A new study has revealed that Titan's methane lakes could be calm enough for future missions to land there. Credit: bisbos.com
Ever since the Cassini orbiter and the Huygens lander provided us with the first detailed glimpse of Saturn’s moon Titan, scientists have been eager to mount new missions to this mysterious moon. Between its hydrocarbon lakes, its surface dunes, its incredibly dense atmosphere, and the possibility of it having an interior ocean, there is no shortage of things that are worthy of research.
The only question is, what form would this mission take (i.e. aerial drone, submarine, balloon, lander) and where should it set down? According to a new study led by the University of Texas at Austin, Titan’s methane lakes are very calm and do not appear to experience high waves. As such, these seas may be the ideal place for future missions to set down on the moon.
Titan’s three largest lakes and their surrounding areas as seen by the Cassini RADAR instrument. The researchers used the instrument to study waves on the lake surfaces. Credit: Cyril Grima/ The University of Texas at Austin
As Grima explained in a University of Texas press release, this research also shed light on the meteorological activity on Titan:
“There’s a lot of interest in one day sending probes to the lakes, and when that’s done, you want to have a safe landing, and you don’t want a lot of wind. Our study shows that because the waves aren’t very high, the winds are likely low.”
Towards this end, Grima and his colleagues examined radar data obtained by the Cassini mission during Titan’s early summer season. This consisted of measurements of Titan’s northern lakes, which included Ontario Lacus, Ligeia Mare, Punga Mare, and Kraken Mare. The largest of the three, Kraken Mars, is estimated to be larger than the Caspian Sea – i.e. 4,000,000 km² (1,544,409 mi²) vs 3,626,000 km2 (1,400,000 mi²).
With the help of the Cassini RADAR Team and researchers from Cornell University, the Johns Hopkins University Applied Physics Laboratory (JHUAPL), NASA’s Jet Propulsion Laboratory (JPL) and elsewhere, the team applied a technique known as radar statistical reconnaissance. Developed by Grima, this technique relies on radar data to measure the roughness of surfaces in minute detail.
This technique has also been used to measure snow density and the surface roughness of ice in Antarctica and the Arctic. Similarly, NASA has used the technique for the sake of selecting a landing site on Mars for their Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (Insight) lander, which is scheduled to launch next year.
The left image shows a mosaic of images of Titan taken by the Cassini spacecraft in near infrared light. Titan’s polar seas are visible as sunlight glints off of them. The right image is a radar image of Kraken Mare. Credit: NASA Jet Propulsion Laboratory.
From this, Grima and his colleagues determined that waves on these lakes are quite small, reaching only 1 cm in height and 20 cm in length. These findings indicate that these lakes would be a serene enough environment that future probes could make soft landings on them and then begin the task of exploring the surface of the moon. As with all bodies, waves on Titan could be wind-driven, triggered by tidal flows, or the result of rain or debris.
As a result, these results are calling into question what scientists think about seasonal change on Titan. In the past, it was believed that summer on Titan was the beginning of moon’s windy season. But if this were the case, the results would have indicated higher waves (the result of higher winds). As Alex Hayes, an assistant professor of astronomy at Cornell University and a co-author on the study, explained:
“Cyril’s work is an independent measure of sea roughness and helps to constrain the size and nature of any wind waves. From the results, it looks like we are right near the threshold for wave generation, where patches of the sea are smooth and patches are rough.”
These results are also exciting for scientists who are hoping to plot future missions to Titan, especially by those who are hoping to see a robotic submarine sent to Titan’s to investigate its lakes for possible signs of life. Other mission concepts involve exploring Titan’s interior ocean, its surface, and its atmosphere for the sake of learning more about the moon’s environment, its organic-rich environment and probiotic chemistry.
And who knows? Maybe, just maybe, these missions will find that life in our Solar System is more exotic than we give it credit before, going beyond the carbon-based life that we are familiar with to include the methanogenic.
A proposed eight-bladed drone (aka. "dragonfly") could be ideally suited for exploring Saturn's moon Titan in the coming decades. Credit: APL/Michael Carroll
With its dense and hydrocarbon-rich atmosphere, Titan has been a subject of interest for many decades. And with the success of the Cassini-Huygens mission, which began exploring Saturn and its system of moons back in 2004, there are many proposals on the table for follow-up missions that would explore the surface of Titan and its methane seas in greater depth.
The challenges that this presents have led to some rather novel ideas, ranging from balloons and landers to floating drones and submarines. But it is the proposal for a “Dragonfly” drone by researchers at NASA’s JHUAPL that seems particularly adventurous. This eight-bladed drone would be capable of vertical-takeoff and landing (VTOL), enabling it to explore both the atmosphere and the surface of Titan in the coming decades.
ASA’s Cassini spacecraft looks toward the night side of Saturn’s largest moon and sees sunlight scattering through the periphery of Titan’s atmosphere and forming a ring of color. Credit: NASA/JPL-Caltech/Space Science Institute
Such a mission, as Turtle explained to Universe Today via email, is both timely and necessary. Not only would it build on many recent developments in robotic explorers (such as the Curiosity rover and the Cassini orbiter); but on Titan, there is simply no shortage of opportunities for scientific research. As she put it:
“Titan’s an ocean world with a unique twist, which is the rich and complex organic chemistry occurring in its atmosphere and on its surface. This combination makes Titan a particularly good target for studying planetary habitability. One of the big questions about the development of life is how chemical interactions led to biological processes. Titan’s been doing experiments in prebiotic chemistry for millions of years – timescales that are impossible to reproduce in the lab – and the results of these experiments are there to be collected.”
Their proposal is based in part on previous Decadal Surveys, such as the Campaign Strategy Working Group (CSWG) on Prebiotic Chemistry in the Outer Solar System. This survey emphasized that a mobile aerial vehicle (i.e an airship or a balloon) would well-suited to exploring Titan. Not only is Titan the only known body other than Earth that has a dense, nitrogen-rich atmosphere – four times as dense as Earth’s – but it’s gravity is also about 1/7th that of Earth’s.
However, balloons and airships would be unable to study Titan’s methane lakes, which are one of the most exciting draws as far as research into prebiotic chemistry goes. What’s more, an aerial vehicle would not be able to conduct in-situ chemical analysis of the surface, much like what the Mars Exploration Rovers (Spirit, Opportunity and Curiosity) have been doing on Mars.
Artist’s concept of a Titan Aerial Daughter quadcopter and its “Mothership” balloon. Credit: NASA/STMD
As such, Turtle and her colleagues began looking for a proposal that represented the best of both worlds – i.e. an aerial platform and a lander. This was the genesis of the Dragonfly concept.
