Titan Archives - Page 5 of 17

March 11, 2017March 11, 2017

Exploring Titan with Aerial Platforms

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.

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.

Further Reading: USRA

March 7, 2017April 30, 2017

Exploring Titan with Balloons and Landers

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*

The presentation, which was titled “Aerial Mobility : The Key to Exploring Titan’s Rich Chemical Diversity” was chaired by Ralph Lorenz from the Johns Hopkins Applied Physics Laboratory, and co-chaired by Elizabeth Turtle (also from John Hopkins APL) and Jason Barnes from the Dept. of Physics at the University of Idaho. As Turtle explained to Universe Today via email, Titan presents some exciting opportunities for a next-generation mission:

“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*

Lorenz, Turtle and Barnes will also be presenting these findings at the upcoming 48th Lunar and Planetary Science Conference – which will be taking place from March 20th to 24th in The Woodlands, Texas. There they will be joined by additional members of the Johns Hopkins APL and the University of Idaho, as well as panelists from NASA’s Goddard Space Flight Center, Pennsylvania State University, and Honeybee Robotics.

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.

Further Reading: USRA, USRA (2), USRA (3)

January 14, 2017September 28, 2017

The Incredible Story of How the Huygens Mission to Titan Succeeded When It Could Have Failed

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 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 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 Juno as it explores Jupiter. Pictured is the Goldstone facility in California, one of three facilities that make up the Network. Image: NASA/JPL — 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.

January 12, 2017

Land On Titan With Huygens in Beautiful New Video

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.

Read some reminiscences about Huygens from some of the Cassini team here.

November 1, 2016November 2, 2016

Even Though it’s an Alien World, Titan’s Canyons Would Look Very Familiar

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 — *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?”

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 — *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/JPL*

A 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 Ligeia Mare. Credit: NASA/JPL/USGS — *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?

Further Reading: Geophysical Research Letters

October 24, 2016November 5, 2016

Seasonal Change On Titan Is Dynamic Business

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.

These finding were shared at the joint 48th meeting of the American Astronomical Society’s Division for Planetary Sciences and 11th European Planetary Science Congress, which took place from Oct 16th to 21st in Pasadena, California. As the second joint conference between these bodies, the goal of this annual meeting is to strengthen international scientific collaboration in the field of planetary science.

This cloud in the stratosphere over Titan’s north pole (left) is similar to Earth’s polar stratospheric clouds (right). NASA scientists found that Titan’s cloud contains methane ice, which was not previously thought to form in that part of the atmosphere. Cassini first spotted the cloud in 2006. Image Credit: L. NASA/JPL/U. of Ariz./LPGNantes; R. NASA/GSFC/M. Schoeberl — *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 (1^st 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. Brighter colors indicate stronger signals from the two gases, HNC (left) and HC3N (right); red hues indicate less pronounced signals. Image (Credit: NRAO/AUI/NSF) — *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 .

View of Titan's South Pole, showing a vortex. Credit: NASA — *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!

Further Reading: Europlanet

July 6, 2016September 20, 2016

Life On Titan Possible Without Water

Saturn’s largest moon Titan is a truly fascinating place. Aside from Earth, it is the only place in the Solar System where rainfall occurs and there are active exchanges between liquids on the surface and fog in the atmosphere – albeit with methane instead of water. It’s atmospheric pressure is also comparable to Earth’s, and it is the only other body in the Solar System that has a dense atmosphere that is nitrogen-rich.

For some time, astronomers and planetary scientists have speculated that Titan might also have the prebiotic conditions necessary for life. Others, meanwhile, have argued that the absence of water on the surface rules out the possibility of life existing there. But according to a recent study produced by a research team from Cornell University, the conditions on Titan’s surface might support the formation of life without the need for water.

When it comes to searching for life beyond Earth, scientists focus on targets that possess the necessary ingredients for life as we know it – i.e. heat, a viable atmosphere, and water. This is essentially the “low-hanging fruit” approach, where we search for conditions resembling those here on Earth. Titan – which is very cold, quite distant from our Sun, and has a thick, hazy atmosphere – does not seem like a viable candidate, given these criteria.

