Photochemical Enrichment of Deuterium in Titan's Atmosphere: new lights from Cassini-Huygens

Abstract : We reinvestigate a scenario initially proposed by Pinto et al. (1986) and Lunine et al. (1999), dealing with the photochemical enrichment of deuterium in the atmosphere of Titan, which is based on the possibility that the initial methane reservoir accessible to the atmosphere was larger than what is seen today, in light of the recent Cassini-Huygens measurements (Bézard et al. 2007). We show that this photochemical mechanism is not efficient enough in the atmosphere of Titan to explain its current D/H value, even if the current atmospheric reservoir of CH_4 is postulated to exist since 4.5 Gyr.