“Several different methods have been considered for in-situ aerial exploration of Titan (helicopters, different types of balloons, airplanes),” said Turtle. “Dragonfly takes advantage of the recent developments in multi-rotor aircraft to provide aerial mobility for a lander with a sophisticated payload. Because Dragonfly would be able to travel long distances – a few tens of kilometers at a time, and up to a few hundred kilometers over the course of the mission – it would be possible to make measurements at multiple sites with very different geologic histories.”
The mission is also in keeping with concepts that Turtle and her colleagues – which includes Ralph Lorenz (also from JHUAPL), Melissa Trainer of the Goddard Space Flight Center, and Jason Barnes of University of Idaho – have been exploring for years. In the past, they proposed a mission concept that would combine a Montgolfière-style balloon with a Pathfinder-like lander. Whereas the balloon would explore Titan from a low altitude, the lander would explore the surface up close.
By the 48th Lunar and Planetary Science Conference, they had officially unveiled their “Dragonfly” concept, which called for a qaudcopter to conduct both aerial and surface studies. This four-rotor vehicle, it was argued, would be able to take advantage of Titan’s thick atmosphere and low gravity to obtain samples and determine surface compositions in multiple geological settings.
Artist’s concept of the dragonfly being deployed to Titan and commencing its exploration mission. Credit: APL/Michael Carroll
In its latest iteration, the Dragonfly incorporates eight rotors (two positioned at each of its four corners) to achieve and maintain flight. Much like the Curiosity and upcoming Mars 2020 rovers, the Dragonfly would be powered by a Multimission Radioisotope Thermoelectric Generator (MMRTG). This system uses the heat generated by decaying plutonium-238 to generate electricity, and can keep a robotic mission going for years.
This design, says Turtle, would offer scientists the ideal in-situ platform for studying Titan’s environment:
“Dragonfly would be able to measure compositional details of different surface materials, which would show how far organic chemistry has progressed in different environments. These measurements could also reveal chemical signatures of water-based life (like that on Earth) or even hydrocarbon-based life, if either were present on Titan. Dragonfly would also study Titan’s atmosphere, surface, and sub-surface to understand current geologic activity, how materials are transported, and the possibility of exchange of organic material between the surface and the interior water ocean.”
This concept incorporates a lot of recent advances in technology, which include modern control electronics and advances in commercial unmanned aerial vehicle (UAV) designs. On top of that, the Dragonfly would do away with chemically-powered retrorockets and could power-up between flights, giving it a potentially much longer lifespan.
Artist’s impression of the view from the surface of Titan, looking over one of its methane seas. Credit: NASA
“And now is the perfect time,” says Turtle, “because we can build on what we’ve learned from the Cassini-Huygens mission to take the next steps in Titan exploration.”
Currently, NASA’s Jet Propulsion Laboratory is developing a similar concept. Known as the Mars Helicopter “Scout”, for use on Mars, this aerial drone is expected to be launched aboard the Mars 2020 mission. In this case, the design calls for two coaxial counter-rotating rotors, which would provide the best thrust-to-weight ratio in Mars’ thin atmosphere.
This sort of VTOL platform could become the mainstay in the coming decades, wherever long-term missions that involve bodies that have atmospheres are called for. Between Mars and Titan, such aerial drones could hop from one area to the next, obtaining samples for in-situ analysis and combining surface studies with atmospheric readings at various altitudes to get a more complete picture of the planet.
NASA’s Cassini spacecraft captured the view on April 13, 2017 at 12:41 a.m. CDT. The probe was 870 million miles (1.4 billion km) away from Earth when the image was taken. The part of Earth facing toward Cassini at the time was the southern Atlantic Ocean. Look closely to the left of Earth; that pinprick of light is the Moon. Credit: NASA/JPL Caltech
Look at us. Packed into a gleaming dot. The entire planet nothing more than a point of light between the icy rings of Saturn. The rings visible here are the A ring (top), followed by the Keeler and Encke gaps, and finally the F ring at bottom. During this observation, Cassini was looking toward the backlit rings with the sun blocked by the disk of Saturn.
Cassini first photographed Earth from Saturn in July 2013. Credit: NASA/JPL-Caltech
Seen from Saturn, Earth and the other inner solar system planets always appear close to the sun much like Venus and Mercury do from Earth. All orbit interior to Saturn; even at maximum elongation, they never get far from the Sun. Early this month, as viewed from Saturn, Earth was near maximum elongation east of the sun, thus an “evening star,” making it an ideal time to take a picture.
In this cropped view of the April 13 image, you can better see the Moon, located a short distance to the left of the Earth. Credit: NASA/JPL-Caltech
Opportunities to capture Earth from Saturn have been rare in the 13 years Cassini has spent orbiting the ringed planet. The only other photo I’m aware of was snapped on July 19, 2013. Each is a precious document with a clear message: we are all tiny, please let’s be kind to one another.
This graphic shows Cassini’s flight path during the final two phases of its mission. The 20 Ring-Grazing Orbits are in gray (completed) and the 22 Grand Finale Orbits are in blue. The final partial orbit is colored orange. The first of the Grand Finale orbits begins on April 22 at 10:46 p.m. CDT. Credit: NASA/JPL-Caltech/Space Science Institute
We’ll soon miss the steady stream of artistic images of Saturn, its rings and moons by the Cassini team. The probe will make its final close flyby of the planet’s largest moon, fog-enshrouded Titan, at 1:08 a.m. April 22, at a distance of just 608 miles (979 km). That night at 10:46 p.m. CDT, Cassini will enter the first of its Grand Finale orbits, a series of 22 weekly dives between the planet and the rings. The first ring plane crossing is slated for midnight CDT April 25-26.
Cassini at Saturn and the Grand Finale
The coming week will be a busy one for Cassini. On each orbit, the probe will draw closer and closer to the butterscotch ball of Saturn until it finally tears across the cloud tops and burns up as a spectacular fireball on September 15. Scientists would rather see the craft burn up in Saturn’s atmosphere instead crash into a moon and possibly contaminate it.
Cassini will become a brilliant fireball streaking over Saturn’s cloud tops on the last day of its operation on September 15. Credit: NASA/JPL-Caltech
After nearly 20 years in space, seven of them spent traveling to the ringed planet, Cassini feels like family. It won’t be easy to say goodbye, but thanks to the probe, Saturn’s family album is bursting with remarkable images that will forever remind us the tenacity of this amazing machine and the vision and work of those who kept it operating for so many years.
