New findings from NASA's Cassini probe have revealed that Saturn's moon Titan may look younger than it really is. Dunes of hydrocarbon sand have been slowly filling up the craters that pockmark the moon.
"Most of the Saturnian satellites - Titan's siblings - have thousands and thousands of craters on their surface," said Catherine Neish, a Cassini radar team associate based at NASA's Goddard Space Flight Center. "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. 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."
The new research is the first quantitative estimate of how much the weather on Titan has eroded its surface. The moon is the only one known in our solar system to have a thick atmosphere. It is also known to have seas of organic compounds, such as ethane and methane, on its surface.
Methane is broken down in Titan's atmosphere by sunlight, then recombined into more complex hydrocarbons. These molecules form an orange smog that envelops the planet. Some of the larger particles from the atmosphere, say scientists, rain down and become bound together into an exotic form of sand.
"Since the sand appears to be produced from the atmospheric methane, Titan must have had methane in its atmosphere for at least several hundred million years in order to fill craters to the levels we are seeing," said Neish.
Titan's methane levels are somewhat of a mystery, however. Researchers estimate that current levels of methane on Titan would be broken down within tens of millions of years. This suggests that the moon either had much more methane in the past, or is replenishing its methane in some way.
(Image courtesy NASA/JPL-Caltech/ASI/GSFC)