NASA Cassini Sails into New Ocean Adventures on Titan

Cassini radar data reveal the depth of a liquid methane/ethane sea on Saturn's moon Titan near the mouth of a large, flooded river valley.

Image Credit: NASA/JPL-Caltech/ASI/Cornell

Cassini's radar instrument images show that a bright feature appeared in Kraken Mare, Titan's largest sea.

Image Credit: NASA/JPL-Caltech/ASI/Cornell

NASA's Cassini mission continues its adventures in extraterrestrial oceanography with new findings about the hydrocarbon seas on Saturn's moon Titan.

During a flyby in August, the spacecraft sounded the depths near the mouth of a flooded river valley and observed new, bright features in the seas that might be related to the mysterious feature that researchers dubbed the "magic island."

The findings are being presented this week at the Division for Planetary Sciences Meeting of the American Astronomical Society held in Tucson, Arizona.

To the delight of Cassini scientists, two new bright features appeared in Titan’s largest sea, Kraken Mare, during the August 21 flyby.

In contrast to a previously reported bright, mystery feature in another of Titan's large seas, Ligeia Mare, the new features in Kraken Mare were observed in both radar data and images from Cassini's Visible and Infrared Mapping Spectrometer (VIMS).

Having observations at two different wavelengths provides researchers with important clues to the nature of these enigmatic objects.

The VIMS data suggest the new features might have similarities to places in and around the seas that the Cassini team has interpreted as waves or wet ground.

The observations support two of the possible explanations the team thinks are most likely, that the features might be waves or floating debris.

Unfortunately for mystery lovers, the August Titan flyby marked the final opportunity for Cassini's radar to observe Kraken Mare.

However, the spacecraft is scheduled to observe the original "magic island" feature in Ligeia Mare once more, in January 2015.

The August Titan flyby also included a segment designed to collect altimetry (or height) data, using the spacecraft's radar instrument along a 120-mile (200-kilometer) shore-to-shore track of Kraken Mare.

For a 25-mile (40-kilometer) segment of this data along the sea's eastern shoreline, Cassini's radar beam bounced off the sea bottom and back to the spacecraft, revealing the sea's depth in that area.

This region, which is near the mouth of a large, flooded river valley, showed depths of 66 to 115 feet (20 to 35 meters).

Cassini will perform this experiment one last time in January 2015, to try to measure the depth of Punga Mare.

Punga Mare is the smallest of three large seas in Titan's far north, and the only sea whose depth has not been observed by Cassini.

Scientists think that, for the areas in which Cassini did not observe a radar echo from the seafloor, Kraken Mare might be too deep for the radar beam to penetrate.

Alternatively, the signal over this region might simply have been absorbed by the liquid, which is mostly methane and ethane.

The altimetry data for the area in and around Kraken Mare also showed relatively steep slopes leading down to the sea, which also suggests the Kraken Mare might indeed be quite deep.

NASA Cassini sunny Hydrocarbon seas on Titan

This near-infrared, colour mosaic from NASA's Cassini spacecraft shows the sun glinting off of Titan's north polar seas.

While Cassini has captured, separately, views of the polar seas and the sun glinting off of them in the past, this is the first time both have been seen together in the same view.

The sunglint, also called a specular reflection, is the bright area near the 11 o'clock position at upper left.

This mirror-like reflection, known as the specular point, is in the south of Titan's largest sea, Kraken Mare, just north of an island archipelago separating two separate parts of the sea.

This particular sunglint was so bright as to saturate the detector of Cassini's Visual and Infrared Mapping Spectrometer (VIMS) instrument, which captures the view.

It is also the sunglint seen with the highest observation elevation so far, the sun was a full 40 degrees above the horizon as seen from Kraken Mare at this time, much higher than the 22 degrees seen in PIA18433.

Because it was so bright, this glint was visible through the haze at much lower wavelengths than before, down to 1.3 microns.