The appearing and disappearing feature observed in Titan's Lakes was dubbed "Magic Island". Image: NASA/JPL-Caltech/ASI/Cornell
Saturn’s largest Moon, Titan, is the only other world in our Solar System that has stable liquid on its surface. That alone, and the fact that the liquid is composed of methane, ethane, and nitrogen, makes it an object of fascination. The bright spot features that Cassini observed in the methane seas that dot the polar regions only deepen the fascination.
A new paper published in Nature Astronomy digs deeper into a phenomenon in Titan’s seas that has been puzzling scientists. In 2013, Cassini noticed a feature that wasn’t there on previous fly-bys of the same region. In subsequent images, the feature had disappeared again. What could it be?
One explanation is that the feature could be a disappearing island, rising and falling in the liquid. This idea took hold, but was only an initial guess. Adding to the mystery was the doubling in size of these potential islands. Others speculated that they could be waves, the first waves observed anywhere other than on Earth. Binding all of these together was the idea that the appearance and disappearance could be caused by seasonal changes on the moon.
Titan’s dense, hydrocarbon rich atmosphere remains a focal point of scientific research. Credit: NASA
Now, scientists at NASA’s Jet Propulsion Laboratory (JPL) think they know what’s behind these so-called ‘disappearing islands,’ and it seems like they are related to seasonal changes.
The study was led by Michael Malaska of JPL. The researchers simulated the frigid conditions on Titan, where the temperature is -179.2 Celsius. At that temperature, some interesting things happen to the nitrogen in Titan’s atmosphere.
On Titan, it rains. But the rain is composed of extremely cold methane. As that methane falls to the surface, it absorbs significant amounts of nitrogen from the atmosphere. The rain hits Titan’s surface and collects in the lakes on the moon’s polar regions.
The researchers manipulated the conditions in their experiments to mirror the changes that occur on Titan. They changed the temperature, the pressure, and the methane/ethane composition. As they did so, they found that nitrogen bubbled out of solution.
“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,” said Michael Malaska of JPL. This release of nitrogen is called exsolution. It can occur when the seasons change on Titan, and the seas of methane and ethane experience a slight warming.
“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,” said Jason Hofgartner of JPL, a co-author of the study who also works on Cassini’s radar team. These nitrogen bubbles would be very reflective, which explains why Cassini was able to see them.
The first-ever images of the surface of a new moon or planet are always exciting. The Huygens probe was launched from Cassini to the surface of Titan, but was not able investigate the lakes and seas on the surface. Image Credit: ESA/NASA/JPL/University of Arizona
The seas on Titan may be what’s called a prebiotic environment, where chemical conditions are hospitable to the appearance of life. Some think that the seas may already be home to life, though there’s no evidence of this, and Cassini wasn’t equipped to investigate that premise. Some experiments have shown that an atmosphere like Titan’s could generate complex molecules, and even the building blocks of life.
NASA and others have talked about different ways to explore Titan, including balloons, a drone, splashdown landers, and even a submarine. The submarine idea even received a NASA grant in 2015, to develop the idea further.
So, mystery solved, probably. Titan’s bright spots are neither islands nor waves, but bubbles.
Cassini’s mission will end soon, and it’ll be quite some time before Titan can be investigated further. The question of whether Titan’s seas are hospitable to the formation of life, or whether there may already be life there, will have to wait. What role the nitrogen bubbles play in Titan’s life question will also have to wait.
The Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR) concept for an aerial explorer for Titan. Credit: Mike Malaska
Last week, from Monday Feb. 27th to Wednesday March 1st, NASA hosted the “Planetary Science Vision 2050 Workshop” at their headquarters in Washington, DC. During the course of the many presentations, speeches and addresses that made up the workshop, NASA and its affiliates shared their many proposals for the future of Solar System exploration.
A very popular theme during the workshop was the exploration of Titan. In addition to being the only other body in the Solar System with a nitrogen-rich atmosphere and visible liquid on its surface, it also has an environment rich in organic chemistry. For this reason, a team led by Michael Pauken (from NASA’s Jet Propulsion Laboratory) held a presentation detailing the many ways it can be explored using aerial vehicles.
The presentation, which was titled “Science at a Variety of Scientific Regions at Titan using Aerial Platforms“, was also chaired by members of the aerospace industry – such as AeroVironment and Global Aerospace from Monrovia, California, and Thin Red Line Aerospace from Chilliwack, BC. Together, they reviewed the various aerial platform concepts that have been proposed for Titan since 2004.
Artist depiction of the ESA’s Huygens lander setting down on Titan, which took place on January 14th. Credit: ESA
While the concept of exploring Titan with aerial drones and balloons dates back to the 1970s and 80s, 2004 was especially important since it was at this time that the Huygens lander conducted the first exploration of the moon’s surface. Since that time, many interesting and feasible proposals for aerial platforms have been made. As Dr. Pauken told Universe Today via email:
“The Cassini-Huygens mission revealed a lot about Titan we didn’t know before and that has also raised a lot more questions. It helped us determine that imaging the surface is possible below 40-km altitude so it’s exciting to know we could take aerial photos of Titan and send them back home.”
These concepts can be divided into two categories, which are Lighter-Than-Air (LTA) craft and Heavier-Than-Air (HTA) craft. And as Pauken explained, these are both well-suited when it comes to exploring a moon like Titan, which has an atmosphere that is actually denser than Earth’s – 146.7 kPa at the surface compared to 101 kPa at sea level on Earth – but only 0.14 times the gravity (similar to the Moon).
“The density of Titan’s atmosphere is higher than Earth’s so it is excellent for flying lighter-than-air vehicles like a balloon,” he said. “Titan’s low gravity is a benefit for heavier-than-air vehicles like helicopters or airplanes since they will ‘weigh’ less than they would on Earth.”
Titan’s atmosphere makes Saturn’s largest moon look like a fuzzy orange ball in this natural-color view from the Cassini spacecraft. Cassini captured this image in 2012. Credit: NASA/JPL-Caltech/Space Science Institute
“The Lighter-than-air LTA concepts are buoyant and don’t need any energy to stay aloft, so more energy can be directed towards science instruments and communications. The Heavier-than-air concepts have to consume power to stay in the air which takes away from science and telecom. But HTA can be directed to targets more quickly and accurately the LTA vehicles which mostly drift with the winds.”
TSSM Montgolfiere Balloon:
Plans for using a Montgolfiere balloon to explore Titan go back to 2008, when NASA and the ESA jointly developed the Titan Saturn System Mission (TSSM) concept. A Flagship Mission concept, the TSSM would consist of three elements including a NASA orbiter and two ESA-designed in-situ elements – a lander to explore Titan’s lakes and a Montgolfiere balloon to explore its atmosphere.
