Titan's siblings must be jealous. While most of Saturn's moons display their ancient faces pockmarked by thousands and thousands of craters, Titan - Saturn's largest moon - may look much younger than it really is because its craters are getting erased.
"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 radar team associate based at NASA's Goddard Space Flight Center, Greenbelt, Md. "It's possible that there are many more craters on Titan, but they are not visible from space because they are so eroded. 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.
"This research is the first quantitative estimate of how much the weather on Titan has modified its surface," adds Neish. Titan is the only moon in the solar system with a thick atmosphere, and the only world besides Earth known to have lakes and seas on its surface. However, Titan has a frigid surface temperature of around minus 290 degrees Fahrenheit (94 kelvins). 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. Neish and her team compared craters on Titan to craters on Jupiter's moon Ganymede. Ganymede is a giant moon with a water ice crust, similar to Titan, so craters on the two moons should have similar shapes. However, Ganymede has almost no atmosphere and thus no wind or rain to erode its surface. "We found that craters on Titan were on average hundreds of yards [meters] shallower than similarly sized craters on Ganymede, suggesting that some process on Titan is filling its craters," says Neish, who is lead author of a paper about this research published online in the journal Icarus on Dec. 3, 2012.