The southern portion of Kraken Mare (the area surrounding the specular feature toward upper left) displays a "bathtub ring," a bright margin of evaporate deposits, which indicates that the sea was larger at some point in the past and has become smaller due to evaporation.

The deposits are material left behind after the methane & ethane liquid evaporates, somewhat akin to the saline crust on a salt flat.

The highest resolution data from this flyby, the area seen immediately to the right of the sunglint, cover the labyrinth of channels that connect Kraken Mare to another large sea, Ligeia Mare.

Ligeia Mare itself is partially covered in its northern reaches by a bright, arrow-shaped complex of clouds.

The clouds are made of liquid methane droplets, and could be actively refilling the lakes with rainfall.

The view was acquired during Cassini's August 21, 2014, flyby of Titan, also referred to as "T104" by the Cassini team.

The view contains real colour information, although it is not the natural color the human eye would see.

Here, red in the image corresponds to 5.0 microns, green to 2.0 microns, and blue to 1.3 microns.

These wavelengths correspond to atmospheric windows through which Titan's surface is visible. The unaided human eye would see nothing but haze.

Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho

Cassini captures evolution of mysterious feature in Titan sea - Video

These three images, created from Cassini Synthetic Aperture Radar (SAR) data, show the appearance and evolution of a mysterious feature in Ligeia Mare, one of the largest hydrocarbon seas on Saturn's moon Titan. 

Credit: NASA/JPL-Caltech/ASI/Cornell



NASA's Cassini spacecraft is monitoring the evolution of a mysterious feature in a large hydrocarbon sea on Saturn's moon Titan.

The feature covers an area of about 100 square miles (260 square kilometers) in Ligeia Mare, one of the largest seas on Titan.

It has now been observed twice by Cassinis radar experiment, but its appearance changed between the two apparitions.

The mysterious feature, which appears bright in radar images against the dark background of the liquid sea, was first spotted during Cassini's July 2013 Titan flyby.

Ligeia Mare on Titan. 

Credit: NASA Cassini

Previous observations showed no sign of bright features in that part of Ligeia Mare.

Scientists were perplexed to find the feature had vanished when they looked again, over several months, with low-resolution radar and Cassini's infrared imager (VIMS).

This led some team members to suggest it might have been a transient feature, but during Cassini's flyby on August 21, 2014, the feature was again visible, and its appearance had changed during the 11 months since it was last seen.

Scientists on the radar team are confident that the feature is not an artifact, or flaw, in their data, which would have been one of the simplest explanations.

They also do not see evidence that its appearance results from evaporation in the sea, as the overall shoreline of Ligeia Mare has not changed noticeably.

The team has suggested the feature could be surface waves, rising bubbles, floating solids, solids suspended just below the surface, or perhaps something more exotic.

The researchers suspect that the appearance of this feature could be related to changing seasons on Titan, as summer draws near in the moon's northern hemisphere.

Monitoring such changes is a major goal for Cassini's current extended mission.

"Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan," said Stephen Wall, the deputy team lead of Cassini's radar team, based at NASA's Jet Propulsion Laboratory in Pasadena, California.

"We're hopeful that we'll be able to continue watching the changes unfold and gain insights about what's going on in that alien sea."

More information: Images of the feature taken during the Cassini flybys are available at: photojournal.jpl.nasa.gov/catalog/PIA18430

NASA Cassini: Hydrocarbon Clouds Move On Saturn's Huge Moon Titan

Clouds cruise through the skies of Saturn's largest moon, Titan, in striking new imagery captured by NASA's Cassini spacecraft.

In a rare sight for scientists, Cassini captured views of methane clouds drifting across Ligeia Mare, a big hydrocarbon sea near Titan's north pole, from July 20 through July 22.

Few clouds had been seen on Titan since the dissipation of a major storm in 2010, so researchers are trying to gauge the significance of the new observations.

"We're eager to find out if the clouds' appearance signals the beginning of summer weather patterns, or if it is an isolated occurrence," Cassini imaging team associate Elizabeth Turtle, of the Johns Hopkins University Applied Physics Lab in Laurel, Maryland, said in a statement.

