Saturn's Moon Titan: Methane Lakes Drying Up

This artist concept shows a mirror-smooth lake on the surface of the smoggy moon Titan.

These lakes are liquid hydrocarbon (methane) and not water.

CREDIT: NASA/JPL

Today, methane sloshes around in pools on the surface of Saturn's Titan, but the hydrocarbon may eventually vanish from Saturn's giant moon, according to a new study.

Images and data from NASA's Cassini spacecraft show that the compound doesn't seem to be getting replenished fast enough on Titan's surface to keep the methane cycle sustainable, scientists say.

Besides Earth, Titan is the only known place in our solar system to have stable liquids on its surface. The huge moon's clouds, lakes and rain are made up of hydrocarbons, or molecules composed of hydrogen and carbon, such as methane and ethane.

Cassini images have revealed that Titan's hydrocarbon lakes stay remarkably consistent in size and shape over time.

This means that either the lakes evaporate at a crawling pace, or there are enough downpours to offset the evaporation.

Rain Clouds
Since scientists have observed only occasional bursts of rain on Titan, they believe that the lakes must have quite stable, slowly evaporating contents, and may be dominated by ethane, which doesn't vanish as quickly as methane.

Christophe Sotin

When methane floats high into Titan's soupy atmosphere, the compound is broken apart by sunlight. Many of its hydrogen atoms keep rising and disappear into space, while the remaining elements go on to make carbon-rich products like ethane.

Scientists say this process should eventually diminish the overall amount of methane in Titan's environment, as compounds pieced together out of methane's leftovers continue to get dumped on the moon's surface.

"We are seeing an active Titan whose active chemistry may come to an end in some tens of million years," said Christophe Sotin, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who has been analyzing Cassini measurements of Titan's lakes and seas.

That might sound like a long time away, but it could mean that Titan's "methane era" is somewhat short-lived, at least on a geological timescale.