Titan: an astrobiological laboratory in the solar system

摘要

After only three years of close observation from the Cassini-Huygens mission, Titan appears more and more as one of the key planetary bodies in the solar system for astrobiological studies Titans does not look any more like a frozen primitive Earth, but like an evolving planet, geologically active, with cryovolcanism, eolian erosion, clouds and precipitations, and a methane cycle very similar to the water cycle on Earth The new data also show a very complex organic chemistry in the highest atmospheric zones of the satellite, with the formation in the ionosphere of high molecular weight organics feeding the lower zones, down to the surface, In spite of the low surface temperature, these organics are probably evolving once in contact with water ice and form organic molecules of biological interest. This may explain the reflectance spectrum of Titan' surface observed by the DIRS instrument on Huygens. Thus, contrary to what was expected, the organic chemistry on Titan seems mainly concentrated in the ionosphere, in the aerosols and on the surface. These astrobiological aspects of Titan are presented and discussed on the basis of the already available Cassini-Huygens data, as well as the needed post Cassini exploration.