Posted on by Nancy Atkinson

What Happened During the Huygens Mission?

Artist depiction of Huygens landing on Titan. Credit: ESA

It was eight years ago on January 14, 2005 that the Huygens spacecraft descended through Titan’s murky atmosphere and touched down – if a bit precariously – by bouncing, sliding and wobbling across the surface of Saturn’s largest moon Titan. This was the first time a probe had touched down on an alien world in the outer Solar System.

But that surface wasn’t quite what we expected.

While earlier studies of data from Huygens determined the surface of Titan to be quite soft, scientists now think the surface consisted of a hard outer crust but is soft underneath, so that if an object put more pressure on the surface, it sank in significantly.

“It is like snow that has been frozen on top,” said Erich Karkoschka, a co-author of a paper published in October 2012. “If you walk carefully, you can walk as on a solid surface, but if you step on the snow a little too hard, you break in very deeply.”

The scientists think that Huygens landed in something similar to a flood plain on Earth, but that it was dry at the time. The analysis reveals that, on first contact with Titan’s surface, Huygens dug a hole 12 cm deep, before bouncing out onto a flat surface.

The probe, tilted by about 10 degrees in the direction of motion, then slid 30–40 cm across the surface.

A new animation. top of the event has been created using real data recorded by Huygen’s instruments, allowing us to witness this historical moment as if we had been there.

ESA explains:

The animation takes into account Titan’s atmospheric conditions, including the Sun and wind direction, the behaviour of the parachute (with some artistic interpretation only on the movement of the ropes after touchdown), and the dynamics of the landing itself.

Even the stones immediately facing Huygens were rendered to match the photograph of the landing site returned from the probe, which is revealed at the end of the animation.

Split into four sequences, the animation first shows a wide-angle view of the descent and landing followed by two close-ups of the touchdown from different angles, and finally a simulated view from Huygens itself – the true Huygens experience.

Also, a ‘fluffy’ dust-like material – most likely organic aerosols that are known to drizzle out of the Titan atmosphere – was thrown up and suspended for around four seconds around the probe following the impact. The dust was easily lifted, suggesting it was most likely dry and that there had not been any ‘rain’ of liquid ethane or methane for some time prior to the landing.

Huygens was released from the Cassini spacecraft on Christmas Day 2004, and arrived at Titan three weeks later. The probe began transmitting data to Cassini four minutes into its descent and continued to transmit data after landing at least as long as Cassini was above Titan’s horizon, for about 90 minutes, and radio telescopes on Earth continued to receive Huygen’s signal well past the expected lifetime of the craft.

Cassini was supposed to receive Huygen’s signal over two channels, but because of an operational commanding error, only one channel was used. This means that only 350 pictures were received instead of 700 that were expected. All Doppler radio measurements between Cassini and Huygens were lost as well; however, Doppler radio measurements of Huygens from Earth were made, though not as accurate as the expected measurements that Cassini would have made. But when added to accelerometer sensors on Huygens and VLBI tracking of the position of the Huygens probe from Earth, reasonably accurate wind speed and direction measurements could still be derived.

You can see images from the Huygens mission here.

Huygens is currently the most distant landing of any craft launched from Earth. Cassini has been in orbit around Saturn since July 2004, and will continue operations until 2017.

Sources: ESA, Wiki

Posted on by Nancy Atkinson

Chunks of Frozen Hydrocarbons May be Floating on Titan’s Lakes

This artist's concept envisions what hydrocarbon ice forming on a liquid hydrocarbon sea of Saturn's moon Titan might look like. Image credit: NASA/JPL-Caltech/USGS

The Cassini spacecraft has been getting some strange data from Saturn’s moon Titan, and scientists will soon test out whether there might be “icebergs” of sorts, blocks of hydrocarbon ice floating on the surface of the lakes and seas of liquid hydrocarbon.