"Also, how are the clouds related to the seas? Did Cassini just happen catch them over the seas, or do they form there preferentially?"

NASA's Cassini spacecraft viewed renewed cloud activity in Titan's northern polar region. Image taken on July 21, 2014. 

Credit: NASA /JPL-Caltech /Space Science Institute

The clouds' motion suggests wind speeds of about 7 to 10 mph (11 to 16 km/h), researchers said.

Saturn and its many moons take 30 years to complete one lap around the sun, so seasons in the Saturn system each last a little more than seven years.

It is now summer in Titan's northern hemisphere; the moon's summer solstice, which marks the midpoint of the season, comes in 2017. Titan, at 3,200 miles (5,150 kilometers) across, is about 50 percent larger than Earth's moon.

Modeling work had suggested that cloud formation should have increased in Titan's northern regions as summer took hold and temperatures rose, but such predictions have not been borne out to date, researchers said.

Titan is the only body in the solar system besides Earth known to possess stable bodies of liquid on its surface. Unlike Earth, however, Titan's climate system is hydrocarbon-based, with methane rain flowing into seas and lakes on the frigid moon's surface.

The $3.2 billion Cassini mission launched in 1997 and began orbiting Saturn in 2004, at the height of the gas giant's northern winter.

Cassini's long life is allowing researchers to track seasonal changes in the Saturn system; the probe is currently scheduled to operate through September 2017, when it will make an intentional death plunge into the ringed planet's thick atmosphere.

That final, fatal maneuver will ensure that Cassini does not contaminate Titan or Enceladus, two Saturn moons that may be capable of supporting life.

Cassini imaged the Titan clouds last month as it sped away from the satellite after a close flyby. Another encounter with Titan is planned for Aug. 21.

NASA Cassini Probe Celebrates 10 Years orbiting Saturn - Video

A photo taken of Saturn by the Cassini spacecraft, which has been exploring the Saturn system for 10 years. Image uploaded June 30, 2014.

Credit: NASA/JPL

NASA spacecraft Cassini passes a big milestone, a decade exploring Saturn and its many moons.

Since arriving in orbit around Saturn 10 years ago today, the Cassini probe has made a number of unprecedented observations and discoveries.

Although the spacecraft was originally approved for a four-year mission, it has been granted three mission extensions, allowing it to continue roaming the gas giant’s system.

Linda Spilker

"Having a healthy, long-lived spacecraft at Saturn has afforded us a precious opportunity," Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a statement.

"By having a decade there with Cassini, we have been privileged to witness never-before-seen events that are changing our understanding of how planetary systems form and what conditions might lead to habitats for life."

For example, Cassini has helped scientists learn more about what kinds of molecules populate our solar system.

The spacecraft discovered plumes containing water-ice shooting out into space from the south polar region of Saturn’s moon Enceladus.



The Enceladus discovery is one of Cassini’s most remarkable findings because it marked an extension of the search for life in the solar system, NASA officials said.

Researchers know that life as we understand it relies on water, so finding the substance on a moon or planet could be a sign that life might be able to exist there.

Scientists now think that Enceldus harbors an underground ocean.

Enceladus wasn’t the only mysterious moon Cassini helped reveal. Saturn’s huge satellite Titan has also been studied by the long-lasting orbiter.

Cassini’s measurements have shown that Titan has rain, lakes, seas and rivers like Earth, NASA officials said. Unlike Earth, however, Titan is a cold world with seas of liquid methane rather than water.

The Titan-exploring Huygens probe also launched to the Saturn system with Cassini in October 1997.

The European Space Agency’s Huygens robot landed on Titan in 2005 and became the first manmade craft to land on a moon in the outer solar system.

It measured the atmosphere and beamed images of the moon back to Earth.

“The probe’s 2 hour and 27 minute descent revealed Titan to be remarkably like Earth before life evolved, with methane rain, erosion and drainage channels and dry lake beds,” NASA officials said.

