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O. Mousis (Obs. Paris, University of Nantes), D. Gautier (Obs. Paris), D. Bockelée-Morvan (Obs. Paris), B. Dubrulle (CEA Saclay), F. Hersant (Obs. Paris and CEA Saclay)
The hydrodynamic collapse occuring in the last phase of the formation of Saturn generates a subnebula in which the regular satellites of the planet were presumably formed (Coradini et al., 1995, Surveys in Geophysics, 16, 553) We have elaborated a turbulent model of this subnebula derived from the solar nebula model of Dubrulle (1993, Icarus, 106, 59). We demonstrate that CO and N2 were not converted into CH4 and NH3 in the subnebula, except quite close to Saturn, where the amount of matter was too small to form Titan. Most of the mass of the subnebula is in the cold outer region, implying that planetesimals which formed Titan originated from this region and subsequently migrated inwards. The solar nebula contained some amount of NH3 and CH4 vaporized from ices infalling from the presolar cloud. When the nebula cooled down, these molecules were trapped in the form of hydrates or clathrate hydrates in planetesimals contained in the feeding zone of Saturn. These planetesimals did not vaporize when entering into the cold outer part of the subnebula. Under the assumption that CH4 in the atmosphere of Titan, which is continuously photolysed by the solar radiation, is replenished by outgassing from the interior of the satellite, we may reproduce the amount of atmospheric CH4 and its D/H ratio. The fit of the D/H ratio in Titan then permits us to evaluate the deuterium enrichment in methane ices which fell from the presolar cloud onto the nebula discoid.
The author(s) of this abstract have provided an email address for comments about the abstract: Olivier.Mousis@chimie.univ-nantes.fr