“One of the most intriguing questions about these lakes and seas is whether they might host an exotic form of life,” said Jonathan Lunine, a paper co-author and Cassini interdisciplinary Titan scientist at Cornell University, Ithaca, N.Y. “And the formation of floating hydrocarbon ice will provide an opportunity for interesting chemistry along the boundary between liquid and solid, a boundary that may have been important in the origin of terrestrial life.”

Titan is the only other body besides Earth in our solar system with stable bodies of liquid on its surface. But it is too cold on Titan for water to be liquid, so hydrocarbons like ethane and methane fill lakebeds and seas there, and scientists have determined there is even a likely cycle of precipitation and evaporation that involves hydrocarbons.

Ethane and methane are organic molecules, which scientists think can be building blocks for the more complex chemistry from which life arose.

Cassini has seen a vast network of these hydrocarbon seas cover Titan’s northern hemisphere, while a more sporadic set of lakes are in the southern hemisphere.

It has long been thought that lakes or seas dotted Titan, ever since Voyager 1 and 2 flew past the Saturn system in the early 1980’s. But with Titan’s thick atmosphere, direct evidence was not obtained until 1995 during observations from the Hubble Space Telescope. The Cassini mission has imaged and mapped many of these bodies of liquids on Titan.

The Cassini spacecraft has been getting mixed readings in the reflectivity of the surfaces of lakes on Titan. A smooth surface or liquids dotted with chunks of ice could be a possibility explanation for the readings.

Up to this point, Cassini scientists assumed that Titan lakes would not have floating ice, because solid methane is denser than liquid methane and would sink. But a new model considers the interaction between the lakes and the atmosphere, resulting in different mixtures of compositions, pockets of nitrogen gas, and changes in temperature. The result, scientists found, is that winter ice will float in Titan’s methane-and-ethane-rich lakes and seas if the temperature is below the freezing point of methane — minus 297 degrees Fahrenheit (90.4 kelvins). The scientists realized all the varieties of ice they considered would float if they were composed of at least 5 percent “air,” which is an average composition for young sea ice on Earth. (“Air” on Titan has significantly more nitrogen than Earth air and almost no oxygen.)

If the temperature drops by just a few degrees, the ice will sink because of the relative proportions of nitrogen gas in the liquid versus the solid. Temperatures close to the freezing point of methane could lead to both floating and sinking ice – that is, a hydrocarbon ice crust above the liquid and blocks of hydrocarbon ice on the bottom of the lake bed. Scientists haven’t entirely figured out what color the ice would be, though they suspect it would be colorless, as it is on Earth, perhaps tinted reddish-brown from Titan’s atmosphere.

“We now know it’s possible to get methane-and-ethane-rich ice freezing over on Titan in thin blocks that congeal together as it gets colder — similar to what we see with Arctic sea ice at the onset of winter,” said Jason Hofgartner, first author on the paper and a Natural Sciences and Engineering Research Council of Canada scholar at Cornell. “We’ll want to take these conditions into consideration if we ever decide to explore the Titan surface some day.”

Cassini’s radar instrument will be able to test this model by watching what happens to the reflectivity of the surface of these lakes and seas. A hydrocarbon lake warming in the early spring thaw, as the northern lakes of Titan have begun to do, may become more reflective as ice rises to the surface. This would provide a rougher surface quality that reflects more radio energy back to Cassini, making it look brighter. As the weather turns warmer and the ice melts, the lake surface will be pure liquid, and will appear to the Cassini radar to darken.

“Cassini’s extended stay in the Saturn system gives us an unprecedented opportunity to watch the effects of seasonal change at Titan,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We’ll have an opportunity to see if the theories are right.”

Source: NASA/JPL

Posted on by Jason Major

Flying, Rolling Robot Might Make a Great Titan Explorer

The HyTAQ (Hybrid Terrestrial and Aerial Quadrotor) robot developed at Illinois Institute of Technology (IIT)

Ever since the Huygens probe landed on Titan back in January 2005, sending us our first tantalizing and oh-so-brief glimpses of the moon’s murky, pebbly surface, researchers have been dreaming up ways to explore further… after all, what’s more intriguing than a world in our own Solar System that’s basically a miniature version of an early Earth (even if it’s quite a few orders of magnitude chillier?)

