Paris (AFP)

Dunes, plains, lakes, mountains ... Hidden behind a misty atmosphere, Titan has varied landscapes according to a global cartography, published Monday in Nature Astronomy, the largest moon of Saturn.

"Titan is the only known extraterrestrial object to have liquid expanses on its surface," notes Alice Le Gall of Paris-Saclay University, co-author of the study, referring to her hydrocarbon lakes.

On Titan, methane and ethane can exist in all three states: solid, liquid, and gas on the surface. So there is a cycle of methane (and ethane) comparable to that of water on Earth. That is to say clouds that precipitate and feed the rivers and lakes (even an underground liquid reservoir), etc., "says the researcher AFP.

By combining data from different instruments of the Cassini mission (radar images and infrared spectrometer observations), a team of researchers led by Rosaly Lopes of the California Institute of Technology (Caltech) in the United States was able to identify six major geological terrains on Titan.

"The distribution of these lands is fairly compartmentalized: the dunes are in the equatorial belt of Titan, where the weather is probably the most arid, the plains are at mid-latitudes, lakes and labyrinthine terrains at the poles (where it rains the most), "says the researcher.

To complete the portrait of Titan, curious star where it is -180 ° C, larger than Mercury and our Moon, we must add mountains "everywhere", and some craters. On the other hand, even if the satellite is composed of at least 50% of ice, the latter is little present on its surface.

"Indeed, the UV rays of the Sun permanently break the nitrogen and methane molecules in Titan's atmosphere, which recombine to form, among other things, organic aerosols (solid particles) that are deposited on the surface. , covering it with a kind of organic soot and masking the underlying ice (except perhaps in the mountains) ", explains Alice Le Gall.

According to the study published in the journal Nature Astronomy, Titan's dunes are enormous, measuring hundreds of kilometers long and a few kilometers wide. And the plains, "relatively uniform terrain with no particular characteristics", are by far the most abundant (65% of the surface area).

"But maybe some of these plains are covered with + small + dunes or + small + rivers that can not be seen with the Cassini instruments," says Alice Le Gall.

© 2019 AFP