Observations by NASA's Cassini spacecraft suggest dunes of exotic, hydrocarbon sand are slowly but steadily filling in Titan's craters, they said.
"Most of the Saturnian satellites -- Titan's siblings -- have thousands and thousands of craters on their surface. So far on Titan, of the 50 percent of the surface that we've seen in high resolution, we've only found about 60 craters," said Catherine Neish, a Cassini mission scientist at NASA's Goddard Space Flight Center, Greenbelt, Md.
"We typically estimate the age of a planet's surface by counting the number of craters on it (more craters means an older surface). But if processes like stream erosion or drifting sand dunes are filling them in, it's possible that the surface is much older that it appears," she said in a NASA release Thursday.
Titan's atmosphere is mostly nitrogen with a trace of methane and other, more complex molecules made of hydrogen and carbon that eventually rain out onto the surface, where they appear to get bound together to form the sand, she said.
The researchers compared craters on Titan to craters on Jupiter's moon Ganymede, which, although similar in many ways to Titan, has no atmosphere and thus no wind or rain to erode its craters.
"We found that craters on Titan were on average hundreds of yards shallower than similarly sized craters on Ganymede, suggesting that some process on Titan is filling its craters," Neish said.