January 11, 2015 from the Cassini probe unveiled that the bright feature of the Magic Island had apparently completely or almost completely disappeared.
Several hypotheses were advanced to account for the intriguing phenomenon of the Magic Island. Was it a kind of iceberg floating and dissolving over time ? Was it a material emanating from the soil of the pool where it detached, rose to the surface and dissolved ? Was it related to tidal forces and a change in the level of the lake or sea in that area ? Was it related to alien creatures or a colony of micro-organisms comparable to the colonies of plankton that we encounter on Earth ? Was it related to an alien civilisation ? Was it related to a strong fog ? Was it related to the presence of gas bubbles ? The lead author of the study, Daniel Cordier, pointed out : « The physical process behind this strange behavior was, up to now, absolutely not understood.» The dominant hypotheses have been the hypothesis for gas bubbles and the hypothesis for floating solids. A recent study led by Michael Malaska suggests, on the basis of laboratory experiments, that the appearance of the Magic Island may be related to the presence of nitrogen bubbles rising from the sea or lake.
The team of Daniel Cordier shows, on the basis of a numerical model, that the phenomenon of the Magic Island may correspond to a concentration of bubbles or a process of fizzing in an unstable sea or lake. Each bubble of this temporary field may be more than an inch or 2,5 centimeters wide. If we send a probe, a boat, a submarine or a drone into that area one day, we will have to adapt the design of the probe in order to improve its stability and to face the obstacle related to fizzing or bubbles. Daniel Cordier and his collaborators wanted to know how gases and liquids might behave in the exotic environment of Titan's seas or lakes dominated by methane, ethane or a mixture of methane and ethane. As a result, they developed computer models to simulate the potential interactions between methane, ethane and nitrogen. Their work was based, in part, on experimental data previously gathered by the oil and gas industry regarding the behavior of similar fluids undergoing a relatively strong pressure related to the depth of the lake, sea or ocean.
The study implies that surface fluids, on the Opaque Moon, are usually mixtures richer in methane or CH4 whereas deeper fluids are dominated by ethane or C2H6. There are also interactions between the surface liquids dominated by methane and nitrogen or molecular nitrogen of the atmosphere. Therefore, nitrogen may also represent a key compound of the surface liquid in which it may be dissolved and rise to the surface from time to time, depending on seasonal factors in particular. Winds or tides can engender significant waves or instabilities on the lake or sea engendering foam. Temperature changes, heating phenomena or cooling phenomena can also engender instabilities within the lake or sea. All those phenomena are likely to force the mixtures of surface liquid to flow downward. At a certain depth, the sinking mixtures may separate due to the increased pressure exerted downward. The separation process may engender the release of nitrogen gas bubbles which will then go up to the surface to produce a fizzing surface with a relatively high albedo in radar images. The phenomenon of the Magic Island may correspond to an area of high reflectivity closely related to a high concentration of bubbles or a transient fizzing.
The team of Daniel Cordier calculated that the presumed bubbles can reach up to 1.8 inches or 4.6 cm in diameter. Those bubbles are believed to take shape at depths of approximately 330 to 660 feet or 100 to 200 meters. The bubbling events may be transient phenomena. That's why the Magic Island may have completely disappeared since the observation of July 10, 2013 from the Radar Mapper of the Cassini spacecraft. Daniel Cordier put forward that if future missions aim at deploying submarines to the seas or lakes of the Orange Moon, « possible instabilities of the liquid at the sea bottom have to be taken into account. » Today, nothing is certain regarding the nature of the Magic Island but the hypothesis for streams of bubbles is favored by numerous researchers. Is there a hot spring or a cryovolcano spewing nitrogen bubbles from time to time or periodically beneath the lake or sea ? The debate is not over regarding this captivating extraterrestrial mystery.
The image above unveils several radar views of the same portion of the area of the well-known lake or sea Ligeia Mare. The original radar images were obtained at a different time between 2007 and 2014 with the Radar Mapper of the Cassini spacecraft. The bright and irregular coastline can be clearly noticed in the three views. A new island seems to have emerged in the image of July 10, 2013 since the bright feature was absent in the radar image of April 26, 2007. The view of August 21, 2014 shows that the feature has extended, diluted or dissolved. Was it really an island ? Image Credit: NASA/JPL-Caltech/ASI/Cornell.
|The image in the upper part of the table represents an
artist's impression of the coastline of Ligeia Mare where the bright
feature of the Magic Island appeared in a radar view obtained from the
Cassini probe on July 10, 2013. The simulated view is based on the Shape
From Shading Technique. In the radar view, landscape features which
appear brighter than other landscape features will be interpreted as
higher in elevation. The artist's rendition is based on a radar view
acquired on April 26, 2007 from the Radar Mapper of the Cassini probe.
The bright feature of the Magic Island was absent in the radar view. The
radar mosaic in the lower part of the table reveals the same region of
Ligeia Mare in 2007, in 2013 and in 2014. The Magic Island clearly
appears in the radar view of 2013. A grey arrow was incorporated into
the original mosaic to indicate the orientation of the virtual camera
unveiling the artist's rendering. Bays or peninsulas can be clearly
noticed but the Magic Island appears absent on the horizon.