Many concepts have been suggested as to the best way to explore Titan, from Mars-style rovers to boats that would sail its methane seas to powered gliders… and even hot-air balloons have been put on the table. Each of these have their own specific benefits, specially suited to the many environments that are found on Titan, but what if you could have two-in-one; what if you could, say, rove and fly?

That’s what this little robot can do.

Designed by Arash Kalantari and Matthew Spenko at the Robotics Lab at Illinois Institute of Technology, this rolling birdcage is actually a quadrotor flying craft that’s wrapped in a protective framework, allowing it to move freely along the ground and then take off when needed, maneuvering around obstacles easily.

A design like this, fitted with scientific instruments and given adequate power supply, might make a fantastic robotic explorer for Titan, where the atmosphere is thick and the terrain may range from rough and rocky to sandy and slushy. (And what safer way to ford a freezing-cold Titanic stream than fly over it?)

Also, the robot’s cage design may make it better suited to travel across the frozen crust of Titan’s flood plains, which have been found to have a consistency like damp sand with a layer of frozen snow on top. Where wheels could break through and get permanently stuck (a la Spirit) a rolling cage might remain on top. And if it does break through… well, fire up the engines and take off.

The robot (as it’s designed now) is also very energy-efficient, compared to quadrotors that only fly.

“During terrestrial locomotion, the robot only needs to overcome rolling resistance and consumes much less energy compared to the aerial mode,” the IIT website notes. “This solves one of the most vexing problems of quadrotors and rotorcraft in general — their short operation time. Experimental results show that the hybrid robot can travel a distance 4 times greater and operate almost 6 times longer than an aerial only system.”

Of course this is all just excited speculation at this point. No NASA or ESA contracts have been awarded to IIT to build the next Titan explorer, and who knows if the idea is on anyone else’s plate. But innovations like this, from schools and the private sector, are just the sorts of exciting things that set imaginations rolling (and flying!)

PIA08115_n

Color view of Titan’s surface, captured by the Huygens probe after landing in January 2005. (NASA/JPL/ESA/University of Arizona)

Video by RoboticsIIT

Posted on by Nancy Atkinson

Cry Me a Nile-Like River of Liquid Hydrocarbons on Titan

This image from NASA’s Cassini spacecraft shows a vast river system on Saturn’s moon Titan. It is the first time images from space have revealed a river system so vast and in such high resolution anywhere other than Earth. Image Credit: NASA/JPL-Caltech/ASI

Titan is appearing more Earth-like all the time (yes, a very cold, and early version of Earth), as now the Cassini spacecraft has spotted what appears to be a miniature extraterrestrial version of the Nile River: a river valley on Saturn’s moon Titan that extends from what looks like ‘headwaters’ out to a large sea. Not only is it a riverbed, but it appears to be filled with liquid; likely very cold hydrocarbons such as ethane or methane.


Scientists deduce that the river is filled with liquid because it appears dark along its entire extent in the high-resolution radar image, indicating a smooth surface.

It is the first time images have revealed a river system this vast and in such high resolution anywhere beyond Earth.

“Though there are some short, local meanders, the relative straightness of the river valley suggests it follows the trace of at least one fault, similar to other large rivers running into the southern margin of this same Titan sea,” says Jani Radebaugh, a Cassini radar team associate at Brigham Young University, USA. “Such faults – fractures in Titan’s bedrock – may not imply plate tectonics, like on Earth, but still lead to the opening of basins and perhaps to the formation of the giant seas themselves.”

While the Earthly Nile River is 6,650 kilometers (4,132 miles) long, Titan’s big river is about 400 km long.

Titan is the only other world we know of that has stable liquid on its surface. While Earth’s hydrologic cycle relies on water, Titan’s equivalent cycle involves hydrocarbons.

Images from Cassini’s visible-light cameras in late 2010 revealed regions that darkened after recent rainfall.

