The European Space Agency's and NASA's Saturn mission has beamed back images of shifting dunes on the surface of the giant moon Titan (see right). Cassini's radar imager found the Earth-like desert landscapes dominating huge swathes of the moon's surface near the equator.

The dunes are up to 150m high and can span hundreds of kilometres, according to researchers reporting in Science. Their length, width and spacing means they are the spitting image of deserts in Namibia and Arabia. It's not known what makes up the dunes' “sand”. The prime suspects are carbon-based material annealing in the atmosphere, and water ice grains created by methane rains on Titan's -180°C surface.

The new data puts the mockers on the interpretation that dark patches seen near the equator are seas.

The dunes are oriented east to west, indicating the prevailing winds in Titan's 98 per cent nitrogen atmosphere. The fine grained dunes mean scientists can infer that winds are strong enough to erode some surface material.

It had been thought that the sunlight reaching Titan is too weak to drive strong wind systems, but recent data suggests the pull of Saturn's gravity may be enough. Titan's “deserts” also indicate a fluctuating north-south “tidal” component to the dune's shifting caused by the mother planet's pull.

Last year, Cassini sent the Huygens lander to the surface of Titan, the largest of Saturn's bumper litter of 47 satellites. It sent back spectacular video of its descent which has just been released and can be viewed here.®

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