Credit for the Artist's Impression:
Marc Lafferre, 2017.
- To get further information on that news, go to : http://www.space.com/36501-saturn-moon-titan-magic-island-bubbles.html and https://www.nature.com/articles/s41550-017-0102.
March 28, 2017 : New Experiments Suggest That Titanian Sands Are Electrically Charged
Recent experiments performed by scientists at the Georgia Institute of Technology imply that sands on Saturn's largest moon Titan are « electrically charged ». The outcome of the study which is entitled « Electrification of Sand on Titan and its Influence on Sediment Transport » has just been released in the journal Nature Geoscience. The analysis was led by Josh Méndez Harper, a Georgia Tech geophysics and electrical engineering doctoral student. The paper also involved Josef Dufek, the Georgia Tech professor who co-led the research work, George McDonald, a graduate student in the School of Earth and Atmospheric Sciences and scientists from the Jet Propulsion Laboratory, University of Tennessee-Knoxville and Cornell University. The analysis work is partially supported by the National Science Foundation (EAR-1150794). Josh Méndez Harper benefited from a National Science Foundation graduate fellowship during the research work whereas George McDonald benefited from a National Defense Science and Engineering Graduate Fellowship.
Titan is a world covered with significant amounts of organics or hydrocarbons. Radar data obtained from the Radar Mapper of the Cassini probe have clearly shown that the low-albedo areas of Titan are dominated by Seif Dunes or linear and parallel dunes extending over long distances. As a result, researchers have been in a position to study the influence of prevailing winds upon the shape or the formation process of dunes on the Opaque Moon. A significant part of Titan's surface may be composed of tholins, a material dominated by organics. Josh Méndez Harper and his team advance that if the force of the wind is strong enough with a speed of about 15 miles per hour (approximately 9 kilometers per hour), the non-silicate granules present on the soil or the ground will tend to take off and will begin to hop in a motion process known as saltation. This process implies interactions and collisions between particles or grains which become frictionally charged. Therefore, they aggregate or clump together with a behavior different from that of sand dune grains on our planet. The Titanian grains or compounds become resistant to further motion.
In a way, the electrically-charged grains or particles engender well-known electrical processes which can take shape, for instance, when you rub a balloon against your hair. The grains of the giant moon will maintain that electrical charge for days or months at a time and stick to other hydrocarbon compounds, much like packing peanuts used in shipping boxes in our well-known world. Josef Dufek pointed out : « If you grabbed piles of grains and built a sand castle on Titan, it would perhaps stay together for weeks due to their electrostatic properties.» He added : « Any spacecraft that lands in regions of granular material on Titan is going to have a tough time staying clean. Think of putting a cat in a box of packing peanuts.» One can wonder what the Huygens probe looks like today, since its landing on January 14, 2005. Is it partially or completely buried like in quicksands on Earth ?
Infrared or near-infrared views of the globe of Titan, taken from the VIMS instrument of the Cassini spacecraft, reveal a remarkable contrast between relatively high-albedo areas and relatively low-albedo areas. Radar data obtained from the Radar Mapper of the Cassini orbiter have allowed us to determine that the relatively dark areas, generally found at low latitudes, are dominated by Seif Dunes. The orientation of the linear and parallel dunes implies that prevailing winds on this fascinating moon blow from east to west at the lower altitude or at the level of the surface. Surprisingly, the dunes of sand, likely dominated by hydrocarbons or organics and which can be almost 300 feet tall or about 100 meters high, seem to take shape from west to east. Josh Méndez Harper advanced : « These electrostatic forces increase frictional thresholds.» He added : « This makes the grains so sticky and cohesive that only heavy winds can move them. The prevailing winds aren't strong enough to shape the dunes.» That's not what we could have imagined or concluded at first sight !
In order to test the movement of Titanian sands and the environment of the Orange Moon at the level of the surface or close to the soil, the group of researchers led by Josh Méndez Harper constructed a small experiment in a modified pressure container in their Georgia Tech Laboratory. They introduced grains of naphthalene (C10H8) and biphenyl (C12H10) into a little cylinder. They used these compounds which are toxic and composed of carbon and hydrogen because they are thought to be found on the Hazy Moon. Then, the researchers rotated the tube for 20 minutes in a dry, pure nitrogen environment since it is supposed to simulate the atmosphere of the Opaque Moon which is mainly composed of nitrogen with a nitrogen concentration of about 98 percent of the atmospheric composition. After this process, they measured the electric properties of each grain or compound as it tumbled out of the container.
Would we see aggregation or clumping phenomena due to electrical interactions ? Josh Méndez Harper pointed out : « All of the particles charged well, and about 2 to 5 percent didn't come out of the tumbler.» He added : « They clung to the inside and stuck together. When we did the same experiment with sand and volcanic ash using Earth-like conditions, all of it came out. Nothing stuck.» On the Blue Planet, sand gathers electrical charge when it is displaced. However, the electrical charges appear smaller and dissipate in a relatively short time. That's why we need water to solidify the structure of sand when building a sand castle. On Titan, the electrical conditions may favor the resistance of landforms such as dunes or sedimentary structures over time. George McDonald argued : « These non-silicate, granular materials can hold their electrostatic charges for days, weeks or months at a time under low-gravity conditions.»
