Cassini Archives

November 5, 2012December 23, 2015 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.

October 25, 2012December 23, 2015 by Nancy Atkinson

Giant “Invisible” Vortex Still Remains on Saturn Following Huge Storm

In 2010, a small, bright white storm emerged on Saturn’s northern hemisphere. This storm grew until it wrapped around the planet in curly cloud structures, creating a colossal atmospheric disturbance that endured into the early part of 2012, becoming the largest storm seen on the planet since 1990. Being in orbit around the ringed planet, the Cassini spacecraft had a front row seat to watch the disturbance unfold, allowing planetary scientists an unprecedented look at this monster storm. While the storm was visible even to amateur astronomers on Earth, much of its activity took place beyond the reach of visible-light cameras and telescopes, astronomers say. Not only did huge “beacons” of hot air chase each other around the planet, but infrared observations show a giant oval vortex is still persisting as a side effect from the storm.

“It’s the first time we’ve seen anything like it on any planet in the Solar System,” said Leigh Fletcher from the University of Oxford, UK, lead author of a paper describing the unprecedented storm. “It’s extremely unusual, as we can only see the vortex at infrared wavelengths – we can’t tell that it is there simply by looking at the cloud cover.”

Fletcher and her team also used ground-based observations with the Very Large Telescope of the European Southern Observatory in Chile, and NASA’s Infrared Telescope Facility at the summit of Mauna Kea in Hawaii.

As the visible storm erupted in the roiling cloud deck of Saturn’s troposphere, waves of energy rippled hundreds of kilometers upwards, depositing their energy as the two vast ‘beacons’ of hot air in the stratosphere.

Data from Cassini’s composite infrared spectrometer (CIRS) instrument revealed the storm’s powerful discharge sent the temperature in Saturn’s stratosphere soaring 65 degrees C (150 degrees Fahrenheit, 83 kelvins) above normal.

Researchers described in a complimentary paper that will be published in the Nov. 20 issue of the Astrophysical Journal this as a “belch” of energy, as they observed a huge increase in the amount of ethylene gas in Saturn’s atmosphere, the origin of which is a mystery. Ethylene, an odorless, colorless gas, isn’t typically observed on Saturn. On Earth, it is created by natural and man-made sources.

Researchers are still is exploring the origin of the ethylene, but they have ruled out a large reservoir deep in the atmosphere.

“We’ve really never been able to see ethylene on Saturn before, so this was a complete surprise,” said Goddard’s Michael Flasar, the CIRS team lead.

The beacons were expected to cool down and dissipate, but by late April 2011 – by which time bright cloud material had encircled the entire planet – the hot spots had merged to create an enormous vortex that for a brief period exceeded even the size of Jupiter’s famous Great Red Spot.

The forceful storm generated unprecedented spikes in temperature and increased amounts of ethylene. In these two sets of measurements taken by Cassini’s composite infrared spectrometer, yellow represents the highest temperatures. Each strip maps a single molecule (top: methane, bottom: ethylene), with temperature measurements taken in the northern hemisphere, all the way around the planet. Image credit: NASA/JPL-Caltech/GSFC

Although comparisons to Jupiter’s Red Spot have been made to this storm, Saturn’s storm was much higher in the atmosphere while Jupiter’s vortex is embedded deep down in the turbulent ‘weather zone’, Fletcher said.

Also, Jupiter’s famous vortex has raged for at least 300 years. But after traversing the planet once every 120 days since May 2011, Saturn’s large beacon is cooling and shrinking. Scientists expect it to fade away completely by the end of 2013.

The question now remains as to whether Saturn’s storm-generating energy has been sapped or if there will be a repeat performance, the team said.

The outburst already caught observers by surprise by arriving during the planet’s northern hemisphere spring, years ahead of the predictably stormy summer season.

“The beauty is that Cassini will be operating until the Saturn system reaches its summer solstice in 2017, so if there is another global event like this, we’ll be there to see it,” says ESA’s Cassini project scientist Nicolas Altobelli.

