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.

ESA Huygens lander, full size replica, London Science Museum

ESA's Saturn Huygens lander, full size replica, London Science Museum.

NASA Cassini: Saturn's Moon Enceladus Image

This view of Saturn's moon Enceladus were made from data obtained by NASA's Cassini spacecraft during this week's flyby. Image credit: NASA/JPL/SSI/LPI.
 

Raw, unprocessed images from the successful Oct. 19 flyby of Saturn's moon Enceladus by NASA's Cassini spacecraft provide new views of the moon and the icy jets that burst from its southern polar region.

This flyby gave Cassini its first opportunity to observe Enceladus' plumes with two stars shining behind them, a dual stellar occultation.

Cassini flew within about 765 miles (1,230 kilometers) of Enceladus' surface on Oct. 19.

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.

NASA - Saturn's Moon Enceladus Spreads its Influence

Chalk up one more feat for Saturn's intriguing moon Enceladus.

The small, dynamic moon spews out dramatic plumes of water vapor and ice -- first seen by NASA's Cassini spacecraft in 2005.

It possesses simple organic particles and may house liquid water beneath its surface.

Its geyser-like jets create a gigantic halo of ice, dust and gas around Enceladus that helps feed Saturn's E ring.

Now, thanks again to those icy jets, Enceladus is the only moon in our solar system known to influence substantially the chemical composition of its parent planet.

In June, the European Space Agency announced that its Herschel Space Observatory, which has important NASA contributions, had found a huge donut-shaped cloud, or torus, of water vapor created by Enceladus encircling Saturn.

The torus is more than 373,000 miles (600,000 kilometers) across and about 37,000 miles (60,000 kilometers) thick. It appears to be the source of water in Saturn's upper atmosphere.

Though it is enormous, the cloud had not been seen before because water vapor is transparent at most visible wavelengths of light. But Herschel could see the cloud with its infrared detectors.

"Herschel is providing dramatic new information about everything from planets in our own solar system to galaxies billions of light-years away," said Paul Goldsmith, the NASA Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The discovery of the torus around Saturn did not come as a complete surprise. NASA's Voyager and Hubble missions had given scientists hints of the existence of water-bearing clouds around Saturn.

Then in 1997, the European Space Agency's Infrared Space Observatory confirmed the presence of water in Saturn's upper atmosphere. NASA's Submillimeter Wave Astronomy Satellite also observed water emission from Saturn at far-infrared wavelengths in 1999.

While a small amount of gaseous water is locked in the warm, lower layers of Saturn's atmosphere, it can't rise to the colder, higher levels.

To get to the upper atmosphere, water molecules must be entering Saturn's atmosphere from somewhere in space. But from where and how? Those were mysteries until now.

Build the model and the data will come.

NASA - Saturn's Moon Enceladus Spreads its Influence

ESA: Enceladus rains water onto Saturn - images

At least four distinct plumes of water ice spew out from the south polar region of Saturn's moon Enceladus.

Light reflected off Saturn is illuminating the moon while the sun, almost directly behind Enceladus, is backlighting the plumes.

This view looks toward the Saturn-facing side of Enceladus (504 kilometers across). North is up.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 25, 2009.

The view was obtained at a distance of approximately 617,000 kilometers from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 174 degrees. Image scale is 4 kilometers per pixel.

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

Credits: NASA/JPL/Space Science Institute

Cassini radar sees sand dunes on Saturn's giant moon Titan

Image credit: NASA/JPL (upper photo); NASA/JSC (lower photo)

Cassini radar sees sand dunes on Saturn's giant moon Titan (upper photo) that are sculpted like Namibian sand dunes on Earth (lower photo).

The bright features in the upper radar photo are not clouds but topographic features among the dunes.

The answer to the mystery of dune patterns on Saturn's moon Titan did turn out to be blowing in the wind. It just wasn't from the direction many scientists expected.

Basic principles describing the rotation of planetary atmospheres and data from the European Space Agency's Huygens probe led to circulation models that showed surface winds streaming generally east-to-west around Titan's equatorial belt.

But when NASA's Cassini spacecraft obtained the first images of dunes on Titan in 2005, the dunes' orientation suggested the sands - and therefore the winds - were moving from the opposite direction, or west to east.

A new paper by Tetsuya Tokano in press with the journal Aeolian Research seeks to explain the paradox. It explains that seasonal changes appear to reverse wind patterns on Titan for a short period. These gusts, which occur intermittently for perhaps two years, sweep west to east and are so strong they do a better job of transporting sand than the usual east-to-west surface winds.

Those east-to-west winds do not appear to gather enough strength to move significant amounts of sand.

A related perspective article about Tokano's work by Cassini radar scientist Ralph Lorenz, the lead author on a 2009 paper mapping the dunes, appears in this week's issue of the journal Science.

"It was hard to believe that there would be permanent west-to-east winds, as suggested by the dune appearance," said Tokano, of the University of Cologne, Germany. "The dramatic, monsoon-type wind reversal around equinox turns out to be the key."

The dunes track across the vast sand seas of Titan only in latitudes within 30 degrees of the equator. They are about a kilometer (half a mile) wide and tens to hundreds of kilometers (miles) long. They can rise more than 100 meters (300 feet) high.

The sands that make up the dunes appear to be made of organic, hydrocarbon particles. The dunes' ridges generally run west-to-east, as wind here generally sheds sand along lines parallel to the equator.

Scientists predicted winds in the low latitudes around Titan's equator would blow east-to-west because at higher latitudes the average wind blows west-to-east. The wind forces should balance out, based on basic principles of rotating atmospheres.