*Diagram of the internal structure of Titan according to the fully differentiated dense-ocean model. Credit: Wikipedia Commons/Kelvinsong*

However, according to the Cornell research team – which is led by Dr. Martin Rahm – Titan presents an opportunity to see how life could emerge under different conditions, one which are much colder than Earth and don’t involve water.

Their study – titled “Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan” – appeared recently in the Proceedings of the National Academy of Sciences (PNAS). In it, Rahm and his colleagues examined the role that hydrogen cyanide, which is believed to be central to the origin of life question, may play in Titan’s atmosphere.

Previous experiments have shown that hydrogen cyanide (HCN) molecules can link together to form polyimine, a polymer that can serve as a precursor to amino acids and nucleic acids (the basis for protein cells and DNA). Previous surveys have also shown that hydrogen cyanide is the most abundant hydrogen-containing molecule in Titan’s atmosphere.

As Professor Lunine – the David C. Duncan Professor in the Physical Sciences and Director of the Cornell Center for Astrophysics and Planetary Science and co-author of the study – told Universe Today via email: “Organic molecules, liquid lakes and seas (but of methane, not water) and some amount of solar energy reaches the surface. So this suggests the possibility of an environment that might host an exotic form of life.”

What other surprises may be found beneath Titan's thick haze and clouds? (NASA/JPL/SSI/J. Major) — *Titan’s thick, hazy atmosphere may conceal clues as to the possibility of life-giving conditions on its surface. Credit: NASA/JPL/SSI/J. Major*

Using quantum mechanical calculations, the Cornell team showed that polyimine has electronic and structural properties that could facilitate prebiotic chemistry under very cold conditions. These involve the ability to absorb a wide spectrum of light, which is predicted to occur in a window of relative transparency in Titan’s atmosphere.

Another is the fact that polyimine has a flexible backbone, and can therefore take on many different structures (aka. polymorphs). These range from flat sheets to complex coiled structures, which are relatively close in energy. Some of these structures, according to the team, could work to accelerate prebiotic chemical reactions, or even form structures that could act as hosts for them.

“Polyimine can form sheets,” said Lunine, “which like clays might serve as a catalytic surface for prebiotic reactions. We also find the polyimine absorbs sunlight where Titan’s atmosphere is quite transparent, which might help to energize reactions.”

In short, the presence of polyimine could mean that Titan’s surface gets the energy its needs to drive photochemical reactions necessary for the creation of organic life, and that it could even assist in the development of that life. But of course, no evidence has been found that polyimine has been produced on the surface of Titan, which means that these research findings are still academic at this point.

On the left is TALISE (Titan Lake In-situ Sampling Propelled Explorer), the ESA proposal. This would have it's own propulsion, in the form of paddlewheels. Credit: bisbos.com — *Proposed missions to Titan have included (from left to right) the TALISE (Titan Lake In-situ Sampling Propelled Explorer) and NASA’s Titan Mare Explorer. Credit: bisbos.com*

However, Lunine and his team indicate that hydrogen cyanide may very well have lead to the creation of polyimine on Titan, and that it might have simply escaped detection because of Titan’s murky atmosphere. They also added that future missions to Titan might be able to look for signs of the polymer, as part of ongoing research into the possibility of exotic life emerging in other parts of the Solar System.

“We would need an advanced payload on the surface to sample and search for polyimines,” answered Lunine, “or possibly by a next generation spectrometer from orbit. Both of these are “beyond Cassini”, that is, the next generation of missions.”

Perhaps when Juno is finished surveying Jupiter’s atmosphere in two years time, NASA might consider retasking it for a flyby of Titan? After all, Juno was specifically designed to peer beneath a veil of thick clouds. They don’t come much thicker than on Titan!

Further Reading: PNAS

March 3, 2016March 18, 2016

Surfing On Titan Would Be Best In Summer

The view from the beach on Titan? Image: NASA

Space is mostly vast and empty. So whenever we notice something like ripples on a lake, on the frozen moon of a gas giant, we take notice.

At a meeting of the American Geophysical Union in San Francisco this week, it was reported that Cassini images of Saturn’s moon Titan showed light being reflected from the Ligeia Mare, a frigid sea of hydrocarbons on that moon. Subsequent images showed the same phenomenon on two other seas of Titan, as well. These are thought to be waves, the first waves detected anywhere other than Earth, and suggest that Titan has more geophysical activity than previously thought.