The orbiter would rely on a Radioisotopic Power System (RPS) and Solar Electric Propulsion (SEP) to reach the Saturn system. And on its way to Titan, it would be responsible for examining Saturn’s magnetosphere, flying through the plumes of Enceladus to analyze it for biological markers, and taking images of Enceladus’ “Tiger Stripes” in the southern polar region.
Artist’s concept of a Mongolfiere balloon and a deployable lander at Titan. Credit: NASA
Once the orbiter had achieved orbital insertion with Saturn, it would release the Montgolfiere during its first Titan flyby. Attitude control for the balloon would be provided by heating the ambient gas with RPS waste heat. The prime mission would last a total of about 4 years, comprised of a two-year Saturn tour, a 2-month Titan aero-sampling phase, and a 20-month Titan orbiting phase.
Of the benefits to this concept, the most obvious is the fact that a Montgolfiere vehicle powered by RPS could operate within Titan’s atmosphere for many years and would be able to change altitude with only minimal energy use. At the time, the TSSM concept was in competition with mission proposals for the moons of Europa and Ganymede.
In February of 2009, both the TSSM and the the Europa Jupiter System Mission (EJSM) concept were chosen to move forward with development, but the EJSM was given first priority. This mission was renamed the Europa Clipper, and is slated for launch in 2020 (and arriving at Europa by 2026).
Titan Helium Balloon:
Subsequent research on Montgolfiere balloons revealed that years of service and minimal energy expenditure could also be achieved in a much more compact balloon design. By combining an enveloped-design with helium, such a platform could operate in the skies of Titan for four times as long as balloons here on Earth, thanks to a much slower rate of diffusion.
Artist’s concept of the Mechanical Compression Altitude Control (MCAC) balloon, which is comprised of a number of segments that are compressed by shortening a tether that runs down the axis of the balloon. Credit: Thin Red Line Aerospace.
Altitude control would also be possible with very modest amounts of energy, which could be provided either through pump or mechanical compression. Thus, with an RPS providing power, the platform could be expected to last longer that comparable balloon designs. This envelope-helium balloon could also be paired with a glider to create a lighter-than-air vehicle capable of lateral motion as well.
Examples of the this include the Titan Winged Aerobot (TWA, shown below), which was investigated as part of NASA’s Phase One 2016 Small-Business Innovation Research (SBIR) program. Developed by the Global Aerospace Corporation, in collaboration with Northrop Grumman, the TWA is a hybrid entry vehicle, balloon, and maneuverable glider with 3-D directional control that could satisfy many science objectives.
Like the Mongtolfiere concept, it would rely on minimal power provided by a single RPS. Its unique buoyancy system would also allow it to descend and ascend without the need for propulsion systems or control surfaces. One drawback is the fact that it cannot land on the moon’s surface to conduct research and then take off again. However, the design does allow for low-altitude flight, which would allow for the delivery of probes to the surface.
Other concepts that have been developed in recent years include heavier-than-air aircraft, which center around the development of fixed-wing vehicles and rotorcraft.
Concept for a Titan Winged Aerobot, a hybrid balloon glider that does not require significant power either to stay aloft or to achieve lateral motion. Credit: Global Aerospace Corp/Northrup Grumman
Fixed Wing Vehicles:
Concepts for fixed-wing aircraft have also been proposed in the past for a mission to Titan. A notable example of this is the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR), an unmanned aerial vehicle (UAV) that was proposed by Jason Barnes and Lawrence Lemke in 2011 (of the University of Idaho and Central Michigan University, respectively).
Relying on an RPS that would use the waste heat of decaying Plutonium 238 to power a small rear-mounted turbine, this low-power craft would take advantage of Titan’s dense atmosphere and low gravity to conduct sustained flight. A novel “climb-then-glide” strategy, where the engine would shut down during glide periods, would also allow for power to be stored for optimal use during telecommunication sessions.
This addresses a major drawback of fixed-wing vehicles, which is the need to subdivide power between the needs of maintaining flight and conducting scientific research. However, the AVIATR is limited in one respect, in that it cannot descend to the surface to conduct science experiments or collect samples.
Rotorcraft:
Last, but not least, is the concept for a rotorcraft. In this case, the aerial platform would be a quadcopter, which would be well-suited to Titan’s atmosphere, would allow for easy ascent and descent, and for studies to be conducted on the surface. It would also take advantage of developments made in commercial UAVs and drones in recent years.
Artist’s concept of the Titan Aerial Daughtercraft (TAD) flying above one of Titan’s methane lake. Credit: NASA
This mission concept would consist of two components. On the one hand, there’s the rotorcraft – known as a Titan Aerial Daughtercraft (TAD) – which would rely on a rechargeable battery system to power itself while conducting short-duration flights (about an hour at a time). The second component is the “Mothercraft”, which would take the form of a lander or balloon, which the TAD would return to between flights to recharge from an onboard RPS.
Currently, NASA’s Jet Propulsion Laboratory is developing a similar concept, known as the Mars Helicopter “Scout”, for use on Mars – which is expected to be launched aboard the Mars 2020 mission. In this case, the design calls for two coaxial counter-rotating rotors, which would provide the best thrust-to-weight ratio in Mars’ thin atmosphere.
Another rotorcraft concept is being pursued by Elizabeth Turtle and colleagues from John Hopkins APL and the University of Idaho (including James Barnes). With support from NASA and members of Goddard Space Flight Center, Pennsylvania State University, and Honeybee Robotics, they have proposed a concept known as the “Dragonfly“.
Their aerial vehicle would rely on four-rotors to take advantage of Titan’s thick atmosphere and low gravity. Its design would also allow it to easily obtain samples and determine the composition of the surface in multiple geological settings. These findings will be presented at the upcoming 48th Lunar and Planetary Science Conference – which will be taking place from March 20th to 24th in The Woodlands, Texas.
Artist’s concept of the Titan Aerial Daughter quadcopter and its “Mothercraft” balloon. Credit: NASA/STMD
While the exploration of Titan is likely to take a back seat to the exploration of Europa in the coming decades, it is anticipated that a mission will be mounted before the mid-point of this century. Not only are the scientific goals very much the same in both cases – a chance to explore a unique environment and search for life beyond Earth – but the benefits will be comparable as well.
With every potentially life-bearing body we explore, we stand to learn more about how life began in our Solar System. And even if we do not find any life in the process, we stand to learn a great deal about the history and formation of the Solar System. On top of that, we will be one step closer to understanding humanity’s place in the Universe.
ASA's Cassini spacecraft looks toward the night side of Saturn's largest moon and sees sunlight scattering through the periphery of Titan's atmosphere and forming a ring of color.