Cassini’s visual and infrared mapping spectrometer confirmed liquid ethane at a lake in Titan’s southern hemisphere known as Ontario Lacus in 2008.

“This radar-imaged river by Cassini provides another fantastic snapshot of a world in motion, which was first hinted at from the images of channels and gullies seen by ESA’s Huygens probe as it descended to the moon’s surface in 2005,” said Nicolas Altobelli, ESA’s Cassini Project Scientist.

See a full-sized image of Titan’s river here.

Source: ESA

Posted on by Jason Major

Titan’s Gravity Indicates a Thicker, Uneven Icy Crust

Color composite of Titan and Dione made from Cassini images acquired in May 2011. (NASA/JPL/SSI/J. Major)

It’s long been speculated that Saturn’s moon Titan may be harboring a global subsurface ocean below an icy crust, based on measurements of its rotation and orbit by NASA’s Cassini spacecraft. Titan exhibits a density and shape that indicates a pliable liquid internal layer — an underground ocean — possibly composed of water mixed with ammonia, a combination that would help explain the consistent amount of methane found in its thick atmosphere.

Now, further analysis of Cassini gravity measurements by a Stanford University team has shown that Titan’s ice layer is thicker and less uniform than originally estimated, indicating a more complex internal structure — and a stronger external influences for its heat.

Titan’s liquid subsurface ocean was previously estimated to be in the neighborhood of 100 km (62 miles) thick, sandwiched between a rocky core below and an icy shell above. This was based on the behavior of Titan in its orbit — or, more precisely, how Titan’s shape changes along the course of its orbit, as measured by Cassini’s radar instrument.

Because Titan’s 16-day orbit is not perfectly circular the moon experiences a stronger gravitational pull from Saturn at certain points than at others. As a result it’s flattened at the poles and constantly changing shape slightly — an effect called tidal flexing. Along with the decay of radioactive materials in its core, this flexing generates the internal heat that helps keep a subsurface ocean liquid.

A team of researchers from Stanford University, led by Howard Zebker, professor of geophysics and electrical engineering, used recent Cassini measurements of Titan’s topography and gravity to determine that the icy layer between the moon’s surface and ocean is up to twice as thick as previously thought — and it’s considerably thicker at the equator than at the poles.

“The picture of Titan that we get has an icy, rocky core with a radius of a little over 2,000 kilometers, an ocean somewhere in the range of 225 to 300 kilometers thick and an ice layer that is 200 kilometers thick,” said Zebker.

Different thicknesses of Titan’s ice layer would mean that there’s less heat being generated internally by the decay of radioactive materials in Titan’s core, because that type of heat would be more or less globally uniform. Instead, tidal flexing caused by the gravitational interactions with Saturn and neighboring smaller moons must play a stronger role in heating Titan’s insides.

Read more: Titan’s Tides Suggest a Subsurface Sea

With Cassini’s new measurements of Titan’s gravity, Zebker and his team calculated that the icy layer below Titan’s flattened poles is 3,000 meters (about 1.8 miles) thinner than average, while at the equator it’s 3,000 meters thicker than average. Combined with the moon’s surface features, this makes the average global thickness of the ice layer to be more like 200 km, not 100.

Heat generated by tidal flexing — which is more strongly felt at the poles — is thought to be the cause of the thinner ice there. Thinner ice would mean there’s more liquid water beneath the poles, which is denser and thus would exert a stronger gravitational pull… exactly what’s been found in Cassini’s measurements.

The findings were announced Tuesday, Dec. 4 at the AGU convention in San Francisco. Read more on the Stanford University news page.

Posted on by John Williams

A Colorful and Unexpected Reversal at Titan

This artist’s impression of Saturn’s moon Titan shows the change in observed atmospheric effects before, during and after equinox in 2009. The Titan globes also provide an impression of the detached haze layer that extends all around the moon (blue). This image was inspired by data from NASA’s Cassini mission. Image Credit: ESA

A certain slant, or shift, of light glinting off of Saturn’s moon Titan turns out to drive unexpected reversals in the moon’s atmosphere according to data from NASA’s Cassini spacecraft.