Surfers on Earth, known for seeking out remote and secretive locations, shouldn’t get too excited. According to mathematical modelling and radar imagery, these waves are only 1.5 cm (0.6 inches) tall, and they’re moving only 0.7 metres (2.3 feet) per second. Plus, they’re on a sea of liquid hydrocarbons—mostly methane—that is a frigid -180 degrees Celsius (-292 F.)

Planetary scientists are taking note, though, because these waves show that Titan has an active environment, rather than just being a moon frozen in time. It’s thought that the change in seasons on Titan is responsible for these waves, as Titan begins its 7 year summer. Processes related to the changing seasons on Titan have created winds, which have cause these ripples.

There’s other evidence of active weather on Titan, including dunes, river channels, and shorelines. But this is the first observation of active weather phenomena, rather than just the results. All together, it shows that Titan is a more active, dynamic environment than previously thought.

Titan’s hydrocarbon lakes are thought to be up to 200 metres (656 ft.) deep, and are clustered around the north polar region. Just one of its lakes is thought to contain approximately 9,000 cubic km of methane, which is about 40 times more than the Earth’s reserves of oil and gas.

Titan is the second largest moon in the Solar System, second only to Ganymede, and both moons are larger than the planet Mercury. Titan was discovered in 1655 by Christiaan Huygens.

October 2, 2015December 23, 2015

Is There a Kraken in Kraken Mare? What Kind of Life Would We Find on Titan?

Could there be life on Saturn’s large moon Titan? Asking the question forces astrobiologists and chemists to think carefully and creatively about the chemistry of life, and how it might be different on other worlds than it is on Earth. In February, a team of researchers from Cornell University, including chemical engineering graduate student James Stevenson, planetary scientist Jonathan Lunine, and chemical engineer Paulette Clancy, published a pioneering study arguing that cell membranes could form under the exotic chemical conditions present on this remarkable moon.

In many ways, Titan is Earth’s twin. It’s the second largest moon in the solar system and bigger than the planet Mercury. Like Earth, it has a substantial atmosphere, with a surface atmospheric pressure a bit higher than Earth’s. Besides Earth, Titan is the only object in our solar system known to have accumulations of liquid on its surface. NASA’s Cassini space probe discovered abundant lakes and even rivers in Titan’s polar regions. The largest lake, or sea, called Kraken Mare, is larger than Earth’s Caspian Sea. Researchers know from both spacecraft observations and laboratory experiments that Titan’s atmosphere is rich in complex organic molecules, which are the building blocks of life.

All these features might make it seem as though Titan is tantalizingly suitable for life. The name ‘Kraken’, which refers to a legendary sea monster, fancifully reflects the eager hopes of astrobiologists. But, Titan is Earth’s alien twin. Being almost ten times further from the sun than Earth is, its surface temperature is a frigid -180 degrees Celsius. Liquid water is vital to life as we know it, but on Titan’s surface all water is frozen solid. Water ice takes on the role that silicon-containing rock does on Earth, making up the outer layers of the crust.

The liquid that fills Titan’s lakes and rivers is not water, but liquid methane, probably mixed with other substances like liquid ethane, all of which are gases here on Earth. If there is life in Titan’s seas, it is not life as we know it. It must be an alien form of life, with organic molecules dissolved in liquid methane instead of liquid water. Is such a thing even possible?

The Cornell team took up one key part of this challenging question by investigating whether cell membranes can exist in liquid methane. Every living cell is, essentially, a self-sustaining network of chemical reactions, contained within bounding membranes. Scientists think that cell membranes emerged very early in the history of life on Earth, and their formation might even have been the first step in the origin of life.