To a certain extent, Titan resembles the Early Earth with its hazy atmosphere dominated by molecular nitrogen and containing a significant concentration of methane. Since the start of the Cassini/Huygens mission in mid-2004, we have collected a significant amount of information or clues regarding the composition and the dynamics of Titan's atmosphere and landscape. We were surprised to see that the low-albedo areas found at low latitudes on Titan are devoid of any significant pools of liquid methane or liquid ethane. But as soon as the year 2005, we found the first stable extraterrestrial lake or sea in the high latitudes of the southern hemisphere of the giant moon. This lake or sea which looks like a foot or a kidney was named Ontario Lacus. Over the years, we've been in a position to identify, thanks to radar data in particular, a large number of lakes, seas and rivers in the high latitudes of the northern hemisphere of the Orange Moon. The north polar region or the high northern latitudes of Titan appear to be the most humid areas of Titan today. The astonishing dichotomy in the distribution of lakes and seas on Titan is a major subject of study.
Thanks to the observations performed from the Cassini orbiter during numerous flybys of Titan, we know, now, that the Opaque Moon unveils familiar landscape features or meteorological phenomena such as cloud systems, cyclones or cirrus-like clouds. There are evaporation, condensation and precipitation processes on Titan like on Earth but the meteorological cycle of Titan involves methane molecules instead of water molecules. In the harsh environment of Saturn's largest moon, water can't appear in its liquid form. Water will remain in its solid form on the surface or close to the surface. The lakes, seas or rivers of Titan are thought to be mainly composed of methane and ethane. They may also contain dissolved nitrogen which can generate bubbles on the surface like CO2 on the surface of a Champagne bottle.
There may be several types of lakes or seas of hydrocarbons on Titan. Some lakes or seas may be mainly composed of methane whereas other lakes may be dominated by ethane. Seasonal factors may play a key role in the dynamics of Titan's atmosphere and the composition of lakes and seas may evolve over time. Relatively complex organics or hydrocarbons can take shape in the upper atmosphere of Titan and fall to the surface to form tholins. Titan is covered with a remarkably complex atmosphere. The atmospheric pressure on the surface of Titan is even higher than that of the Earth at sea level since it evolves around 1,5 Bar compared to about 1 Bar on Earth at sea level. To a certain extent, standing on Titan would be similar, in terms of physics, to standing 15 feet (about 5 meters) underwater on the Blue Planet. Josef Dufek advanced : « Titan's extreme physical environment requires scientists to think differently about what we've learned of Earth's granular dynamics.» He concluded : « Landforms are influenced by forces that aren't intuitive to us because those forces aren't so important on Earth. Titan is a strange, electrostatically sticky world.» Electrons and electricity are everywhere in nature ! We undoubtedly have a lot to learn regarding the chemistry of organics on Titan which may bring new clues regarding the giant puzzle of organics on Earth.
The image above corresponds to a portion of a radar swath obtained with the Radar Mapper of the Cassini spacecraft on October 28, 2005 during the T8 Flyby. The original radar swath unveiled the region of central Adiri, the region of central Belet, the landing site of the Huygens probe as well as the region of Antillia Faculae. The view, here, reveals an area dominated by linear and parallel dunes extending over long distances. One can notice the influence of bright topographic features upon the orientation of dunes. Relatively strong winds tend to shape the dunes which can be deflected by hills or mountains. Image Credit: NASA/JPL/Cassini RADAR team.
- To get further information on that news, go to: http://www.news.gatech.edu/2017/03/27/electric-sands-titan.
March 17, 2017 : New Simulations Suggest that Titan's Lakes or Seas May Fizz With Nitrogen
A new study published online in the journal Icarus in February entitled « Laboratory measurements of nitrogen dissolution in Titan lake fluids » and proposed by a team led by Michael Malaska suggests that the lakes or seas of Titan may fizz with nitrogen. This hypothesis is based on experiments simulating the environment of Titan where most lakes, seas or rivers are found. The simulations involved the hydrocarbons methane and ethane as well as nitrogen. The researchers advance that there may be occasional events of spectacular ebullition within the lakes or seas revealing patches of bubbles.
The team of Michael Malaska who is from NASA's Jet Propulsion Laboratory in Pasadena, California simulated the harsh environmental conditions in the land of lakes and seas on Saturn's largest moon and mobilized key ingredients of the lakes or seas that is to say methane, ethane and nitrogen. The specialists observed that significant amounts of nitrogen can be dissolved within liquid methane that can form clouds, fall as rain and form lakes, seas or rivers on Titan. They managed to demonstrate that relatively small changes in temperature, air pressure or composition can engender dissociation of nitrogen from the liquid with bubbles. In other words, the solution of liquid methane or liquid ethane is likely to fizz and to produce bubbles of nitrogen. That's a process resembling the ebullition phenomenon when you open a bottle of carbonated soda.
