Post by Dr. A Lucas, CNRS Research Scientist, Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005, Paris, France

Titan, Saturn’s largest satellite, has proved to be a world that is both strange and yet so familiar to us. Mountains, lakes, drainage systems and dune fields (Images 1-2) cover its surface. Methane on Titan occupies a similar position to water on Earth. It participates in climatic cycles. Moreover, its photodissociation in the upper atmosphere is responsible for the soot rains that fall on the surface of this icy world. The fate of these grains composed of organic materials is just as essential. Indeed, winds sometimes mobilize them. Over long, very long periods of time, this granular transport is responsible for the formation of vast dune fields located at the equator. But after 13 years of exploration by the Cassini probe, these dunes have not revealed all their secrets. In particular, their morphodynamics are widely debated. Are these bedforms remains from an old time, are they still active today? What is their growth rate? And what is their resulting sediment flux?

Image 1: Despeckled T8 swath SAR image over the Belet sand dunes located at the Equator of Titan. The dark longitudinal features are the micro-wave absorbent dunes composed of sand made of organics molecules. The bright areas are rough topographic reliefs revealing the icy bedrock beneath the organic sediment cover. Glints (bright spots) are detectable of the crest of some dunes due to specular reflection on their avalanche side.

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