Here on Earth, cell membranes are as familiar as high school biology class. They are made of large molecules called phospholipids. Each phospholipid molecule has a ‘head’ and a ‘tail’. The head contains a phosphate group, with a phosphorus atom linked to several oxygen atoms. The tail consists of one or more strings of carbon atoms, typically 15 to 20 atoms long, with hydrogen atoms linked on each side. The head, due to the negative charge of its phosphate group, has an unequal distribution of electrical charge, and we say that it is polar. The tail, on the other hand, is electrically neutral.

phospholipid membrane — Here on Earth, cell membranes are composed of phospholipid molecules dissolved in liquid water. A phospholipid has a backbone of carbon atoms (gray), and also contains hydrogen (sky blue), phosphorus (yellow), oxygen (red), and nitrogen (blue). Due to the positive charge associated with the nitrogen containing choline group, and the negative charge associated with the phosphate group, the head is polar, and attracts water. It is therefore hydrophilic. The hydrocarbon tail is electrically neutral and hydrophobic. The structure of a cell membrane is due these electrical properties of phospholipids and water. The molecules form a double layer, with the hydrophilic heads facing outward, towards water, and the hydrophobic tails facing inward, towards one another. Credit: Ties van Brussel

These electrical properties determine how phospholipid molecules will behave when they are dissolved in water. Electrically speaking, water is a polar molecule. The electrons in the water molecule are more strongly attracted to its oxygen atom than to its two hydrogen atoms. So, the side of the molecule where the two hydrogen atoms are has a slight positive charge, and the oxygen side has a small negative charge. These polar properties of water cause it to attract the polar head of the phospholipid molecule, which is said to be hydrophilic, and repel its nonpolar tail, which is said to be hydrophobic.

When phospholipid molecules are dissolved in water, the electrical properties of the two substances work together to cause the phospholipid molecules to organize themselves into a membrane. The membrane closes onto itself into a little sphere called a liposome. The phospholipid molecules form a bilayer two molecules thick. The polar hydrophilic heads face outward towards the water on both the inner and outer surface of the membrane. The hydrophobic tails are sandwiched between, facing each other. While the phospholipid molecules remain fixed in their layer, with their heads facing out and their tails facing in, they can still move around with respect to each other, giving the membrane the fluid flexibility needed for life.

Phospholipid bilayer membranes are the basis of all terrestrial cell membranes. Even on its own, a liposome can grow, reproduce and aid certain chemical reactions important to life, which is why some biochemists think that the formation of liposomes might have been the first step towards life. At any rate, the formation of cell membranes must surely been an early step in life’s emergence on Earth.

water and methane — At the left, water, consisting of hydrogen (H) and oxygen (O), is a polar solvent. Oxygen attracts electrons more strongly than hydrogen does, giving the hydrogen side of the molecule a net positive charge and the oxygen side a net negative charge. The delta symbol ( ) indicates that the charge is partial, that is less than a full unit of positive or negative charge. At right, methane is a non-polar solvent, due to the symmetrical distribution of hydrogen atoms (H) around a central carbon atom (C). Credit: Jynto as modified by Paul Patton.

If some form of life exists on Titan, whether sea monster or (more likely) microbe, it would almost certainly need to have a cell membrane, just like every living thing on Earth does. Could phospholipid bilayer membranes form in liquid methane on Titan? The answer is no. Unlike water, the methane molecule has an even distribution of electrical charges. It lacks water’s polar qualities, and so couldn’t attract the polar heads of phospholipid molecule. This attraction is needed for the phospholipids to form an Earth-style cell membrane.

Experiments have been conducted where phospholipids are dissolved in non-polar liquids at Earthly room temperature. Under these conditions, the phospholipids form an ‘inside-out’ two layer membrane. The polar heads of the phospholipid molecules are at the center, attracted to one another by their electrical charges. The non-polar tails face outward on each side of the inside-out membrane, facing the non-polar solvent.

membranes in polar and non-polar solvents — At left, phospholipids are dissolved in water, a polar solvent. They form a bilayer membrane, with their polar, hydrophilic heads facing outward towards water, and their hydrophobic tails facing each other. At right, when phospholipids are dissolved in a non-polar solvent at Earthly room temperature, they form an inside-out membrane, with the polar heads attracting one another, and the non-polar tails facing outwards towards the non-polar solvent. Based on figure 2 from Stevenson, Lunine, and Clancy (2015). Credit: Paul Patton

Could Titanian life have an inside out phospholipid membrane? The Cornell team concluded that this wouldn’t work, for two reasons. The first is that at the cryogenic temperatures of liquid methane, the tails of phospholipids become rigid, depriving any inside-out membrane that might form of the fluid flexibility needed for life. The second is that two key ingredients of phospholipids; phosphorus and oxygen, are probably unavailable in the methane lakes of Titan. In their search for Titanian cell membranes, the Cornell team needed to probe beyond the familiar realm of high school biology.

