Titan News 2017
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 ancien 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 plane tectonics in the recent geological past.
The outcome of the study, 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 evolved. » 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 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 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.