Credit: NASA/JPL-Caltech/Space Science Institute
Last week – from Monday, February 27th to Wednesday, March 1st – NASA hosted the “Planetary Science Vision 2050 Workshop” at their headquarters in Washington, DC. In the course of the many presentations, speeches and panel discussions, NASA’s shared its many plans for the future of space exploration with the international community.
Among the more ambitious of these was a proposal to explore Titan using an aerial explorer and a lander. Building upon the success of the ESA’s Cassini-Huygen mission, this plan would involve a balloon that would explore Titan’s surface from low altitude, along with a Mars Pathfinder-style mission that would explore the surface.
Ultimately, the goal a mission to Titan would be to explore the rich organic chemical environment the moon has, which presents a unique opportunity for planetary researchers. For some time, scientists have understood that Titan’s surface and atmosphere have an abundance of organic compounds and all the prebiotic chemistry necessary for life to function.
Artist depiction of Huygens landing on Titan. Credit: ESA
“Titan’s of particular interest because the abundant and complex organic chemistry can teach us about chemical interactions that could have occurred here on Earth (and elsewhere?) leading to the development of life. Furthermore, not only does Titan have an interior liquid-water ocean, but there will also have been opportunities for organic material to have mixed with liquid water at Titan’s surface, for example impact craters and possibly cryovolcanic eruptions. The combination of organic material with liquid water, of course, increases astrobiological potential.”
For this reason, the exploration of Titan has been a scientific goal for decades. The only question is how best to go about exploring Titan’s unique environment. During previous Decadal Surveys – such as the Campaign Strategy Working Group (CSWG) on Prebiotic Chemistry in the Outer Solar System, of which Lorenz was a contributor – has suggested that a mobile aerial vehicle (such as an airship or a balloon) would well-suited to the task.
However, such vehicles would be unable to study Titan’s methane lakes, which are one of the most exciting draws of the moon as far as research into prebiotic chemistry goes. What’s more, an aerial vehicle would not be able to conduct in-situ chemical analysis of the surface, much like what the Mars Exploration Rovers (Spirit, Opportunity and Curiosity) have been doing on Mars – and with immense results!
The ESA’s TALISE (Titan Lake In-situ Sampling Propelled Explorer) on the left, and NASA’s Titan Mare Explorer (TiME) on the right. Credit: bisbos.com
At the same time, Lorenz and his colleagues examined concepts for the exploration of Titan’s hydrocarbon seas – like the proposed Titan Mare Explorer (TiME) capsule. As one of several finalists of NASA’s 2010 Discovery competition, this concept called for the deployment of nautical robot to Titan in the coming decades, where it would study its methane lakes to learn more about the methane cycle and search for signs of organic life.
While such a proposal would be cost-effective and presents some very exciting opportunities for research, it also has some limitations. For instance, during the 2020s-2030s, Titan’s northern hemisphere will be experiencing its winter season; at which point the thickness of its atmosphere will make direct-to-Earth communications and Earth views impossible. On top of that, a nautical vehicle would preclude the exploration of Titan’s land surfaces.
These offer some of the most likely prospects for studying Titan’s advanced chemical evolution, including Titan’s dune sands. As a windswept region, this area likely has material deposited from all over Titan and may also contain aqueously altered materials. Much as the Mars Pathfinder landing site was selected so it could collect samples from a wide area, such as location would be an ideal site for a lander.
As such, Lorenz and his colleagues advocated the type of mission that was articulated in the 2007 Flagship Study, which called for a Montgolfière balloon for regional exploration and a Pathfinder-like lander. This would provide the opportunity to conduct surface imaging at resolutions that are impossible from orbit (due to the thick atmosphere) as well as investigating the surface chemistry and interior structure of the moon.
Artist’s conception of a possible structure for underground liquid reservoirs on Saturn moon’s Titan. Credit: ESA/ATG medialab
So while the balloon would gather high-resolution geographical data of the moon, the lander could conduct seismological surveys that would characterize the thickness of the ice above Titan’s internal water ocean. However, a lander mission would be limited in terms of range, and the surface of Titan presents problems for mobility. This would make multiple landers, or a relocatable lander, the most desired option.
“Potential targets include areas where we can measure solid surface materials, the composition of which is still not well known, Titan’s dune sands, for example,” said Turtle. “Detailed in situ analysis is required to determine their composition. The lakes and seas are also intriguing; however, in the nearer term (missions arriving in the 2030s) most of those will be in winter darkness. So, exploring them would likely have to wait until the 2040s.”
This mission concept would also take advantage of several technological advances that have been made in recent years. As Lorenz explained in the course of the presentation:
“Heavier-than-air mobility at Titan is in fact highly efficient, moreover, improvements in autonomous aircraft in the two decades since the CSWG make such exploration a realistic prospect. Multiple in-situ landers delivered by an aerial vehicle like an airplane or a lander with aerial mobility to access multiple sites, would provide the most desirable scientific capability, highly relevant to the themes of origins, workings, and life.”
Updated maps of Titan, based on the Cassini imaging science subsystem. Credit: NASA/JPL/Space Science Institute
However, addressing some additional challenges not raised at the 2050 Vision Workshop, they will be presenting a slight twist on their idea. Instead of a balloon and multiple landers, they will present a mission concept involving a “Dragonfly” qaudcopter. This four-rotor vehicle would be able to take advantage of Titan’s thick atmosphere and low gravity to obtain samples and determine the surface composition in multiple geological settings.
This concept also incorporates a lot of recent advances in technology, which include modern control electronics and advances in commerical unmanned aerial vehicle (UAV) designs. On top of that, a quadcopter would do away with chemically-powered retrorockets and could power-up between flights, giving it a potentially much longer lifespan.
These and other concepts for exploring Saturn’s moon Titan are sure to gain traction in the coming years. Given the many mysteries locked away on this world – with includes abundant water ice, prebiotic chemistry, a methane cycle, and a subsurface ocean that is likely to be a prebiotic environment – it is certainly a popular target for scientific research.
Artist depiction of Huygens landing on Titan. Credit: ESA
Twelve years ago today, the Huygens probe landed on Titan, marking the farthest point from Earth any spacecraft has ever landed. While a twelfth anniversary may be an odd number to mark with a special article, as we said in our previous article (with footage from the landing), this is the last opportunity to celebrate the success of Huygens before its partner spacecraft Cassini ends its mission on September 15, 2017 with a fateful plunge into Saturn’s atmosphere.
But Huygens is also worth celebrating because, amazingly, the mission almost failed, but yet was a marvelous success. If not for the insistence of one ESA engineer to complete an in-flight test of Huygens’ radio system, none of the spacecraft’s incredible data from Saturn’s largest and mysterious moon would have ever been received, and likely, no one would have ever known why.