Although not composed of phospholipids, the scientists reasoned that any Titanian cell membrane would nevertheless be like the inside-out phospholipid membranes created in the lab. It would consist of polar molecules clinging together electrically in a solution of non-polar liquid methane. What molecules might those be? For answers the researchers looked to data from the Cassini spacecraft and from laboratory experiments that reproduced the chemistry of Titan’s atmosphere.

Titan’s atmosphere is known to have a very complex chemistry. It is made mostly of nitrogen and methane gas. When the Cassini spacecraft analyzed its composition using spectroscopy it found traces of a variety of compounds of carbon, nitrogen, and hydrogen, called nitriles and amines. Researchers have simulated the chemistry of Titan’s atmosphere in the lab by exposing mixtures of nitrogen and methane to sources of energy simulating sunlight on Titan. A stew of organic molecules called ‘tholins’ is formed. It consists of compounds of hydrogen and carbon, called hydrocarbons, as well as nitriles and amines.

The Cornell investigators saw nitriles and amines as potential candidates for their Titanian cell membranes. Both are polar molecules that might stick together to form a membrane in non-polar liquid methane due to the polarity of nitrogen containing groups found in both of them. They reasoned that candidate molecules must be much smaller than phospholipids, so that they could form fluid membranes at liquid methane temperatures. They considered nitriles and amines containing strings of between three and six carbon atoms. Nitrogen containing groups are called ‘azoto’ –groups, so the team named their hypothetical Titanian counterpart to the liposome the ‘azotosome’.

Synthesizing azotosomes for experimental study would have been difficult and expensive, because the experiments would need to be conducted at the cryogenic temperatures of liquid methane. But since the candidate molecules have been studied extensively for other reasons, the Cornell researchers felt justified in turning to the tools of computational chemistry to determine whether their candidate molecules could cohere as a flexible membrane in liquid methane. Computational models have been used successfully to study conventional phospholipid cell membranes.

acrylonitrile — Acrylonitrile has been identified as a possible basis for cell membranes in liquid methane on Titan. It is known to be present in Titan’s atmosphere at a concentration of 10 parts per million and has been produced in laboratory simulations of the effects of energy sources on Titan’s nitrogen-methane atmosphere. As a small polar molecule capable of dissolving in liquid methane, it is a candidate substance for the formation of cell membranes in an alternative biochemistry on Titan. Light blue: carbon atoms, dark blue: nitrogen atom, white: hydrogen atoms. Credit: Ben Mills as modified by Paul Patton.

acrylonitrile membrane — Polar acrylonitrile molecules align ‘head’ to ‘tail’ to form a membrane in non-polar liquid methane. Light blue: carbon atoms, dark blue: nitrogen atoms, white: hydrogen atoms. Credit: James Stevenson.

The group’s computational simulations showed that some candidate substances could be ruled out because they would not cohere as a membrane, would be too rigid, or would form a solid. Nevertheless, the simulations also showed that a number of substances would form membranes with suitable properties. One suitable substance is acrylonitrile, which Cassini showed is present in Titan’s atmosphere at 10 parts per million concentration. Despite the huge difference in temperature between cryogenic azotozomes and room temperature liposomes, the simulations showed them to exhibit strikingly similar properties of stability and response to mechanical stress. Cell membranes, then, are possible for life in liquid methane.

Computational chemistry simulations show that acrylonitrile and some other small polar nitrogen containing organic molecules are capable of forming ‘azotosomes’ when they are dissolved on liquid methane. Azotosomes are small membrane bounded spherules like the liposomes formed by phospholipids when they are dissolved in water. The simulations show that acrylonitrile azotosomes would be both stable and flexible in cryogenically cold liquid methane, giving them the properties they need to function as cell membranes for hypothetical Titanian life, or for life on any world with liquid methane on its surface. The azotosome shown is 9 nanometers in size, about the size of a virus. Light blue: carbon atoms, dark blue: nitrogen atoms, white: hydrogen atoms. Credit: James Stevenson.