“A soup of complex hydrocarbons, including benzene, was found in Titan's atmosphere.”

Saturn's moon Tethys with its prominent Odysseus Crater silently slips behind Saturn's largest moon Titan.

Cassini has also unveiled how Saturn’s rings change over time, and because of its long tenure in the planetary system, the probe has observed seasonal changes taking place on the planet and its moons, according to NASA.

Cassini will continue to beam back data to Earth for a few more years, until 2017 when it is scheduled to intentionally plunge into Saturn’s atmosphere, ending its mission.

Hydrocarbon Lakes on Titan

Titan: Clue to 'Magic Island' mystery on Saturn moon

The bright feature shown in the image was spotted in images from July last year, but a few days later it had vanished

Scientists have outlined their best explanations for a mysterious feature dubbed the "magic island", which has been spotted on Saturn's moon Titan.

The Cassini spacecraft captured the "island" during a flyby, but it had vanished by the time of the next pass.

The bright splodge is seen in Ligeia Mare, one of the seas of methane and ethane found at Titan's north pole.

Icebergs, waves and gas bubbling up from the sea bed are all possibilities, the scientists say.

The study by an international team has been published in the journal Nature Geoscience.

Ligeia Mare is the second largest body of liquid on the saturnian moon

Saturn's largest moon shares much in common with Earth, such as a substantial atmosphere and a seasonal cycle. Wind and rain shape the surface to form river channels, seas, dunes and shorelines.

Titan's mountains and dune fields are made of ice, rather than rock or sand, and liquid hydrocarbons take many of the roles played by water on Earth.

The seas and lakes peppering the moon's north polar region are filled with methane and ethane. These are gases on Earth, but at typical Titan temperatures of -180C, they exist in a liquid state.

Titan, seen here with Tethys in the background, is shrouded in an orange haze of organic chemicals

• Titan is Saturn's largest moon and the second biggest in the Solar System
• It is the only moon in the Solar System with clouds and a substantial atmosphere
• Wind and rain create similar features to those found on Earth, such as dunes, lakes and rivers
• But on Titan it rains liquid methane, filling the rivers, lakes and seas with hydrocarbons

The bright feature was spotted in pictures from a Cassini flyby of Titan on 10 July 2013. The "island" is absent in imagery of Ligeia Mare taken on three previous flybys.

By the time of the next pass of Titan, on 26 July, the feature had vanished, and was not visible in two subsequent flybys.

"'Magic island' is a colloquial term that we use within the team to refer to this. But we don't actually think it's an island," co-author Jason Hofgartner told reporters.

The feature appears and disappears too quickly to be a volcanic islet. So the team were left with a handful of potential explanations.

Titan's lakes and seas are thought to be filled with a mixture of liquid methane and ethane

Mr Hofgartner, who is based at Cornell University in New York, explained: "We have four different hypotheses that are all equally preferred. In no particular order they are: waves, rising bubbles, floating solids and suspended solids."

Titan operates on a 30-year seasonal cycle, and the moon's northern region is expected to become a more dynamic place as Titan approaches its summer solstice in May 2017.

"Right now, Titan is basically half way between the vernal equinox (August 2009) - at the beginning of spring - and the summer solstice, the start of summer. It's roughly equivalent to what we would consider the beginning of May," said Mr Hofgartner.

"As Titan approaches its summer, more of the Sun's energy is being deposited in the northern hemisphere."

Winds will get stronger, causing an increase in waves, which are one potential explanation for the "magic island". Researchers have already seen possible evidence for small waves on another Titan sea.

NASA Cassini Titan flyby: Data collected on mysterious hydrocarbon lakes

Credit: NASA/JPL-Caltech /University of Arizona /University of Idaho

NASA's Cassini mission flew past Titan early Wednesday morning, successfully completing a complex maneuver that will help scientists better understand one of the solar system's most intriguing moons.

Beginning around midnight, a team of scientists and engineers guided the spacecraft into an orbit that allowed them to bounce a radio signal off the surface of Titan toward Earth, where it was received by a land-based telescope array 1 billion miles away.