The first-ever images of the surface Titan, taken by the Huygens probe. Image Credit: ESA/NASA/JPL/University of Arizona
As I detail in my new book “Incredible Stories From Space: A Behind-the-Scenes-Look at the Missions Changing Our View of the Cosmos,” in 1999, the Cassini orbiter and the piggybacking Huygens lander were on their way to the Saturn system. The duo launched in 1997, but instead of making a beeline for the 6th planet from the Sun, they took a looping path called the VVEJGA trajectory (Venus-Venus-Earth-Jupiter Gravity Assist), swinging around Venus twice and flying past Earth 2 years later.
While all the flybys gave the spacecraft added boosts to help get it to Saturn, the Earth flyby also provided a chance for the teams to test out various systems and instruments and get immediate feedback.
“The European group wanted to test the Huygens receiver by transmitting the data from Earth,” said Earl Maize, Project Manager for the Cassini mission at JPL, who I interviewed for the book. “That’s a great in-flight test, because there’s the old adage of flight engineers, ‘test as you fly, fly as you test.’”
The way the Huygens mission would work at the Saturn system was that Cassini would release Huygens when the duo approached Titan. Huygens would drop through Titan’s thick and obscuring atmosphere like a skydiver on a parachute, transmitting data all the while. The Huygens probe didn’t have enough power or a large enough dish to transmit all its data directly to Earth, so Cassini would gather and store Huygens’ data on board and later transmit it to Earth.
Boris Smeds was head of ESOC’s Systems and Requirements Section, Darmstadt, Germany. Credit: ESA.
ESA engineer Boris Smeds wanted to ensure this data handoff was going to work, otherwise a crucial part of the mission would be lost. So he proposed a test during the 1999 Earth flyby.
Maize said that for some reason, there was quite a bit of opposition to the test from some of the ESA officials, but Smeds and Claudio Sollazzo, Huygens’s ground operations manager at ESA’s European Space Operation Centre (ESOC) in Darmstadt, Germany were insistent the test was necessary.
NASA’s Deep Space Network is responsible for communicating with spacecraft. Pictured is the Goldstone facility in California, one of three facilities that make up the Network. Image: NASA/JPL
“They were not to be denied,” Maize said, “so they eventually got permission for the test. The Cassini team organized it, going to the Goldstone tracking station [in California] of the Deep Space Network (DSN) and did what’s called a ‘suitcase test,’ broke into the signal, and during the Earth flyby, Huygens, Cassini and Goldstone were all programmed to simulate the probe descending to Titan. It all worked great.”
Except for one thing: Cassini received almost no simulated data, and what it did receive was garbled. No one could figure out why.
Six months of painstaking investigation finally identified the problem. The variation in speed between the two spacecraft hadn’t been properly compensated for, causing a communication problem. It was as if the spacecraft were each communicating on a different frequency.
Artist concept of the Huygens probe descending to Titan. Credit: ESA.
“The European team came to us and said we didn’t have a mission,” Maize said. “But we put together ‘Tiger Teams’ to try and figure it out.”
The short answer was that the idiosyncrasies in the communications system were hardwired in. With the spacecraft now millions of miles away, nothing could be fixed. But engineers came up with an ingenious solution using a basic principal known as the Doppler Effect.
The metaphor Maize likes to use is this: if you are sitting on the shore and a speed boat goes by close to the coast, it zooms past you quickly. But that same boat going the same speed out on the horizon looks like it is barely moving.
“Since we couldn’t change Huygens’ signal, the only thing we could change was the way Cassini flew,” Maize said. “If we could move Cassini farther away and make it appear as if Huygens was moving slower, it would receive lander’s radio waves at a lower frequency, solving the problem.”
Maize said it took two years of “fancy coding modifications and some pretty amazing trajectory computations.” Huygens’ landing was also delayed two months for the new trajectory that was needed overcome the radio system design flaw.
Additionally, with Cassini needing to be farther away from Huygens than originally planned, it would eventually fly out of range to capture all of Huygens’ data. Astronomers instigated a plan where radio telescopes around the world would listen for Huygens’ faint signals and capture anything Cassini missed.
Huygens was released from the Cassini spacecraft on Christmas Day 2004, and arrived at Titan on January 14, 2005. The probe began transmitting data to Cassini four minutes into its descent through Titan’s murky atmosphere, snapping photos and taking data all the while. Then it touched down, the first time a probe had landed on an extraterrestrial world in the outer Solar System.
Because of the communication problem, Huygens was not able to gather as much information as originally planned, as it could only transmit on one channel instead of two. But amazingly, Cassini captured absolutely all the data sent by Huygens until it flew out of range.
“It was beautiful,” Maize said, “I’ll never forget it. We got it all, and it was a wonderful example of international cooperation. The fact that 19 countries could get everything coordinated and launched in the first place was pretty amazing, but there’s nothing that compares to the worldwide effort we put into recovering the Huygens mission. From an engineering standpoint, that might trump everything else we’ve done on this mission.”
The view of Titan from the descending Huygens spacecraft on January 14, 2005. Credit: ESA/NASA/JPL/University of Arizona.
With its ground-breaking mission, Huygens provided the first real view of the surface of Titan. The data has been invaluable for understanding this unique and mysterious moon, showing geological and meteorological processes that are more similar to those on the surface of the Earth than anywhere else in the Solar System. ESA has details on the top discoveries by Huygens here.
Noted space journalist Jim Oberg has written several detailed and very interesting articles about the Huygens’ recovery, including one at IEEE Spectrum and another at The Space Review. These articles provide much more insight into the test, Smeds’ remarkable insistence for the test, the recovery work that was done and the subsequent success of the mission.
As Oberg says in IEEE Spectrum, “Smeds continued a glorious engineering tradition of rescuing deep-space missions from doom with sheer persistence, insight, and lots of improvisation.”
A modest Smeds was quoted by ESA: “This has happened before. Almost any mission has some design problem,” says Smeds, who says he’s worked on recovering from pre- and post-launch telecom issues that have arisen with several past missions. “To me, it’s just part of my normal work.”
For more stories about Huygens, Cassini and several other current robotic space missions, “Incredible Stories From Space” tells many behind-the-scenes stories from the amazing people who work on these missions.
The view of Titan from the descending Huygens spacecraft on January 14, 2005. Credit: ESA/NASA/JPL/University of Arizona.
On December 25, 2004, the piggybacking Huygens probe was released from the ‘mothership’ Cassini spacecraft and it arrived at Titan on January 14, 2005. The probe began transmitting data to Cassini four minutes into its descent through Titan’s murky atmosphere, snapping photos and taking data all the while. Then it touched down, the first time a probe had landed on an extraterrestrial world in the outer Solar System.