In a paper released in the November 28, 2012 issue of the journal Nature, scientists say in a press release that data from Cassini show evidence for sinking air where upwelling currents were seen earlier in the mission.

“Cassini’s up-close observations are likely the only ones we’ll have in our lifetime of a transition like this in action,” said Nick Teanby, the study’s lead author who is based at the University of Bristol, England, and is a Cassini team associate. “It’s extremely exciting to see such rapid changes on a body that usually changes so slowly and has a ‘year’ that is the equivalent of nearly 30 Earth years.”

Of the eight planets and dozens of moons in our solar system, just Earth, Venus, Mars and Titan have both a solid surface and a substantial atmosphere.

Cassini offers scientists a unique perspective during this change of seasons. The pole experiencing winter is typically pointed away from Earth because of its orbit around Saturn. Cassini provides scientists a platform to watch the atmosphere change over time and study the moon from angles impossible from Earth. It arrived at the ringed planet in 2004. Models of Titan’s atmosphere have predicted changes for two decades but Cassini is just now seeing new circulation patterns arise.

“Understanding Titan’s atmosphere gives us clues for understanding our own complex atmosphere,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Some of the complexity in both places arises from the interplay of atmospheric circulation and chemistry.”

While scientists recently have watched the formation of haze and a vortex over Titan’s south pole, other Cassini instruments, such as the composite infrared spectrometer (CIRS), have gathered data tied more to the circulation and chemistry of Titan’s orangish atmosphere especially at higher altitudes. The CIRS instrument also reveals subtle changes in vertical winds and global circulation. The instrument shows that atmospheric circulation extends about 100 km, or 60 miles, higher than expected. This is important in explaining the orangish tint to Titan’s atmosphere. A haze layer, first detected by Voyager 1, may be a region rich in small haze particles that combine to form larger aggregates that descend deep into the atmosphere giving the moon its characteristic color.

Scientists have narrowed down the atmospheric reversal to about six months near the August 2009 equinox when the Sun was shining directly on Titan’s equator.

“Next, we would expect to see the vortex over the south pole build up,” said Mike Flasar, the CIRS principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Md. “As that happens, one question is whether the south winter pole will be the identical twin of the north winter pole, or will it have a distinct personality? The most important thing is to be able to keep watching as these changes happen.”

Second image caption: This true color image captured by NASA’S Cassini spacecraft before a distant flyby of Saturn’s moon Titan on June 27, 2012, shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere. Image Credit: NASA/JPL-Caltech/Space Science Institute

Source: NASA/Jet Propulsion Laboratory

Posted on by John Williams

Swirling Vortex and Mini Moons: Spectacular Views of the Little Things Around Saturn

High-altitude clouds in Titan’s seasonal south polar swirl glow dimly in this image from NASA’s Cassini spacecraft.

With wild storms and a vast ring system, nothing seems small around Saturn. But as NASA’s Cassini spacecraft loops high over Saturn’s poles, scientists are taking time to explore the little things including a swirling vortex, the miniature moon Mimas, and another tiny ovoid moon named Methone.

Titan’s swirling vortex, lower right, glows brightly against the south polar clouds in this new image from NASA’s Cassini spacecraft. Scientists are monitoring the development of the swirling mass of gas to try and understand the weather related to the coming winter to the moon’s south pole. For a color closeup of the vortex, see Titan’s Colorful South Polar Vortex. If you’re more into a moving visualization, check out the vortex in motion.


Cassini acquired the view of the vortex on Titan on August 31, 2012 using a special filter sensitive to light in the near-infrared. Cassini took this image from a distance of about 1.2 million kilometers (750,000 miles) above the south pole of Titan. That’s nearly three times the distance between Earth and the Moon. The smallest detail on this image is about 4 miles across.