"We are essentially using Titan as a mirror," said Essam Marouf of San Jose State University, who's a member of the Cassini radio science team. "And the nature of the echo can tell us about the nature of Titan's surface, whether it is liquid or solid, and the physical properties of the material."

Saturn's moon Titan is the second-largest moon in the solar system after Jupiter's moon Ganymede, and in some ways it's one of the most Earth-like bodies we have encountered.

Like Earth, it has a thick atmosphere, and it is the only other world we know of that has a system of liquid lakes and seas on its surface.

However, unlike Earth, its surface is far too cold to sustain liquid water.

Scientists have hypothesized that Titan's famous lakes and seas are made of liquid methane or ethane, but Marouf explains that those inferences are mostly based on the fact that methane and ethane would take on a liquid state in the conditions on Titan, rather than direct observation.

"There is no really direct measurement that tells us what they are exactly," he said.

"If the data from this morning is good enough, it will tell us what these liquids really are."

From 11:30 Tuesday evening to 11 Wednesday morning, Marouf gathered with other members of Cassini's radio science team in a control room at the Jet Propulsion Laboratory in La Canada Flintridge near downtown Los Angeles, watching as the new data were received by a radio telescope array in Australia.

He said they could not analyze the data in real time, but they were able to tell that the signal was clear enough to give them something to work with.

Cassini performed a similar experiment on Saturn's surface on May 17 that was also a success. That time, the researchers were able to collect information from two of the largest bodies of liquid on Titan: Ligea Mare and Kraken Mare.

This time, Cassini bounced its radio signal off an area between the two seas where radar images had found smaller liquid regions similar to rivers, lakes and channels on Earth.

"This kind of experiment takes a meticulous kind of preparation to first know where to look, and then design the maneuvers," Marouf said. "There are many pieces that have to work flawlessly to end up with the data."

He said the team hopes to look over the data this week and share its early results at a Cassini science team meeting next week in the Netherlands.

NASA Cassini Titan Research: Ice On A Hydrocarbon Lake

This artist's concept envisions what hydrocarbon ice forming on a liquid hydrocarbon sea of Saturn's moon Titan might look like. 

A new model from scientists on NASA's Cassini mission suggests that clumps of methane-and-ethane-rich ice could float under some conditions. They are shown here as the lighter-colored clusters.

A new paper by scientists on NASA's Cassini mission finds that blocks of hydrocarbon ice might decorate the surface of existing lakes and seas of liquid hydrocarbon on Saturn's moon Titan.

The presence of ice floes might explain some of the mixed readings Cassini has seen in the reflectivity of the surfaces of lakes on Titan.

"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 while our planet's cycle of precipitation and evaporation involves water, Titan's cycle involves hydrocarbons like ethane and methane.

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 bejewels the southern hemisphere.

Titan: The rover boat that could explore Saturn's moon

Mars may grab all the headlines, but the Red Planet isn't the only Earth-like body in our solar system.

Saturn's moon Titan has long sparked the interest of scientists because its surface is covered in lakes, and rivers — which are filled with liquid methane.

Now, a group of engineers have submitted their plans for a new kind of rover — a floating space boat to rival NASA's Curiosity.

The Titan Lake In-situ Sampling Propelled Explorer, or TALISE, would succeed the ESA's Huygens probe, which touched down on Titan in 2005 after a seven-year journey.

TALISE would weigh about 100 kilograms (220.5 lbs), and would be equipped with an assortment of scientific instruments including a magnetometer, a panoramic camera, an acoustic sounder and a Light Detection And Ranging (LiDAR) system.

It would move across the surface of the liquid hydrocarbons using either smooth wheels, paddle wheels, or screw drives – all three systems are currently being considered.

Earlier ideas that were ultimately rejected included tank tracks, above- and below-surface propellers, and a hovercraft design.

After landing, TALISE will explore and collect data from the liquid methane makeup of the lakes found on the moon's surface.