The scientists from Cornell view their findings as nothing more than a first step towards showing that life in liquid methane is possible, and towards developing the methods that future spacecraft will need to search for it on Titan. If life is possible in liquid methane, the implications ultimately extend far beyond Titan.

When seeking conditions suitable for life in the galaxy, astronomers typically search for exoplanets within a star’s habitable zone, defined as the narrow range of distances over which a planet with an Earth-like atmosphere would have a surface temperature suitable for liquid water. If methane life is possible, then stars would also have a methane habitable zone, a region where methane could exist as a liquid on a planet or moon, making methane life possible. The number of habitable worlds in the galaxy would be greatly increased. Perhaps, on some worlds, methane life evolves into complex forms that we can scarcely imagine. Maybe some of them are even a bit like sea monsters.

References and Further Reading:

N. Atkinson (2010) Alien Life on Titan? Hang on Just a Minute, Universe Today.

N. Atkinson (2010) Life on Titan Could be Smelly and Explosive, Universe Today.

M. L. Cable, S. M. Horst, R. Hodyss, P. M. Beauchamp, M. A. Smith, P. A. Willis, (2012) Titan tholins: Simulating Titan organic chemistry in the Cassini-Huygens era, Chemical Reviews, 112:1882-1909.

E. Howell (2014) Titan’s Majestic Mirror-Like Lakes Will Come Under Cassini’s Scrutiny This Week, Universe Today.

J. Major (2013) Titan’s North Pole is Loaded With Lakes, Universe Today.

C. P. McKay, H. D. Smith, (2005) Possibilities for methanogenic life in liquid methane on the surface of Titan, Icarus 178: 274-276.

J. Stevenson, J. Lunine, P. Clancy, (2015) Membrane alternatives in worlds without oxygen: Creation of an azotosome, Science Advances 1(1):e1400067.

S. Oleson (2014) Titan submarine: Exploring the depths of Kraken, NASA Glenn Research Center, Press release.

Cassini Solstice Mission, NASA Jet Propulsion Laboratory

NASA and ESA celebrate 10 years since Titan landing, NASA 2015

January 9, 2015December 23, 2015

How NASA Is Saving Fuel On Its Outer Solar System Missions

While Saturn is far away from us, scientists have just found a way to make the journey there easier. A new technique pinpointed the position of the ringed gas giant to within just two miles (four kilometers).

It’s an impressive technological feat that will improve spacecraft navigation and also help us better understand the orbits of the outer planets, the Jet Propulsion Laboratory (JPL) said.

It’s remarkable how much there is to learn about Saturn’s position given that the ancients discovered it, and it’s easily visible with the naked eye. That said, the new measurements with the Cassini spacecraft and the Very Long Baseline Array radio telescope array are 50 times more precise than previous measurements with telescopes on the ground.

“This work is a great step toward tying together our understanding of the orbits of the outer planets of our solar system and those of the inner planets,” stated study leader Dayton Jones of JPL.

Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute. Assembled by Gordan Ugarkovic. — Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute/Gordan Ugarkovic

What’s even more interesting is scientists have been using the better information as it comes in. Cassini began using the improved method in 2013 to improve its precision when it fires its engines.

This, in the long term, leads to fuel savings — allowing the spacecraft a better chance of surviving through the end of its latest mission extension, which currently is 2017. (It’s been orbiting Saturn since 2004.)

The technique is so successful that NASA plans to use the same method for the Juno spacecraft, which is en route to Jupiter for a 2016 arrival.

Juno will repeatedly dive between the planet and its intense belts of charged particle radiation, coming only 5,000 kilometers (about 3,000 miles) from the cloud tops at closest approach. (NASA/JPL-Caltech)

Scientists are excited about Cassini’s mission right now because it is allowing them to observe the planet and its moons as it reaches the summer solstice of its 29-year orbit.

This could, for example, provide information on how the climate of the moon Titan changes — particularly with regard to its atmosphere and ethane/methane-riddled seas, both believed to be huge influencers for the moon’s temperature.

Beyond the practical applications, the improved measurements of Saturn and Cassini’s position are also giving scientists more insight into Albert Einstein’s theory of general relatively, JPL stated. They are taking the same techniques and applying them to observing quasars — black-hole powered galaxies — when Saturn passes in front of them from the viewpoint of Earth.

Source: Jet Propulsion Laboratory