“Note the motions and beautifully detailed cloud patterns,” wrote Carolyn Porco, Cassini imaging team lead on the CICLOPS website, “very likely the result of open-cell convection — already visible in this fascinating phenomenon that we on Cassini have been fortunate to capture, for the first time, in the process of being born.”

Methone looks like a tiny gray egg in this image from NASA’s Cassini spacecraft.

Last week, the Cassini imaging team released two stunning images of Saturn. Tiny, egg-shaped Methone (pronounced meh-tho-nee) is barely 3 kilometers (2 miles) across. Cassini discovered this moon in 2004 hanging out between Mimas and Enceladus at just 194,000 km (120,000 miles) above Saturn. From Methone’s smooth surface, Saturn must be a true wonder. Small moons like Methone are generally non-round. Scientists believe they just don’t have the mass to pull themselves together into a round shape. The leading side of Methone is lit in this image and at a distance of just 4,000 km (2,500 miles) the smallest feature that can be seen is about 27 meters (88 feet).

Saturn’s moon Mimas is dwarfed by Saturn and its rings in this spectacular image from NASA’s Cassini spacecraft

Don’t blink or you might miss a tiny dot just to the upper left of Saturn. Mimas is dwarfed not only by Saturn’s rings, but also by the gigantic storms visible in the northern and southern hemisphere’s Mimas is just 396 km (246 miles) across and is the solar system’s 20th largest satellite. The moon could easily fit within the borders of Spain and most western states in the U.S. Cassini took this spectacular image from a distance of 2.4 million kilometers (1.5 million miles) from Saturn.

Source: NASA Jet Propulsion Laboratory and Cassini Imaging Central Laboratory for Operations (CICLOPS)

Posted on by Jason Major

Cassini Discovers Titan’s Glowing Atmosphere

A pair of images from NASA’s Cassini spacecraft show Titan glowing in the dark.

Titan never ceases to amaze. Saturn’s largest moon, it’s wrapped in a complex, multi-layered nitrogen-and-methane atmosphere ten times thicker than Earth’s. It has seasons and weather, as evidenced by the occasional formation of large bright clouds and, more recently, an area of open-cell convection forming over its south pole. Titan even boasts the distinction of being the only other world in the Solar System besides Earth with large amounts of liquid existing on its surface, although there in the form of exotic methane lakes and streams.

We have NASA’s Cassini spacecraft to thank for these discoveries, and now there’s one more for the ceaseless explorer to add to its list: Titan glows in the dark.

Seen above in two versions of the same calibrated raw image, acquired by Cassini on May 7, 2009, Titan hovers in front of a background field of stars which appear as blurred streaks due to the 560 seconds (about 9 1/2 minutes) exposure time and the relative motion of the spacecraft.

The image on the left shows Titan in visible light, receiving reflected sunlight off Saturn itself — “Saturnshine” — while the moon was on the ringed planet’s night side. The image on the right was processed to exclude this reflected light… and yet it still shines. (E pur si candeo?)

Read: Titan’s Surface “the Consistency of Soft, Damp Sand”

The hazy moon’s dim glow — measuring only around a millionth of a watt — comes from not only the top of its atmosphere (which was expected) but also from much deeper within, at altitudes of 300 km (190 miles).

The glow is created by chemical reactions within Titan’s atmosphere, sparked by interactions with charged particles from the Sun and Saturn’s magnetic field.

“It turns out that Titan glows in the dark – though very dimly,” said Robert West, the lead author of a recent study in the journal Geophysical Research Letters and a Cassini imaging team scientist at NASA’s Jet Propulsion Laboratory. “It’s a little like a neon sign, where electrons generated by electrical power bang into neon atoms and cause them to glow. Here we’re looking at light emitted when charged particles bang into nitrogen molecules in Titan’s atmosphere.”

The light is analogous to the airglow seen in Earth’s atmosphere, often photographed by astronauts aboard the ISS.

