How wind forms the dunes of Saturn's moon, Titan
Around the equator of Saturn’s moon Titan, massive tar-coloured dunes stretch for hundreds of kilometres. Some are 100 metres high and a kilometre or more wide from the base.
Titan poses many mysteries. It is the only body in the solar system, aside from Earth, that has liquid reservoirs on its surface – although its lakes and rivers are filled with methane and ethane. The atmosphere of Titan is 95% nitrogen and 5% methane, and it is about 1.5 times as dense as the atmosphere on Earth.
Venus and Mars also have dunes, but Titan is the only moon that has them. They are made of a finer, lighter and more powdery substance than the sand on Earth’s dunes – scientists believe they consist of hydrocarbons and may include water ice particles. (Titan is cold. Its temperature is negative 147 Celsius).
To understand how the dunes formed, scientists recreated conditions on Titan in a wind tunnel in Arizona State University’s Planetary Aeolian Laboratory. The wind tunnel was originally built in the 1980s to simulate conditions on Venus.
The researchers found it would take a slow wind of 5.1 kmh per hour to move Titan’s “sand”. The results have been published in Nature.
“It still seems really slow, but it turns out that winds on Titan are really slow because there is no real temperature difference or pressure difference to drive fast winds,” said co-author of the paper Joshua Emery from the University of Tennessee.
For a separate paper published in Nature Geoscience, researchers studied the Cassini space mission's images of Titan's dunes. They concluded the dunes would have taken at least 3,000 Saturn years (or 88,000 Earth years) to form.