The data obtained from the Cassini spacecraft reveal that the bodies of liquids on the Opaque Moon are mostly found at high latitudes or in the polar regions, the north polar region appearing to be the most humid area of Titan today. The composition of the lakes or seas can vary depending on the area. Some pools of liquid are mostly composed of methane whereas other bodies of surface liquid are mostly composed of ethane. Michael Malaska advanced : « Our experiments showed that when methane-rich liquids mix with ethane-rich ones - for example from a heavy rain, or when runoff from a methane river mixes into an ethane-rich lake – the nitrogen is less able to stay in solution.» As a result, one can observe numerous bubbles like in a champagne bottle.
Seasonal changes may strongly influence the behavior of nitrogen elements or molecules within the lakes or seas of methane or ethane. If the pools of methane warm slightly due to seasonal factors for instance, the nitrogen compounds present within the liquid may tend to dissociate themselves and to go up to the surface to form bubbles and become an atmospheric gas. Let's point out that the atmosphere is mostly composed of nitrogen like the atmosphere of the Earth. In fact, the hazy atmosphere of Titan rich in methane, in hydrocarbons or organics looks like the presumed atmosphere of the Early Earth. Engineers and scientists who may plan a new mission to Titan with a probe, a lander, a submarine or a drone to the methane or ethane lakes or seas must take into account, in the development of any craft, the fact that the lakes or seas on Titan can potentially be quite fizzy. Excess heat related to the working system of the probe may engender bubbles in the liquid around the craft, in particular at the level of the propellers which propel or orientate the probe. The probe may become hard to control or to steer.
The hypothesis regarding fields of bubbles at the surface or above the lakes or seas had been advanced recently to explain the mystery of the « Magic Islands » which represented bright, transient surface features whose shape had evolved, which had disappeared or reappeared between several radar observations of the same area within the lake or sea near the coast. Several hypotheses had been put forward including the presence of strong waves or evolving materials like icebergs. The radar images obtained from the Radar Mapper of the Cassini spacecraft allow researchers to study the topography, the landscape or the lakes, seas and rivers thanks to brightness variations. One can notice islands for instance within the famous lake or sea Ligeia Mare. But was the Magic Island really an island ? It disappeared so rapidly on the basis of several observations that it is hard to believe it ! In at least one case, we have observed a reappearance of the bright surface features related to the Magic Island phenomenon.
The new study proposed by Michael Malaska and his team brings details regarding basic physical or chemical mechanisms involving key ingredients of Titan's pools and atmosphere and demonstrates, on the basis of relevant or realistic experiments, that the hypothesis for nitrogen bubbles or fizzy lakes or seas must be seriously considered. Jason Hofgartner of JPL who is a co-author of the analysis and who serves as a co-investigator on Cassini's radar team pointed out : « Thanks to this work on nitrogen's solubility, we're now confident that bubbles could indeed form in the seas, and in fact may be more abundant than we'd expected.» It is interesting to analyze the interactions between hydrocarbons and nitrogen which is widespread in planetary atmospheres like the atmosphere of Venus, the Earth or Mars. Could there be a subsurface layer of liquid nitrogen for instance ?
Michael Malaska and his collaborators used liquid ethane in the simulation to simulate a type of sea or lake on Titan. They incorporated nitrogen into the solution which was mainly composed of ethane to see how it behaved. The scientists coaxed nitrogen out of the solution as the ethane molecules froze to the bottom of the tiny body of surface liquid. Solid ethane is denser than liquid ethane whereas solid water or water ice is less dense than liquid water. That's why water ice or icebergs float on liquid water on Earth. This configuration is not possible with solid ethane because it would sink within liquid ethane unless it is made of a lot of empty spaces or pockets inside it. As a result, one can expect that ethane ice would form on the bottom of the Titanian lakes if the physical conditions are met. During the process of crystallization of ethane into ice, the dissolved nitrogen gas will tend to go out and to go up to the surface where it will fizz out or form bubbles.
It's quite hard to imagine a harsh environment where water is as hard as rock with such a dynamics or activity. We have boiling water on Earth and there is probably boiling ethane or boiling methane in the lakes or seas of Titan. How often does it happen ? New questions regarding the lakes, seas and rivers of Titan take shape as the mission advances. Michael Malaska argued that the movement of nitrogen on the Orange Moon doesn't just evolve in one direction. Nitrogen must go into the methane molecules and the ethane molecules before it can be released into the atmosphere. Michael Malaska pointed out : « In effect, it's as though the lakes of Titan breathe nitrogen.» He added : « As they cool, they can absorb more of the gas, 'inhaling'. And as they warm, the liquid's capacity is reduced, so they 'exhale'.» A parallel can be drawn between this mechanism and the process of carbon dioxide absorption by the oceans of the Earth.
The final close flyby of the Hazy Moon by the Cassini spacecraft which will be the 127th targeted encounter with Titan is expected for April 22, 2017. This special flyby has been optimized to perform a remarkable observation campaign of the land of lakes and seas in the northern hemisphere of the Opaque Moon. The Radar Mapper will steer its radar beam toward the northern seas and lakes in order to collect new clues regarding the appearance and the dynamics of the pools of liquids. Will there be changes in the appearance of the coastline or in the albedo of the lakes or seas for instance ? The upcoming radar campaign has been well prepared by the radar team. Researchers should be in a position to analyze potential brightness changes within the lakes or seas. In other words, if features associated with the Magic Island phenomenon are spotted this time, planetologists may be able to determine whether the new bright patches correspond to bubbles, waves, floating materials, icebergs or suspended solids.
