The Cassini-Huygens probe, currently in orbit around Saturn, regularly carries out overflights of the major satellites of this planet. A principal objective of this NASA-ESA joint mission is in particular the study of Titan, the second larger satellite of the solar system with its 5150 km in diameter. Because of its permanent atmosphere, primarily made up of nitrogen and containing methane as well as organic compounds, the surface of Titan is invisible for sensors functioning in the visible and infra-red, except for some rare windows. The surface of the satellite was partly revealed by the Huygens probe of ESA, which landed in an area close to the equator on January 14, 2005 : the cameras of Huygens have shown structures resembling drainage networks and dry lakes. The Radar instrument of the Cassini orbitor is a system at hyper frequencies (Ku band) which allows to study the surface of Titan through its opaque atmosphere. This instrument operates in radiometer mode, scatterometer, altimeter and SAR imager. It is the latter mode which allows to observe the surface of Titan to a resolution better than the kilometer. It already allowed the discovery of several cryo-volcanic structures, of craters of impact and vast fields of dunes. The T16 flight carried out over the North Pole of Titan on July 22, 2006 revealed more than 75 radar-dark structures, of irregular shapes, reaching up to several tens of kilometers, in an region where liquid methane and ethane are expected to be abundant. The structures discovered have clear lake morphologies and are associated to topographic channels and depressions. All indicates that these are the first extraterrestrial lakes discovered in our solar system, confirming that an active hydrological cycle exists on the surface and in the atmosphere of Titan.
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Contact Pierre Encrenaz (Prof. at Univ. P&M Curie and Observatoire de Paris, LERMA et CNRS )
Dernière modification le 18 octobre 2013