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Tuesday, July 25, 2006 

Titan may be a land of lakes after all

At last, we know that Titan has lakes. Probably. NASA's Cassini spacecraft buzzed the giant moon again this weekend, and raked its radar beam across Titan's north pole. The image it returned shows black patches near the pole, some of them apparently fed by drainage channels.

The darkness of these areas implies that none of the radar beam bounced back to Cassini. The most likely explanation is that it hit a very smooth surface – probably liquid methane or ethane, which are stable at the -180°C temperatures of Titan's surface. If this is truly the case, then Titan is only the second body known to have surface liquids, after the Earth.

Earlier images from Titan also showed dark patches that were considered possible lakes, but they were less dark. "In this case it is much clearer. The contrast is so great that there are few doubts that the surface is a liquid one," says Enrico Flamini of the Italian Space Agency in Rome, a member of the radar instrument team.

The lakes are presumably filled by rainfall, perhaps by seasonal storms, and then evaporate slowly to replenish the atmosphere and complete Titan's methane cycle. The largest of the apparent lakes osbserved are around 100 kilometres across – a little too small to be called seas – as well as a network of smaller, interconnected lakes resembling parts of Finland and Canada. Some have rims that might be deposits left behind as the methane evaporates. >> more