The final flyby of Titan performed by the Cassini spacecraft will allow the probe to change or to bend its course to start its final series of 22 plunges through the gap between the Gas Giant Saturn and its innermost rings. This process has been called Cassini's Grand Finale. The Cassini/Huygens spacecraft left our planet in 1997. Therefore, this is a 20-year mission that will end with a spectacular dive of the Cassini spacecraft into Saturn's atmosphere on September 15, 2017. The probe will have studied the dynamics, the nature or the composition of Titan's atmosphere and of Titan's lakes and seas for a long time but for less than a Titanian year which lasts almost 30 Terrestrial years. Now, we know the Summer season in the area of Ontario Lacus in the south polar region but unfortunately, we won't have the opportunity, this time, to perform an in-depth study of the Summer season in the land of lakes and seas of the northern hemisphere because it will only start in a few weeks and it will last around seven Terrestrial years. Will the lake levels diminish due to strong evaporation processes and will the cloud activity increase ? Titan has undoubtedly a lot to teach us.
The image above represents a mosaic view based on near-infrared images acquired during a distant flyby of Titan performed by the Cassini spacecraft on February 17, 2017. On can clearly notice the famous sea Kraken Mare as well as Ligeia Mare and Punga Mare. A bright cloud patch can be identified in the area of Punga Mare in particular. Cirrus-like clouds can also be noticed at mid-latitudes. Is there more evaporation than precipitation in the land of lakes and seas of the north polar region ? Image Credit: NASA/JPL-Caltech/Space Science Institute.
The mosaic view above reveals the area of Ligeia Mare in false color. The view on the right corresponds to Ligeia Mare whereas the four views on the left correspond to an area of Ligeia Mare where a portion of the land seems to have completely disappeared in a relatively short period. The five Synthetic Aperture Radar views obtained with the Radar Mapper of the Cassini spacecraft were obtained between 2007 and 2014. The view on the upper left was taken on April 26, 2007. The second view from top-left was acquired on July 10, 2013. The third view from top-left was captured on August 21, 2014 and the fourth view from top-left was taken on January 11, 2015. A bright patch is present in the second view from top-left but absent in the first view from top-left. In the third view from top-left, it seems to be disintegrating or dissolving and in the fourth view from top-left, it seems to have completely disappeared. What was it ? An exotic iceberg ? A field of bubbles ? Hot springs ? Relatively strong waves ? Image Credit: NASA/JPL-Caltech/ASI/Cornell.
The image above corresponds to an artist's impression of Ligeia Mare where nitrogen bubbles may erupt from the surface of the liquid, from time to time, depending on seasonal factors or meteorological conditions. A slight warming process is likely to engender the release of a significant amount of nitrogen gas from a lake or sea dominated by methane or ethane. If the environmental temperature drops, for instance, the concentration of dissolved nitrogen inside the lake or sea may increase. That's what recent experiments led by Michael Malaska imply. Image Credit: Marc Lafferre, 2017.
- To get further information on that news, go to: https://saturn.jpl.nasa.gov/news/3008/experiments-show-titan-lakes-may-fizz-with-nitrogen.
March 13, 2017 : A New Study Suggests That We May Find An Exotic Lifeform Or Biochemistry On Titan
The Cassini probe and the Huygens probe have gathered a remarkable amount of data regarding Titan since the beginning of the mission inside the Saturnian System in mid-2004 and have revealed an intriguing world unveiling processes which can appear quite familiar to us. The researchers had long suspected the presence of seas or oceans on the surface of Saturn's largest moon and now we can confirm this captivating hypothesis. Titan turns out to be a dynamic world with a varied landscape and a complex atmosphere. Titan is clearly a geologically active world with a limited amount of impact craters as opposed to most moons of the Gas Giant Saturn.
Very few moons in the Solar System have a significant atmosphere. One can mention Triton, the main moon of Neptune and the Smoggy Moon Titan. Ganymede, the largest moon of Jupiter and the largest moon in the Solar System which is a little bit bigger than Titan has no significant atmosphere for instance. That can appear surprising at first sight. We knew that the opaque atmosphere of the Orange Moon was mainly composed of molecular nitrogen with a significant fraction of methane. We now know that a complex organic chemistry can be generated in this exotic atmosphere where clouds or cyclones can be found, in particular at high latitudes.
The Huygens probe landed at a low latitude, in the Adiri/Shangri-La region where bright areas and dark areas can be identified. The aerial views unveiled dark fractures, canyons or drainage channels on bright hills. Researchers and the general public became aware that rainfall can occur in the area engendering rivers or brooks. The probe did not land on a sea or ocean but the images acquired from the landing spot revealed eroded stones or pebbles implying that the landing site may be a dried-up river or brook. In fact, the infrared or near-infrared images as well as the radar views obtained from the Cassini spacecraft have shown that most lakes and seas are found in the high latitudes or in the polar regions of the giant moon. Thre north polar region is clearly the most humid region of Titan. Why ? That's a major question scientists are trying to bring a convincing answer.
