for National Geographic News
Saturn's giant moon has lakes and a "water" cycle remarkably similar to Earth's, new evidence suggests.
But Titan's lakes aren't made of water. Instead, they probably consist of liquid methane, which plays the role of water in Titan's superchilled climate, the researchers say.
The lakes were discovered by radar mapping when the Cassini spacecraft, now orbiting Saturn, did a close flyby of northern Titan last July.
The flyby revealed dozens of large, dark patches resembling lakes, up to 40 miles (70 kilometers) in diameter. (See more Saturn photos from Cassini.)
When the lakes were first discovered, the scientists noticed riverlike drainage channels that probably conducted moisture from the surrounding highlands.
This indicates that the lakes were fed by methane rains falling at higher elevations, said Ellen Stofan, lead author of a study in yesterday's issue of the journal Nature.
But some lakes had no such inlet streams. That means that there must be methane aquifers—"methanofers," Stofan called them—not far below the surface.
"Just like on Earth, if you dig deep enough, the depression fills up with water," said Stofan, who shares her time between the Proxemy Research corporation in Virginia and University College London in England. "There's a subsurface methane table."
Some of Titan's lakes also appear to lie in calderas formed by "cryovolcanism," but this doesn't mean that the methane in these lakes came from the volcanoes.
"Just like at Crater Lake in Oregon, once you have a depression, it will fill up with liquid," Stofan says.
Just Like Earth
Like other Titan researchers, Stofan is amazed by how many similarities Titan has to Earth.
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