The Cassini-Huygens ACP experiment and exobiological implications

Abstract : Since the discovery of its dense nitrogen atmosphere Titan, the largest satellite of Saturn has always been the subject of a strong interest by the scientific community of the exobiologists. The main reason is that Titan's atmosphere is believed to be over geologic time a permanent source of N-containing organic molecules (mostly nitriles) and of various hydrocarbons. Some of these species polymerize to form very complex organic chains which condense into aerosols. The result of this microphysical and photochemical activity is that substantial organic sediments may have accumulated on Titan's surface. The objectives of the Aerosol Collector Pyrolyser (ACP) instrument of the Huygens Probe are (1) to determine the chemical composition of the photochemical aerosols and (2) to measure the relative abundances of condensed organic gases forming the shells of the falling particles. The method consists in sampling the particles during the descent of the Probe. The method used for chemical analysis is Pyro-GC-MS technique in which the collected matter is heated in an oven and the produced pyrolysates are injected in a special inlet of the GCMS instrument (H. Nieman) of the Probe.