New Constraints on Photochemical Enrichment of Deuterium in Titan's Atmosphere from Cassini-huygens Data

Daniel Cordier (1) , Olivier Mousis (2) , J. Lunine (3) , Audrey Moudens (4) , Véronique Vuitton (5)

1 ENSCR - Ecole Nationale Supérieure de Chimie de Rennes
2 Observatoire de Besançon
3 LPL - Lunar and Planetary Laboratory [Tucson]
4 IPR - Institut de Physique de Rennes
5 LPG - Laboratoire de Planétologie de Grenoble

Cassini-Huygens data are used to re-examine the potential sources of the D/H enhancement over solar, measured in methane, in Titan's atmosphere. Assuming that the system is closed with respect to carbon, the use of constraints from the Huygens probe for the determination of the current mass of atmospheric methane and the most up-to-date determination of D/H from Cassini/CIRS infrared spectra allow us to show that photochemical enrichment of deuterium is not sufficient to be the sole mechanism yielding the measured D/H value. A possible fractionation between CH3D and CH4 during the escape process may slightly enhance the deuterium enrichment, but is not sufficient to explain the observed D/H value over the range of escape values proposed in the literature. Hence, alternative mechanisms such as a primordial deuterium enrichment must be combined with the photochemical enrichment in Titan's atmosphere in order to explain its current D/H value.

Daniel Cordier, Olivier Mousis, J. Lunine, Audrey Moudens, Véronique Vuitton. New Constraints on Photochemical Enrichment of Deuterium in Titan's Atmosphere from Cassini-huygens Data. American Astronomical Society, 40th DPS meeting, Oct 2008, Ithaca, New York, United States. pp.31.07. ⟨insu-00361657⟩