Titan News 2017

 

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: NASA/JPL-Caltech/ASI.
 

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.
Credit for the Radar Portion: NASA/JPL-Caltech/ASI.
Credit for the Incorporation of the Arrow into the Original Radar View: 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. 

Image Credit for the radar view of Vid Flumina: NASA/JPL-Caltech/ASI.
Image Credit for the view of the Nile River: Google Earth.
Image Credit for the view of the sinuous land on Mars: Google Earth.

- 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.
Credit for the Original Radar View: NASA/JPL-Caltech/ASI/Cornell.
Credit for the Incorporation of the Arrow into the Original Radar View: 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.
Credit for the Original Radar View: NASA/JPL/Cassini Radar Team.
Credit for the Incorporation of the Arrow into the Original Radar View: 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.

  

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