Sources: JPL, ESA, NASA

October 16, 2012December 23, 2015 by Nancy Atkinson

Timeline: 15 Years of Cassini

The Cassini spacecraft takes an angled view toward Saturn, showing the southern reaches of the planet with the rings on a dramatic diagonal. Credit: NASA/JPL-Caltech/Space Science Institute

The Cassini mission has been a source of awe-inspiring images, surprising science and incredible longevity. Since launching on Oct. 15, 1997, the Cassini spacecraft has logged more than 6.1 billion kilometers (3.8 billion miles)of exploration – enough to circle Earth more than 152,000 times. After flying by Venus twice, Earth, and then Jupiter on its way to Saturn, Cassini pulled into orbit around the ringed planet in 2004 and has been spending its last eight years weaving around Saturn, its glittering rings and intriguing moons.

The spacecraft has sent back some 444 gigabytes of scientific data so far, including more than 300,000 images. More than 2,500 reports have been published in scientific journals based on Cassini data, describing the discovery of the plume of water ice and organic particles spewing from the moon Enceladus; the first views of the hydrocarbon-filled lakes of Saturn’s largest moon Titan; the atmospheric upheaval from a rare, monstrous storm on Saturn and many other curious phenomena.

The folks from the Cassini mission have put together a great infographic that provides a timeline of Cassini’s mission and some of its “greatest hits” — major events and discoveries. See below:

October 12, 2012December 23, 2015 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

September 30, 2012December 23, 2015 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!)

September 21, 2012December 23, 2015 by Jason Major

Saturn Shows Off Its Shadow

Take a look up at the enormous shadow cast by Saturn onto its own rings in this raw image, acquired by NASA’s Cassini spacecraft on September 18, 2012.

Cassini captured this image from below Saturn’s ring plane at a distance of 1,393,386 miles (2,242,437 kilometers). It shows not only the gas giant’s shadow but also the wispy nature of the rings, which, although complex, extensive and highly reflective (the light seen on Saturn above is reflected light from the rings!) they are still very thin — less than a mile (about 1 km) on average and in some places as little as thirty feet (10 meters) thick.

Seen in the right light, some of the thin innermost rings can seem to nearly disappear entirely — especially when backlit by Saturn itself.

Views like the one above are once again possible because of Cassini’s new orbit, which takes it high above and below the ring plane, providing a new perspective for studying Saturn and its moons. Ultimately by next April the spacecraft will be orbiting Saturn at an inclination of about 62 degrees — that’d be like an orbit around Earth that goes from Alaska to the northernmost tip of Antarctica. (Find out how Cassini alters its orbit here.)

With this viewpoint Cassini will get some great views of Saturn’s north and south poles, which are gradually moving into their summer and winter seasons, respectively, during the ringed planet’s 29.5-Earth-year orbital period.

After more than 8 years in orbit Cassini is still fascinating us with enthralling images of Saturn on a regular basis. Read more about the Cassini mission here.

Cassini spots shepherd moons Pan (within the Encke Gap) and Prometheus (along the inner edge of the F ring) in an image acquired on Sept. 18, 2012

Images: NASA/JPL/Space Science Institute.

August 30, 2012December 23, 2015 by John Williams

Changing Hues Signal Transition of Seasons at Saturn

The giant moon Titan passes in front of Saturn in this natural-color, wide-angle view from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

[SPOILER ALERT: Viewing these images will force you to change your computer wallpaper]

Here on Earth, it’s almost time for the burst of fall color that signals the change of seasons in the Northern Hemisphere. Saturn’s color too is transforming subtly as the gas giant slips into a Saturnian spring and autumn as seen in this series of true-color images from NASA’s Cassini spacecraft.

Titan, a moon larger than the planet Mercury, hangs before the rings and changing colors of Saturn in the first of four spectacular images release by NASA and the Cassini Imaging Central Laboratory for Operations (CICLOPS).