JPL has released a re-mix of the data and images gathered by Huygens 12 years ago in a beautiful new video. This is the last opportunity to celebrate the success of Huygens before Cassini ends its mission in September of 2017.
Watch as the incredible view of Titan’s surface comes into view, with mountains, a system of river channels and a possible lakebed.
After a two-and-a-half-hour descent, the metallic, saucer-shaped spacecraft came to rest with a thud on a dark floodplain covered in cobbles of water ice, in temperatures hundreds of degrees below freezing.
Huygens had to quickly collect and transmit all the images and data it could because shortly after landing, Cassini would drop below the local horizon, “cutting off its link to the home world and silencing its voice forever.”
How much of this video is actual images and data vs computer graphics?
Of course, the clips at the beginning and end of the video are obviously animations of the probe and orbiter. However, the slow descending 1st-person point-of-view video is made using actual images from Huygens. But Huygens did not take a continuous movie sequence, so a lot of work was done by the team that operated Huygens’ optical imager, the Descent Imager/Spectral Radiometer (DISR), to enhance, colorize, and re-project the images into a variety of formats.
The view of the cobblestones and the parachute shadow near the end of the video is also created from real landing data, but was made in a different way from the rest of the descent video, because Huygens’ cameras did not actually image the parachute shadow. However, the upward looking infrared spectrometer took a measurement of the sky every couple of seconds, recording a darkening and then brightening to the unobstructed sky. The DISR team calculated from this the accurate speed and direction of the parachute, and of its shadow to create a very realistic video based on the data.
If you’re a data geek, there are some great videos of Huygens’ data by the University of Arizona Lunar and Planetary Laboratory team, such as this one:
The movie shows the operation of the DISR camera during the descent onto Titan. The almost 4-hour long operation
of DISR is shown in less than five minutes in 40 times actual sped up to landing and 100 times actual speed thereafter.
Erich Karkoschka from the UA team explained what all the sounds in the video are. “All parts of DISR worked together as programmed, creating a harmony,” he said. Here’s the full explanation:
Sound was added to mark various events. The left speaker follows the motion of Huygens. The pitch of the tone indicates the rotational speed. Vibrato indicates vibration of the parachute. Little clicks indicate the clocking of the rotation counter. Noise corresponds to heating of the heat shield, to parachute deployments, to the heat shield release, to the jettison of the DISR cover, and to touch down.
The sound in the right speaker follows DISR data. The pitch of the continuous tone goes with the signal strength. The 13 different chime tones indicate activity of the 13 components of DISR. The counters at the top and bottom of the list get the high and low notes, respectively.
You can see more info and videos created from Huygens’ data here.
In this near-infrared mosaic, the sun shines off of the seas on Saturn's moon, Titan. Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho
Titan is tough moon to study, thanks to its incredibly thick and hazy atmosphere. But when astronomers have ben able to sneak a peak beneath its methane clouds, they have spotted some very intriguing features. And some of these, interestingly enough, are reminiscent of geographical features here on Earth. For instance, Titan is the only other body in the Solar System that is known to have a cycle where liquid is exchanged between the surface and the atmosphere.
For example, previous images provided by NASA’s Cassini mission showed indications of steep-sided canyons in the northern polar region that appeared to be filled with liquid hydrocarbons, similar to river valleys here on Earth. And thanks to new data obtained through radar altimetry, these canyons have been shown to be hundreds of meters deep, and have confirmed rivers of liquid methane flowing through them.
This evidence was presented in a new study titled “Liquid-filled canyons on Titan” – which was published in August of 2016 in the journal Geophysical Research Letters. Using data obtained by the Cassini radar altimeter in May 2013, they observed channels in the feature known as Vid Flumina, a drainage network connected to Titan’s second largest hydrocarbon sea in the north, Ligeia Mare.
Saturn’s largest moon, Titan, has features that resemble Earth’s geology, with deep, steep-sided canyons. Credit: NASA/JPL/Cassini
Analysis of this information showed that the channels in this region are steep-sided and measure about 800 m (half a mile) wide and between 244 and 579 meters deep (800 – 1900 feet). The radar echoes also showed strong surface reflections that indicated that these channels are currently filled with liquid. The elevation of this liquid was also consistent with that of Ligeia Mare (within a maring of 0.7 m), which averages about 50 m (164 ft) deep.
This is consistent with the belief that these river channels in area drain into the Ligeia Mare, which is especially interesting since it parallels how deep-canyon river systems empty into lakes here on Earth. And it is yet another example of how the methane-based hydrological cycle on Titan drives the formation and evolution of the moon’s features, and in ways that are strikingly similar to the water cycle here on Earth.
Alex Hayes – an assistant professor of astronomy at Cornell, the Director of the Spacecraft Planetary Imaging Facility (SPIF) and one of the authors on the paper – has conducted seversal studies of Titan’s surface and atmosphere based on radar data provided by Cassini. As he was quoted as saying in a recent article by the Cornell Chronicler:
“Earth is warm and rocky, with rivers of water, while Titan is cold and icy, with rivers of methane. And yet it’s remarkable that we find such similar features on both worlds. The canyons found in Titan’s north are even more surprising, as we have no idea how they formed. Their narrow width and depth imply rapid erosion, as sea levels rise and fall in the nearby sea. This brings up a host of questions, such as where did all the eroded material go?”
Cassini image of the northern polar area of Titan and Vid Flumina drainage basin, showing Ligeia Mare (left) and the Vid Flumina drainage basin (right). Credit: R.L. Kirk/NASA/JPLA good question indeed, since it raises some interesting possibilities. Essentially, the features observed by Cassini are just part of Titan’s northern polar region, which is covered by large standing bodies of liquid methane – the largest of these being Kraken Mare, Ligeia Mare and Punga Mare. In this respect, the region is similar to glacially eroded fjords on Earth.
However, conditions on Titan do not allow for the presence of glaciers, which rules out the likelihood that retreating sheets of ice could have carved these canyons. So this naturally begs the question, what geological forces created this region? The team concluded that there were only two likely possibilities – which included changes in the elevation of the rivers, or tectonic activity in the area.
Ultimately, they favored a model where the variation in surface elevation of liquid drove the formation of the canyons – though they acknowledge that both tectonic forces and sea level variations played a role. As Valerio Poggiali, an associate member of the Cassini RADAR Science Team at the Sapienza University of Rome and the lead author of the paper, told Universe Today via email:
“What the canyons on Titan really mean is that in the past sea level was lower and so erosion and canyon formation could take place. Subsequently sea level has risen and backfilled the canyons. This presumably takes place over multiple cycles, eroding when sea level is lower, depositing some when it is higher until we get the canyons we see today. So, what it means is that sea level has likely changed in the geological past and the canyons are recording that change for us.”