Still, even taking known sources of external radiation into account, Titan is glowing from within with an as-yet-unexplained light. More energetic cosmic rays may be to blame, penetrating deeper into the moon’s atmosphere, or there could be unexpected chemical reactions or phenomena at work — a little Titanic lightning, perhaps?

“This is exciting because we’ve never seen this at Titan before,” West said. “It tells us that we don’t know all there is to know about Titan and makes it even more mysterious.”

Read more on the Cassini mission page here, and see more images from Cassini on the CICLOPS imaging center site.

Images: NASA/JPL-Caltech/Space Science Institute. Inset image: Titan’s atmosphere and upper-level hydrocarbon haze, seen in June 2012. Color composite by J. Major.

Posted on by Nancy Atkinson

Titan’s Surface the “Consistency of Soft, Damp Sand”

Artist depiction of Huygens landing on Titan. Credit: ESA

Artist concept of the Huygens probe landing on the surface of Titan. Credit: ESA

Even though the Huygens probe landed on Titan back in 2005 and transmitted data for only about 90 minutes after touchdown, scientists are still able to eke information out about Titan from the mission, squeezing all they can from the data. The latest information comes from reconstructing the way the probe landed, and an international group of scientists say the probe “bounced, slid and wobbled” after touching down on Saturn’s moon, which provides insight into the nature of the Titan’s surface.

“A spike in the acceleration data suggests that during the first wobble, the probe likely encountered a pebble protruding by around 2 cm from the surface of Titan, and may have even pushed it into the ground, suggesting that the surface had a consistency of soft, damp sand,” describes Dr. Stefan Schröder of the Max Planck Institute for Solar System Research, lead author of a paper recently published in Planetary and Space Science.

An animation of the landing is below.

Schröder and his team were able to reconstruct the landing by analyzing data from different instruments that were active during the impact, and in particular they looked for changes in the acceleration experienced by the probe.

The instrument data were compared with results from computer simulations and a drop test using a model of Huygens designed to replicate the landing.

The scientists think that Huygens landed in something similar to a flood plain on Earth, but that it was dry at the time. The analysis reveals that, on first contact with Titan’s surface, Huygens dug a hole 12 cm deep, before bouncing out onto a flat surface.

The probe, tilted by about 10 degrees in the direction of motion, then slid 30–40 cm across the surface.

It slowed due to friction with the surface and, upon coming to its final resting place, wobbled back and forth five times. Motion subsided about 10 seconds after touchdown.

Earlier studies of data from Huygens determined the surface of Titan to be quite soft. The new study goes one step farther, the team said, to demonstrate that if something put little pressure on the surface, the surface was hard, but if an object put more pressure on the surface, it sank in significantly.

“It is like snow that has been frozen on top,” said Erich Karkoschka, a co-author at the University of Arizona, Tucson. “If you walk carefully, you can walk as on a solid surface, but if you step on the snow a little too hard, you break in very deeply.”

Had the probe impacted a wet, mud-like substance, its instruments would have recorded a “splat” with no further indication of bouncing or sliding. The surface must have therefore been soft enough to allow the probe to make a sizable depression, but hard enough to support Huygens rocking back and forth.

This raw image was returned by the Descent Imager/Spectral Radiometer camera onboard the European Space Agency’s Huygens probe after the probe descended through the atmosphere of Titan. It shows the surface of Titan with ice blocks strewn around. Credit: ESA/NASA/University of Arizona

“We also see in the Huygens landing data evidence of a ‘fluffy’ dust-like material – most likely organic aerosols that are known to drizzle out of the Titan atmosphere – being thrown up into the atmosphere and suspended there for around four seconds after the impact,” said Schröder.

Since the dust was easily lifted, it was most likely dry, suggesting that there had not been any rain of liquid ethane or methane for some time prior to the landing.

“You don’t get rain very often on Titan,” said Karkoschka, explaining that heavy downpours of liquid methane may occur decades or centuries apart. “When they do occur, they carve the channels we see in the pictures Huygens recorded as it approached the surface. The top layer at the landing site was completely dry, suggesting it hadn’t rained in a long time,” he added.