“For no other reason than that they are gorgeous, the Cassini imaging team is releasing today a set of fabulous images of Saturn and Titan…in living color…for your day-dreaming enjoyment,” said Carolyn Porco, Cassini imaging team lead based at the Space Science Institute in Boulder, Colordo, in an email blast.

When Cassini arrived at Saturn eight years ago, the planet’s northern hemisphere, locked in winter, showed azure blue. Now as winter passes to the southern hemisphere, the colors are reversing as the blue fades from the north and rises in the south.

“Note that our presence at Saturn for the last eight years has made possible the sighting of subtle changes with time, and one such change is obvious here,” Porco said. “As the seasons have advanced, and spring has come to the north and autumn to the south throughout the Saturn system, the azure blue in the northern winter Saturnian hemisphere that greeted Cassini upon its arrival in 2004 is now fading; and it is now the southern hemisphere, in its approach to winter, that is taking on a bluish hue.”

Scientists believe that the increasing blue color in the south likely is due to the increasing intensity of ultraviolet light from the Sun which produces the haze. Methane in the atmosphere also absorbs light toward the red end of the spectrum while reflecting blue light. This view looks from just above the ring plane with the Sun shining from above casting broad shadows on the colorful clouds of Saturn. The image was taken on May 6, 2012 from about 778,000 kilometers (483,000 miles) from Titan.

Some of the views, including this image of a vortex at Titan’s south pole are only possible because of a newly tilted, or inclined, orbit that takes Cassini high over the poles of Saturn and its moons. Scientists first noticed the detached mass of clouds over the south pole in March. The swirling mass of the vortex stands out clearly against the golden cloud deck surrounding Titan.

The recently formed south polar vortex stands out against Titan in this natural-color view from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

Sunlight scattering through Titan’s atmosphere forms a ring of color as NASA’s Cassini spacecraft cruises along the night side of Saturn’s largest moon. Image Credit: NASA/JPL-Caltech/SSI

A glowing hint of the polar vortex shows in this image looking toward the night-time, Saturn-facing side of Titan. Sunlight scattering through Titan’s atmosphere forms the ring of color in this image taken about 216,000 kilometers (134,000 miles) from Titan.

Saturn’s rings cut colorful Titan in half in this image from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

The rings obscure Titan in the final image of the quartet. The image is taken from just above the northern, sunlit side of the ring plane. Saturn’s shadow cast along the rings create the dark swath in the center of the image but if you look close, you can see a tiny sliver of Titan through the Cassini Division, the largest gap in Saturn’s wide rings.

“Cassini has been in orbit now for the last eight years, and despite the fact that we can’t know exactly what the next five years will show us, we can be certain that whatever it is will be wondrous,” said Porco.

About the author: John Williams is owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

August 20, 2012December 23, 2015 by John Williams

Look at the Size of that Thing! – A Close Look at Odysseus Crater

Credit: NASA/JPL/Space Science Institute

Behold the battered terrain of the massive crater Odysseus in this new image from Cassini.

Check out the cassinified image of the fractured surface

When Voyager first imaged the huge Herschel Crater on Mimas, scientists could not help comparing the small and battered moon to the Death Star in George Lucas’ science-fiction adventure Star Wars. But Saturn’s moon Tethys is also home to a massive crater; the remains of an ancient impact that nearly destroyed the tiny moon. Odysseus Crater dominates the surface of Tethys covering two-thirds of the surface. The tiny moon is just 1062 kilometers, or 660 miles, across. Using information from Voyager and Cassini, scientists found that the heavily cratered and fractured moon is made up of mostly water ice with a small amount of rock.

Odysseus Crater takes up the entire left side of this image.

With the Sun over Cassini’s shoulder, the spacecraft took this image of the northern part of Odysseus June 28, 2012 while the spacecraft zipped along just 72,000 kilometers (45,000 miles) above Tethys. If you’re interested, the resolution of this image is about 430 meters (1,409 feet) per pixel; meaning that one pixel takes up 430 meters in the image.