Titan’s second largest methane lake, Ligeia Mare. Credit: NASA/JPL/USGS
In this respect, there are many more Earth examples to choose from, all of which are mentioned in the study:
“Examples include Lake Powell, a reservoir on the Colorado River that was created by the Glen Canyon Dam; the Georges River in New South Wales, Australia; and the Nile River gorge, which formed as the Mediterranean Sea dried up during the late Miocene. Rising liquid levels in the geologically recent past led to the flooding of these valleys, with morphologies similar to those observed at Vid Flumina.”
Understanding the processes that led to these formations is crucial to understanding the current state of Titan’s geomorphology. And this study is significant in that it is the first to conclude that the rivers in the Vid Flumina region were deep canyons. In the future, the research team hopes to examine other channels on Titan that were observed by Cassini to test their theories.
Once again, our exploration of the Solar System has shown us just how weird and wonderful it truly is. In addition to all its celestial bodies having their own particular quirks, they still have a lot in common with Earth. By the time the Cassini mission is complete (Sept. 15th, 2017), it will have surveyed 67% the surface of Titan with its RADAR imaging instrument. Who knows what other “Earth-like” features it will notice before then?
A halo of light surrounds Saturn's moon Titan in this backlit picture, showing its atmosphere. Credit: NASA/JPL/Space Science Institute
Ever since the Cassini probe arrived at Saturn in 2004, it has revealed some startling things about the planet’s system of moons. Titan, Saturn’s largest moon, has been a particular source of fascination. Between its methane lakes, hydrocarbon-rich atmosphere, and the presence of a “methane cycle” (similar to Earth’s “water cycle”), there is no shortage of fascinating things happening on this Cronian moon.
As if that wasn’t enough, Titan also experiences seasonal changes. At present, winter is beginning in the southern hemisphere, which is characterized by the presence of a strong vortex in the upper atmosphere above the south pole. This represents a reversal of what the Cassini probe witnessed when it first started observing the moon over a decade ago, when similar things were happening in the northern hemisphere.
The large cloud in the stratosphere over Titan’s north pole (left) is similar to Earth’s polar stratospheric clouds (right). Credit: L. NASA/JPL/U. of Ariz./LPGNantes; R. NASA/GSFC/M. Schoeberl
During the course of the meeting, Dr. Athena Coustenis – the Director of Research (1st class) with the National Center for Scientific Research (CNRS) in France – shared the latest atmospheric data retrieved by Cassini. As she stated:
“Cassini’s long mission and frequent visits to Titan have allowed us to observe the pattern of seasonal changes on Titan, in exquisite detail, for the first time. We arrived at the northern mid-winter and have now had the opportunity to monitor Titan’s atmospheric response through two full seasons. Since the equinox, where both hemispheres received equal heating from the Sun, we have seen rapid changes.”
Scientists have been aware of seasonal change on Titan for some time. This is characterized by warm gases rising at the summer pole and cold gases settling down at the winter pole, with heat being circulated through the atmosphere from pole to pole. This cycle experiences periodic reversals as the seasons shift from one hemisphere to the other.
In 2009, Cassini observed a large scale reversal immediately after the equinox of that year. This led to a temperature drop of about 40 °C (104 °F) around the southern polar stratosphere, while the northern hemisphere experienced gradual warming. Within months of the equinox, a trace gas vortex appeared over the south pole that showed glowing patches, while a similar feature disappeared from the north pole.
High in the atmosphere of Titan, large patches of two trace gases glow near the north pole, on the dusk side of the moon, and near the south pole, on the dawn side. Credit: NRAO/AUI/NSF
A reversal like this is significant because it gives astronomers a chance to study Titan’s atmosphere in greater detail. Essentially, the southern polar vortex shows concentrations of trace gases – like complex hydrocarbons, methylacetylne and benzene – which accumulate in the absence of UV light. With winter now upon the southern hemisphere, these gases can be expected to accumulate in abundance.
As Coustenis explained, this is an opportunity for planetary scientists to test out their models for Titan’s atmosphere:
“We’ve had the chance to witness the onset of winter from the beginning and are approaching the peak time for these gas-production processes in the southern hemisphere. We are now looking for new molecules in the atmosphere above Titan’s south polar region that have been predicted by our computer models. Making these detections will help us understand the photochemistry going on.”
Previously, scientists had only been able to observe these gases at high northern latitudes, which persisted well into summer. They were expected to undergo slow photochemical destruction, where exposure to light would break them down depending on their chemical makeup. However, during the past few months, a zone of depleted molecular gas and aerosols has developed at an altitude of between 400 and 500 km across the entire northern hemisphere .
Titan’s south polar vortex. Credit: NASA/JPL-Caltech/Space Science Institute
This suggests that, at high altitudes, Titan’s atmosphere has some complex dynamics going on. What these could be is not yet clear, but those who have made the study of Titan’s atmosphere a priority are eager to find out. Between now and the end of Cassini mission (which is slated for Sept. 2017), it is expected that the probe will have provided a complete picture of how Titan’s middle and upper atmospheres behave.
By mission’s end, the Cassini space probe will have conducted more than 100 targeted flybys of Saturn. In so doing, it has effectively witnessed what a full year on Titan looks like, complete with seasonal variability. Not only will this information help us to understand the deeper mysteries of one of the Solar System’s most mysterious moons, it should also come in handy if and when we send astronauts (and maybe even settlers) there someday!
![The northern polar area of Titan and Vid Flumina drainage basin. (left) On top of the image, the Ligeia Mare; in the lower right the North Kraken Mare; the two seas are connected each other by a labyrinth of channels. On the left, near the North pole, the Punga Mare. Red arrows indicate the position of the two flumina significant for this work. At the end of its mission (15 September 2017) the Cassini RADAR in its imaging mode (SAR+ HiSAR) will have covered a total area of 67% of the surface of Titan [Hayes, 2016]. Map credits: R. L. Kirk. (right) Highlighted in yellow are the half-power altimetric footprints within the Vid Flumina drainage basin and the Xanthus Flumen course for which specular reflections occurred. At 1400?km of spacecraft altitude, the Cassini antenna 0.35° central beam produces footprints of about 8.5?km in diameter (diameter of yellow circles). Credit: NASA/JPL](https://www.universetoday.com/wp-content/uploads/2016/11/grl54735-fig-0001.png)