Karkoschka said that when Huygens landed, its downward-shining lamp warmed up the ground and caused methane to evaporate,” Karkoschka explained. “That tells us that just below the surface, the ground probably was wet.”

It has been suggested in earlier studies that the Huygens probe landed near the edge of one of Titan’s hydrocarbon lakes. Several hundred lakes and seas have been observed with the Cassini orbiter’s radar instruments, but with surface temperatures of minus 179 degrees Celsius (minus 290 degrees Fahrenheit), Titan does not have bodies of water. Instead, liquid hydrocarbons in the form of methane and ethane are present on the moon’s surface, with complex carbons making up dunes and other features on the surface.

Source: ESA

Posted on by Jason Major

Pictures From T-86: Cassini’s Latest Flyby of Titan

On September 26-27 Cassini executed its latest flyby of Titan, T-86, coming within 594 miles (956 km) of the cloud-covered moon in order to measure the effects of the Sun’s energy on its dense atmosphere and determine its variations at different altitudes.

The image above was captured as Cassini approached Titan from its night side, traveling about 13,000 mph (5.9 km/s). It’s a color-composite made from three separate raw images acquired in red, green and blue visible light filters.

Titan’s upper-level hydrocarbon haze is easily visible as a blue-green “shell” above its orange-colored clouds.

Cassini captured this image as it approached Titan’s sunlit limb, grabbing a better view of the upper haze. Some banding can be seen in its highest reaches.

The haze is the result of UV light from the Sun breaking down nitrogen and methane in Titan’s atmosphere, forming hydrocarbons that rise up and collect at altitudes of 300-400 kilometers. The sea-green coloration is a denser photochemical layer that extends upwards from about 200 km altitude.

In this image, made from data acquired on Sept. 27, Titan’s south polar vortex can be made out just within the southern terminator. The vortex is a relatively new feature in Titan’s atmosphere, first spotted earlier this year. It’s thought that it’s a region of open-cell convection forming above the moon’s pole, a result of the approach of winter to Titan’s southern half.

Read: Cassini Spots Surprising Swirls Above Titan’s South Pole

This T-86 flyby was was one of a handful of opportunities to profile Titan’s ionosphere from the outermost edge of Titan’s atmosphere. In addition Cassini was able to look for any changes to Ligeia Mare, a methane lake last observed in spring of 2007.

Now that Titan has been under scrutiny for a full year of Saturn’s seasons — which lasts 29.7 Earth-years — astronomers now know that varying amounts of solar radiation can drastically change situations both within Saturn’s atmosphere and on its surface.

“As with Earth, conditions on Titan change with its seasons. We can see differences in atmospheric temperatures, chemical composition and circulation patterns, especially at the poles,” said Dr. Athena Coustenis from the Paris-Meudon Observatory in France. “For example, hydrocarbon lakes form around the north polar region during winter due to colder temperatures and condensation. Also, a haze layer surrounding Titan at the northern pole is significantly reduced during the equinox because of the atmospheric circulation patterns. This is all very surprising because we didn’t expect to find any such rapid changes, especially in the deeper layers of the atmosphere.”

“It’s amazing to think that the Sun still dominates over other energy sources even as far out as Titan, over 1.5 billion kilometres from us.”
– Dr. Athena Coustenis, Paris-Meudon Observatory

The image above, acquired on Sept. 28, was added to this post on Oct. 1. It was taken from a distance of  649,825 miles (1,045,792 kilometers.)

Cassini’s next targeted approach to Titan — T-87 — will occur on November 13.

Get more news from the Cassini mission here.

Image credits: NASA/JPL/Space Science Institute. All color composites by Jason Major. Images have not been validated or calibrated by the SSI team.

 

(Do you love the Cassini mission as much as we do? Vote on your favorite Cassini “Shining Moment” here, in honor of the 15th anniversary of Cassini’s launch on October 15! Amazing to think it’s already been 15 years — 8 of those in orbit around Saturn!)