SENER, a private aerospace company, is working in collaboration with Spain's Centro de Astrobiologia to develop a propulsion system that would allow TALISE to navigate on both land and sea, using a combination of wheels and paddles.

ESA Saturn Titan: Far-off cousin of part-time African lake found on Titan

A region on Saturn’s moon Titan has been found to be similar to the Etosha Pan in Namibia, Africa. Both are ephemeral lakes – large, shallow depressions that sometimes fill with liquid.

Ontario Lacus is the largest lake in the southern hemisphere of Saturn’s moon, Titan. It is a little smaller than its namesake, Lake Ontario in North America, but otherwise differs from it in some major ways.

It is filled with liquid hydrocarbons, not water, and it is only a few metres deep at most, located in an extremely shallow depression in a flat sedimentary basin, surrounded by small mountain ranges.

In addition, a new study shows that these landforms and the climatic conditions in the region are similar to those of semi-arid regions on Earth, such as the salt pans of southern Africa.

The observations were made by the Cassini orbiter, part of the NASA, ESA and Italian Space Agency Cassini–Huygens mission to Saturn’s system.

While Ontario Lacus was previously thought to be permanently filled with liquid methane, ethane and propane, these latest observations, published in the journal Icarus, suggest otherwise.

By combining data from Cassini’s imaging, spectroscopic and radar instruments – each of which observed Ontario Lacus twice – scientists led by Thomas Cornet of the Université de Nantes, France, found evidence for channels etched into the lake bed within the southern boundary of the depression. These channels remained visible between December 2007 and January 2010, each time the spatial resolution was able to resolve them.

“We conclude that the solid floor of Ontario Lacus is most probably exposed in those areas,” says Cornet.

In addition, Cassini shows sediments around Ontario Lacus that also indicate the liquid level has been higher in the past.

This is similar to ephemeral lakes on Earth. The researchers suggest its nearest cousin is the Etosha Pan in Namibia. This salt lake bed fills with a shallow layer water, provided by the rise of the underground aquifer during the rainy season, before evaporating to leave sediments like tide marks showing the previous extent of the water.

Cornet and colleagues thus believe that Ontario Lacus is also the result of subsurface hydrocarbon fluids occasionally welling up and flooding the depression, before then partially drying out again.

Beyond Earth, Titan is the only other world known to bear stable liquids on its surface. Where Earth has a water cycle, Titan has a full hydrocarbon cycle, based on hydrogen, carbon and nitrogen, taking place between the atmosphere, the surface and the subsurface. Titan’s lakes are an integral part of this process.

“These results emphasise the importance of comparative planetology in modern planetary sciences: finding familiar geological features on alien worlds like Titan allows us to test the theories explaining their formation,” says Nicolas Altobelli, ESA’s Cassini–Huygens project scientist.

Cassini Solstice Mission: Titan's Kraken Mare

The Cassini spacecraft looks toward Saturn's largest moon, Titan, and spies the huge Kraken Mare in the moon's north.

Kraken Mare, a large sea of liquid hydrocarbons, is visible as a dark area near the top of the image.

See Titan's Northern Polar Clouds and Titan's Northern Lake to learn more.

This view looks toward the Saturn-facing side of Titan (3,200 miles across, or 5,150 kilometers,).

North on Titan is up and rotated 29 degrees to the left.

The image was taken with the Cassini spacecraft narrow-angle camera on Sept. 14, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 26 degrees. Image scale is 7 miles (12 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov or http://www.nasa.gov/cassini . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL-Caltech/Space Science Institute

NASA Cassini spacecraft: Saturn's Moon Titan's North Polar Region

NASA's Cassini spacecraft will be eyeing the north polar region of Saturn's moon Titan this weekend, scanning the moon's land o' lakes.

At closest approach on early morning Saturday, June 5 UTC, which is Friday afternoon, June 4 Pacific time, Cassini will glide to within about 2,000 kilometers (1,300 miles) of the Titan surface.