Like several moons or Dwarf Planets in the Solar System like Europa, Ganymede, Enceladus, Triton or Pluto, Titan may contain an internal ocean of liquid water which may be salty like the ocean on our planet. Therefore, several liquids may be found in large amounts on or inside Titan, methane, ethane and water beneath the icy crust. Titan has a meteorological cycle of methane comparable to the water cycle of our planet. There are seas, lakes, rivers, canyons, dune fields, mountains and erosional processes via winds, rainfall or snowfall like on Earth. The atmosphere of Titan may be quite similar to the atmosphere of the Early Earth. That's why we often say that Titan is a « prebiotic laboratory ».
Is there a lifeform or biochemistry on Titan or inside Titan ? The Cassini/Huygens mission has not allowed researchers to provide a clear answer to this question but it strengthens our will to deepen our study of Titan. Titan has a great potential to provide significant clues regarding the complex chemistry of carbon or organics. Sarah Hörst who is a planetary researcher with Johns Hopkins University in Baltimore pointed out in a paper entitled « Titan's Atmosphere and Climate » published in an upcoming edition of the Journal of Geophysical Research : « The combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that Titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. »
Can there be two or three lifeforms on and inside Titan since there may be two or three types of stable liquids ? The lakes, seas and rivers of the polar regions may be mainly dominated by a mixture of methane and ethane. As a result, we may find a lifeform or a biochemistry based on liquid methane or liquid ethane at the level of lakes, seas and rivers. The hypothetical ocean of liquid water may harbor a lifeform based on liquid water. Some researchers had advanced the hypothesis for a subsurface layer of liquids dominated by ammonia. Can we also envisage a lifeform based on ammonia ? That's a question we can't rule out. The large amount of organics present on the surface may progressively migrate downward toward the hypothetical subsurface ocean of water representing a significant nutrient source for the hypothetical lifeforms of the subsurface ocean. Thus, a methane cycle between the subsurface ocean, the ground and the atmosphere may occur.
Titan appears to be a soup of organics and hydrocarbons. The atmosphere engenders complex organics which appear in the haze or smog and can fall to the surface where they produce tholins, a kind of orange or red mud or sediment rich in organics. What type of organics can we find ? Are there amino acids on Titan since those molecules appear to be the building blocks of proteins and life on Earth ? The environmental temperature at the level of the surface on Titan is extremely low. That's why chemical reactions will be largely slower than the chemical reactions on Earth. However, Titan has all the ingredients of life as we know it that's to say carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. We are CHNOPS on Earth which means that we are mainly composed of the 6 elements mentioned here !
The hydrocarbons of Titan may be abiogenic as opposed to the hydrocarbons on Earth which are the outcome of ancient life. Methane and ethane which appear in the form of gas on Earth will appear in their liquid form on the surface of Titan because there is the right combination of environmental temperature and atmospheric pressure at the level of the surface. On the surface of the Earth, the environmental temperature is largely too high for methane or ethane to appear in their liquid form. There may be more hydrocarbons on Titan than on Earth. We'll have to sample the haze of Titan because it may resemble the prebiotic environment of the Early Earth as advanced in a 2015 NASA Astrobiology Strategy report.
Elizabeth Turtle who is a planetary scientist with the John Hopkins University Applied Physics Laboratory in Laurel, Maryland pointed out : « Titan gives us the opportunity to search for signatures of life in multiple types of systems - familiar water-based life, but also a biological system that may have developed with hydrocarbon as a solvent.» Britney Schmidt, another planetary scientist of Georgia Tech advanced that Saturn's largest moon provides many examples of captivating or intriguing organic chemistry analyses with alternative structures. She argued : « The Titan example is fantastic because you have a sedimentary process like a terrestrial planet, but it's ice involved.» She added : « It's organic in nature, but it is not necessarily biogenic.» Researchers want to have a better idea regarding the boundary between living molecules and non-living molecules.
Planetology needs more in situ exploration of planetary bodies in order to better understand the nature of their soil or atmosphere. If we could send long-lasting rovers to Titan like we did for Mars with Spirit, Opportunity or Curiosity, we would have a better view of its complex chemistry but we can't rely on solar panels at the level of Saturn or Titan. Moons like Triton or Europa are key targets for scientists but every mission to the Outer Solar System represents a significant investment and is complex to achieve. Researchers are now planning a new mission to Europa which may harbor a salty subsurface ocean of liquid water. The last pass of Titan for the Cassini spacecraft will occur in April. Thus, researchers will then have time to envisage a new mission to this fascinating moon. Scientists agree to say that the lakes or seas of Titan deserve a lander, a boat, a balloon or a drone.
The Astrobiology Strategy report pointed out : « The distribution of watery worlds in our solar system and beyond challenges our limited understanding of life's emergence on Earth and encourages us to think about the environmental conditions amenable to life.» The puzzle is still far from being complete. Astrobiologist Kevin Hand of NASA's Jet Propulsion Laboratory in Pasadena, California argued : « What we're trying to do with the exploration of Europa and the ocean worlds is nothing short of revolutionizing science, revolutionizing our understanding of whether or not biology works beyond Earth.» He added : « We know that physics, chemistry and geology all work beyond Earth.» He concluded : « But when it comes to that fourth fundamental science we have yet to make that leap.» Do Kraken Mare, Ligeia Mare or Punga Mare reveal exotic natural processes or an exotic biochemistry ? That's probably the biggest question regarding Titan. And the scenery must be really captivating !
