For all of its differences, the surface of Titan – Saturn’s largest moon – has a couple of key similarities with Earth that make it an important subject for researchers. It has a thick atmosphere and is the only other body in the solar system with liquid on the surface, though temperatures far below freezing mean that it has lakes of liquid natural gas instead of water.
One particular feature that has had scientists confused are the sand dunes across Titan’s surface that run hundreds of miles long and appear to have been formed by winds blowing from west to east, while Titan’s prevailing winds are known to blow in the opposite direction.
“The dunes are not made of silicates – sand – as on Earth or Mars,” says UT Knoxville planetary scientist Devon Burr, who seems to have cracked the problem in a paper being published with co-author John Marshall in Nature, the SETI Institute reports. “They’re hydrocarbons, and may possibly include particles of water ice that are coated with these organic materials.”
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Dunes created by rare, intense winds
Even though the dunes may appear symmetric for much of their extent, when they wrap around mountains and other obstacles that would block the wind, that symmetry breaks down and scientists can see which direction the wind that formed them came from.
What Burr realized, using a specialized wind tunnel to run simulations, was that the typical winds blowing across Titan’s surface aren’t strong enough to move this mix of hydrocarbons around very much. But the wind occasionally switches direction in a rare but intense event caused by the changing position of the Sun in Titan’s sky that the researchers compare to ‘perfect storms’ at sea. It turns out that the shape of the dunes is determined by these occasional events and then remains relatively static the vast majority of the time.
Terrestrial applications of Burr’s research
Burr says that these results have practical applications here on earth as well.
“We see today sediment being wafted over the Sahara desert, across the Atlantic to South America. This wind-blow material accounts for much of the fertility of the Amazon Basin. So understanding this process is essential,” says Burr.
Even though we don’t have lakes have liquid methane, advances in modeling wind formation of surface structures in general helps scientists working on other problems like the ones that Burr mentions.