MightyMartian writes "NASA scientists say Cassini has discovered that far fewer craters are visible on Titan than on the other moons of Saturn. The craters they have discovered are far shallower than other moons' craters and appear to be filling with hydrocarbon sand. On top of being another reason Titan's active geology is very cool, it adds to the mystery of where all the methane on Titan is coming from. 'The rain that falls from Titan's skies is not water, but contains liquid methane and ethane, compounds that are gases at Earth's temperatures. ... The source of Titan's methane remains a mystery because methane in the atmosphere is broken down over relatively short time scales by sunlight. Fragments of methane molecules then recombine into more complex hydrocarbons in the upper atmosphere, forming a thick, orange smog that hides the surface from view. Some of the larger particles eventually rain out onto the surface, where they appear to get bound together to form the sand.'"