The image above reveals a view of the disk of Saturn's largest moon obtained with the Wide-Angle Camera of the Cassini spacecraft on January 1, 2014. The camera incorporated a spectral filter sensitive to wavelengths of near-infrared light centered at 939 nanometers for this view. The atmosphere of Titan is completely opaque in the visible spectrum but in the infrared or near-infrared spectrum, landscape features can be discerned. One can notice, here, relatively dark patches representing lakes or seas in the high latitudes of the northern hemisphere. Image Credit: NASA/JPL-Caltech/Space Science Institute.
|The image in the upper part of this table reveals the
surface of a north polar lake on Titan. A delta found between mountains
can be seen on the horizon. The lake is probably mainly composed of
methane. The artistic image corresponds to a
simulated view of the area generated on the basis of the
Shape-From-Shading Technique. The image in the lower part of the table
corresponds to a radar view of the area represented in the simulated
photo. A grey arrow was incorporated into the original radar view,
collected with the Radar Mapper of the Cassini probe on October 9, 2006,
to indicate the orientation of the virtual camera producing the
simulated view of the landscape.
Credit for the Artist's Impression:
Marc Lafferre, 2017.
- To get further information on that news, go to: http://www.seeker.com/saturn-moon-titan-may-offer-glimpse-of-life-as-we-dont-know-it-2307762917.html.
January 14, 2017 : Flash-Back On the Remarkable Achievement of the Huygens Probe Which Landed at a Low Latitude On Titan About Twelve Years Ago
Prior to the Cassini-Huygens mission, nobody knew what the landscape of Titan looked like because the hazy or smoggy atmosphere of Saturn's largest moon is completely opaque from outer space. Researchers were fascinated and intrigued by this exotic and unique world which appears to be the second largest moon in the Solar System. Ganymede, the giant moon of Jupiter, is slightly bigger than Titan but paradoxically it is devoid of any significant atmosphere. Crazy or optimistic hypotheses regarding the nature of Titan's surface had been advanced such as the presence of a global ocean of methane or ethane.
Researchers knew that the environmental conditions on Titan allowed the potential presence of liquid methane, liquid ethane or liquid propane on the surface of the Orange Moon. At the relatively significant distance of Titan and Saturn from the Sun, the energy received from our own star is particularly low so that the environmental temperature on the Opaque Moon is aroud -179 degrees Celsius, -292 degrees Fahrenheit or 94 Kelvin. The atmospheric pressure at the level of the soil is around 1,5 Bars which is higher than that at sea level on Earth. Scientists knew that the atmosphere of Titan was dominated by molecular nitrogen and that methane represented the second most abundant compound in the hazy atmosphere. That's why the hypothesis of a global ocean of hydrocarbons was put forward by many scientists.
The Cassini-Huygens spacecraft reached the Saturnian System in mid-2004. The Cassini probe was equipped with several instruments such as the Radar Mapper and the Visual and Infrared Mapping Spectrometer or VIMS. Researchers were going to be able to collect data regarding the meteorology and the surface of Titan thanks to the Radar Mapper and thanks to the infrared and near-infrared eyes of the Cassini probe in particular. As soon as 2004, the Cassini probe collected the first data regarding the surface of the Opaque Moon revealing a contrast between high-albedo areas and low-albedo areas mostly found at low latitudes. Some scientists believed that those dark areas contrasting with bright areas represented seas or oceans of liquid methane or ethane even if some specialists argued that the low-albedo regions were not dark or uniform enough to be composed of liquids.
The Cassini probe of NASA dropped the lander known as Huygens on December 24, 2004 for a 20-day journey towards the surface of the Orange Moon. The Huygens module and its atmospheric shield could be compared with a flying saucer. The Huygens probe would have to withstand the harsh conditions of Titan's atmosphere. The designers or developers of the Huygens probe proposed by the European Space Agency had anticipated several configurations regarding the touchdown including a splash into a sea or ocean of hydrocarbons. That's why the Huygens module was able to float on an hypothetical sea, lake or river. The lifespan of the Huygens probe was particularly short due to its limited level of energy. The Huygens probe couldn't count on the solar energy which is too weak at this distance for conventional solar panels. The module had to rely on nuclear energy which would fuel the living probe for a few hours once on the surface of the giant moon.
The Huygens module performed a spectacular plunge into the Titanian atmosphere acquiring key data regarding the atmosphere and the landscape. A multitude of panoramic views were obtained from the parachuted probe and transmitted to the Cassini orbiter which had to be in the right place to collect the data. The Cassini spacecraft would rapidly go down below the horizon of the Huygens probe preventing new data from coming. During the atmospheric descent, the probe managed to obtain key data regarding the environmental temperature, the density, the atmospheric pressure, wind speed, the nature of the complex organics or the nature of the haze or the dense atmosphere. From the altitude of about 45 miles or 70 kilometers, the sky became clearer and the landscape could be discerned. The probe took remarkable images of the landscape revealing a radical contrast between a dark or brownish plain resembling a sea and bright hills resembling a glacier or banquise. Researchers and the general public were fascinated by what they saw. Dark sinuous channels in the bright areas or in the hills were clearly discerned in the views. Those channels are likely drainage channels or dried-up rivers. The aerial views led some persons or scientific journalists to advance that the dark plain corresponded to a methane sea.