Cassini will make infrared scans of the north polar region, which was in darkness for the first several years of Cassini's tour around the Saturn system. The lighting has improved as northern spring has started to dawn over the area.

The visual and infrared spectrometer will be prime during closest approach, but the imaging science subsystem cameras will also be taking pictures. Among the scientific bounties, Cassini team members are hoping to get another good look at Kraken Mare, the largest lake on Titan, which covers a greater area than the Caspian Sea on Earth.

Although this latest flyby is dubbed "T69," planning changes early in the orbital tour made this the 70th targeted flyby of Titan.

Life found on Saturn moon - Titan

Hydrocarbon lakes on Titan may harbour exotic forms of life (Illustration: NASA/JPL)

Hints of life found on Saturn moon

Two potential signatures of life on Saturn's moon Titan have been found by the Cassini spacecraft. But scientists are quick to point out that non-biological chemical reactions could also be behind the observations.

Titan is much too cold to support liquid water on its surface, but some scientists have suggested that exotic life-forms could live in the lakes of liquid methane or ethane that dot the surface.

In 2005, Chris McKay of NASA's Ames Research Center in Moffett Field and Heather R Smith of the International Space University in Strasbourg, France, calculated that such microbes could eke out an existance by breathing in hydrogen gas and eating the organic molecule acetylene, creating methane in the process.

This would result in a lack of acetylene on Titan and a depletion of hydrogen close to the moon's surface, where the microbes would live, they said.

Now, measurements from the Cassini spacecraft have borne out these predictions, hinting that life may be present.

Hungry for hydrogen

Infrared spectra of Titan's surface taken with the Visual and Infrared Mapping Spectrometer (VIMS) showed no sign of acetylene, even though ultraviolet sunlight should constantly trigger its production in the moon's thick atmosphere.

Cassini measurements also suggest hydrogen is disappearing near Titan's surface, according to a study to appear in Icarus.

Observations with the spacecraft's Ion and Neutral Mass Spectrometer and its Composite Infrared Spectrometer revealed that hydrogen produced by UV-triggered chemical reactions in the atmosphere is flowing both upwards and off into space as well as down towards the surface.

Titan: Saturn's moon hydrocarbon lakes

Saturn's frigid moon Titan may be friendlier to life than previously thought. New calculations suggest Titan's hydrocarbon lakes are loaded with acetylene, a chemical some scientists say could serve as food for cold-resistant organisms.

At about -180 °Celsius, Titan's surface is far too cold for liquid water. But two pairs of scientists proposed in 2005 that alien organisms might live instead in bodies of liquid hydrocarbons on the frigid moon. They suggested such organisms could eat acetylene that falls to the surface after forming in the atmosphere, combining it with hydrogen to gain energy.

Since then, Titan has spotted dozens of lakes on Titan's surface, thought to be made of a mixture of liquid ethane and methane. But since no probe has directly sampled them, no one knows how much acetylene they might contain.

An estimate made in 1989 suggested bodies of liquid hydrocarbons on Titan would contain a few parts in 10,000 of acetylene.

But an updated estimate based on data from the Cassini-Huygens mission to Saturn now suggests the lakes contain much more food for any hungry alien life-forms that might be present. The new calculations were made by a team of scientists led by Daniel Cordier of the Ecole Nationale Supérieure de Chimie de Renne, France.

Right temperature
Data from the Cassini spacecraft and the Huygens probe, which parachuted to Titan's surface in 2005, helped Cordier's team re-calculate the lakes' likely composition. This depends on factors like a lake's temperature, which affects how easily chemicals will dissolve in it, and the rate various chemicals are produced in the atmosphere and rain onto the surface.

The team found that acetylene would be hundreds of times as abundant as the previous estimate, making up one part in 100 of the lake's content.

"Having about a per cent of acetylene is potentially interesting from the life point of view," says team member Jonathan Lunine of the University of Arizona in Tucson. The idea of acetylene-eating organisms on Titan is "highly speculative" but intriguing, he says