John Williams is a science writer and owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

August 15, 2012December 23, 2015 by John Williams

Treasure Hunt for Cassini Reveals Tiny Moon Atlas

Saturn's tiny moon Atlas shines with the rings

Saturn’s tiny moon Atlas shines with the rings

While most eyes on Earth have been focused on the Red Planet and the eventful landing of the Curiosity Rover, other missions throughout the Solar System are delivering stunning vistas as well, such as this image from NASA’s Cassini spacecraft of tiny moon Atlas as it shines just above Saturn’s rings.

Can you find it?

Atlas, just 30 kilometers (or 19 miles) across, sits just above the ring plane in this image taken by Cassini’s narrow-angle camera on April 16, 2012 at a distance of 1.4 million kilometers (870,000 miles). At this distance, Atlas appears as a small white dot. Atlas orbits Saturn between the main rings and the thin F ring.

Cassini arrived at Saturn in 2004 and is now in its second extended mission called Cassini Solstice Mission. For the past two years, Cassini cruised in an equatorial orbit flying close over several moons including Titan and studying the planet’s iconic rings. Over the next three years, Cassini will hurtle high above the poles, sending the probe through the ring plane many times.

July 26, 2012December 23, 2015 by Jenny Winder

Beneath the Mask, Titan looks Surprisingly Smooth and Youthful

Images from the Cassini mission show river networks draining into lakes in Titans north polar region. Credit: NASA/JPL/USGS.

Caption: Images from the Cassini mission show methane river networks draining into lakes in Titan’s north polar region. Credit: NASA/JPL/USG

Saturn’s largest moon, Titan has long been hidden beneath the thick shroud of its methane- and nitrogen-rich atmosphere. That all changed in 2004 when NASA’s Cassini mission was able to penetrate the haze and sent back detailed radar images of the surface. These showed an icy terrain, carved over millions of years, by rivers similar to those found here on Earth. However, Titan’s surface doesn’t look as old and weather-beaten as it should. The rivers have caused surprisingly little erosion and there are fewer impact craters than would be expected. So what is the secret to Titan’s youthful complexion?

Titan is around four billion years old, roughly the same age as the rest of the solar system. But the low number of impact craters put estimates of its surface at only between 100 million and one billion years old.

Researchers at MIT and the University of Tennessee at Knoxville have analyzed images of Titan’s river networks and suggest two possible explanations: either erosion on Titan is extremely slow, or some recent phenomena has wiped out older surface features.

Taylor Perron, the Cecil and Ida Green Assistant Professor of Geology at MIT explains, “It’s a surface that should have eroded much more than what we’re seeing, if the river networks have been active for a long time. It raises some very interesting questions about what has been happening on Titan in the last billion years.”

Perron suggests that geological processes on Titan may be like those we see here on Earth. Here too, impact craters are scarce, as plate tectonics, erupting volcanoes, advancing glaciers and river networks reshaped our planet’s surface over billions of years, so, on Titan, tectonic upheaval, cryovolcanic eruptions, erosion and sedimentation by rivers could be altering the surface.

Discovering which processes are at work is not easy. The images from Cassini are like aerial photos but with much coarser resolution. They are flat, with no information about a surface elevation or depth.

Perron and MIT graduate student Benjamin Black analyzed the images and mapped 52 prominent river networks from four regions on Titan. They then compared the images with a model of river network evolution developed by Perron. Their data depicts the evolution of a river over time, taking into account variables such as the strength of the underlying material and the rate of flow through the river channels. As a river erodes, it transforms from a long, spindly thread into a dense, treelike network of tributaries. Titan’s river networks have maintained their long and spindly composition. They compare with recently renewed landscapes here including volcanic terrain on the island of Kauai and recently glaciated landscapes in North America.

Besides Earth, Titan is the only world with an active hydrologic cycle forming active river networks. Titan’s surface temperature may be about 94 K and its rivers run with liquid methane but as Perron says “It’s a weirdly Earth-like place, even with this exotic combination of materials and temperatures, and so you can still say something definitive about the erosion. It’s the same physics.”

Below is a video of Black and Perron explaining their research:

Find out more