During the historical atmospheric descent, hundreds of images were taken with the Descent Imager/Spectral Radiometer or DISR allowing the creation of a video of the descent. The area where the Huygens probe landed probably undergoes seasonal rainfall. That's what the aerial images suggest. Methane or ethane rain can produce strong erosional processes sculpting the landscape in the same way as on Earth and can engender canyons or steep ravines. The dark channels may also correspond to fractures even if the hypothesis for drainage channels at low latitudes is favored. After the touchdown, the Huygens probe survived and collected captivating views of the soil and the horizon. Eroded stones or pebbles could be clearly discerned near the probe implying that the probe may have landed onto an ancient river.
The Cassini probe which has been collecting key data regarding the atmosphere of Titan and its landscape is still operating today but its mission is expected to come to an end on September 15, 2017 with a big plunge into Saturn's atmosphere. The Cassini team members and NASA leaders have performed an extraordinary work over the years since the big start of the Cassini-Huygens mission in the Saturnian System in 2004. Here are some comments. Linda Spilker who is Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California advanced : « The Huygens descent and landing represented a major breakthrough in our exploration of Titan as well as the first soft landing on an outer-planet moon. It completely changed our understanding of this haze-covered ocean world.»
Carolyn Porco who is Cassini imaging team lead at Space Science Institute in Boulder, Colorado pointed out : « The Huygens images were everything our images from orbit were not. Instead of hazy, sinuous features that we could only guess were streams and drainage channels, here was incontrovertible evidence that at some point in Titan's history – and perhaps even now – there were flowing liquid hydrocarbons on the surface. Huygens' images became a Rosetta stone for helping us interpret our subsequent findings on Titan. » Since the beginning of the Cassini-Huygens mission, radar data obtained from the Cassini orbiter have clearly shown that the dark areas or low-albedo areas in the infrared or near-infrared spectrum found at low latitudes are dominated by Seif dunes or parallel and linear dunes extending over long distances and shaped by prevailing winds. As a result, one can advance the hypothesis that the low-albedo areas located at low latitudes may correspond to ancient seas.
Alex Hayes who is a Cassini scientist at Cornell University, Ithaca, New York argued : « Cassini and Huygens have shown us that Titan is an amazing world with a landscape that mimics Earth in many ways. During its descent, the Huygens probe captured views that demonstrated an entirely new dimension to that comparison and highlights that there is so much more we have yet to discover. For me, Huygens has emphasized why it is so important that we continue to explore Titan. » Researchers became aware in particular that there may be seasonal phenomena in the area such as seasonal rainfall or monsoon events. Eroded stones or pebbles identified on the surface near the probe were the proof that a stream of liquid hydrocarbons, methane, ethane or propane must have taken shape relatively recently where the probe landed.
Jim Green who is director of planetary science at NASA Headquarters in Washington advanced : « Twelve years ago, a small probe touched down on an orangish, alien world in the outer solar system, marking humankind's most distant landing to date. Studying Titan helps us tease out the potential of habitability of this tiny world and better understand the chemistry of the early Earth. » Thanks to the Radar Mapper, the infrared and near-infrared eye of the Cassini spacecraft, scientists have been in a position to obtain a relatively detailed map of Titan's surface and significant clues regarding the meteorology or the methane cycle on Titan. We know, now, that lakes, seas and rivers are found at high latitudes or in the polar regions of Titan. If we had known as soon as the start of the Saturnian journey that the pools of liquids were mostly concentrated in the high latitudes of the northern hemisphere, we would probably have sent the Huygens probe to seas or lakes like Kraken Mare, Ligeia Mare or Punga Mare. Are there huge waves as some researchers had predicted long ago ? Is there a complex organic chemistry within the pools of surface liquids dominated by hydrocarbons ? That's a major question we are eager to answer. Let's hope we'll have the answer very soon !
The image above corresponds to a panoramic view of the area where the Huygens probe landed on January 14, 2005. During its atmospheric descent, the Descent Imager/Spectral Radiometer acquired a multitude of images of its environment. This image represents a flattened (Mercator) projection of a view obtained at an altitude of 10 kilometers or 6 miles. One can notice the remarkable contrast between the dark, brownish plain and bright hills. Image Credit: ESA/NASA/JPL/University of Arizona.
The artist's impression above reveals the surface of Titan in a low-albedo area at a low latitude on Saturn's largest moon Titan. Radar images have clearly shown that the regions which appear dark and mark a clear contrast with bright areas at a low latitude are dominated by Seif dunes or linear and parallel dunes extending over long distances, influenced by prevailing winds. Winds and rainfall of methane or ethane can engender erosional processes like well-known meteorological processes occurring on Earth. Image Credit: Marc Lafferre, 2017.
- To get further information on that news, go to : https://saturn.jpl.nasa.gov/news/2987/huygens-ground-truth-from-an-alien-moon.