Saturn's largest moon apparently is lashed regularly by rain made of liquid methane, forming pools, cutting river beds and eroding rocks in much the same way that forces have shaped the Earth
Black-and-white photos from the Huygens probe show a rugged terrain of ridges, peaks, dark vein-like channels and apparently dry lakebeds on the moon 744 million miles away.
On Earth, methane is a flammable gas. On Titan, it is a liquid because of the intense pressure and cold -- 274 degrees below zero.
A sensor about the size of a police officer's nightstick on the front of Huygens probed beneath the moon's crust and found a material with the consistency of loose sand.
Channels on the surface are evidence of methane rain. There are also what appear to be river systems and deltas, frozen protrusions riddled by channels, apparent dried-out pools where liquid has perhaps drained away, and stones -- probably ice pebbles -- that seem to have been rounded by erosion.
The river beds are darkened by what seem to be particles of smog that fall out of Titan's atmosphere, coating the terrain. The dirt apparently gets washed off the ridges by the methane rain to collect in the river channels.
Scientists believe the dark smog particles are formed by Titan's methane breaking up in the atmosphere.
Lebreton, the mission manager, said a next possible step in Titan exploration would be to send mobile probes, perhaps balloons to float around before landing.
