Titan’s Chemistry : Exobiological Aspects and Expected Contribution from Cassini-Huygens

Abstract

Because of the presence of a dense atmosphere, of an environment very rich in organics, and of many couplings involved in the various parts of its “geofluid”, Titan, the largest satellite of Saturn, is a reference for studying prebiotic chemistry on a planetary scale. By coupling the data obtained from simulation experiments carried out in the laboratory, theoretical modeling and observations, it is already possible to draw a quite precise figure of such organic chemistry, with all its complexity. In particular, new data have been obtained from experiments simulating the organic chemistry of Titan’s atmosphere (gas and aerosol phases), in an open reactor, within the correct range of temperature, pressure, carefully avoiding any chemical contamination. They show a very good agreement with the observational data, demonstrating for the first time the formation of all the organic species already detected in Titan’s atmosphere. In particular, C4N2, never detected before in this kind of laboratory experiment, although it has been detected in Titan’s atmosphere, is now clearly identified, together with many other species not yet detected in Titan. This strongly suggests the presence of more complex organics in Titan’s atmosphere and surface, including high molecular weight polyynes and cyanopolyynes. The NASA-ESA Cassini-Huygens mission was successfully launched in October 1997. The Cassini spacecraft will reach the Saturn system in 2004 and will become an orbiter around Saturn and fly-by Titan, while, simultaneously it will send the Huygens probe into Titan’s atmosphere. Both will systematically study organic chemistry in Titan’s “geofluid”. In situ measurements, in particular from Huygens GC-MS and ACP instruments, will provide detailed analysis of the organics present in the air, aerosols, and surface. This very ambitious mission should provide much information of crucial importance for our knowledge of the complexity of Titan’s chemistry, and, more generally for the field of exobiology.