HR: 1340h
AN: P53A-1448    [Abstracts]
TI: The fate of methane clathrate hydrate within Titan
AU: Tobie, G
EM: gtobie@lpl.arizona.edu
AF: LPL, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721 United States
AU: Tobie, G
EM: gtobie@lpl.arizona.edu
AF: LPG, University of Nantes, 2, rue de la Houssiniere, Nantes, 44322 France
AU: * Lunine, J I
EM: gtobie@lpl.arizona.edu
AF: LPL, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721 United States
AU: Sotin, C
EM: sotin@chimie.univ-nantes.fr
AF: LPG, University of Nantes, 2, rue de la Houssiniere, Nantes, 44322 France
AB: Titan has a thick atmosphere composed primarily of nitrogen and methane. Methane is known to be irreversibly consumed photochemically on a timescale of a few tens of million years, which implies that any replenishment process must occur to maintain the methane abundance to its current value. Methane is believed to have been trapped within clathrate hydrate, a particular structure of ice, in Saturn's subnebula environnement, and then to have been incorporated within Titan's interior. Although the major part of clathrates is likely to have been devolatilized during the late stage of Titan's accretion, a significant portion could have "survived" within the deeper interior and could have been released later in Titan's history. Through coupled thermal and orbital calculations including a full description of the tidal dissipation, the heat transfer,the H$_2$O-NH$_3$ phase diagram and the methane clathrate stability, we study the possible evolution of clathrate distribution within Titan's interior, its effect of the thermal evolution, and the process of degassing from the interior. We show that only models with a few percent of ammonia and a significant fraction of methane clathrate within the interior can explain both the conservation of Titan's high eccentricity over the age of the solar system and the methane replenishment of the atmosphere. In our preferred scenario, two episodes of methane degassing are predicted: one during the first billion years and a second one after 3.5-4 Ga, explaining the present-day atmospheric methane abundance. Forthcoming data from the NASA/ESA Cassini-Huygens mission will allow us to test the present predictions.
DE: 5407 Atmospheres--evolution
DE: 5410 Composition
DE: 5430 Interiors (8147)
DE: 5455 Origin and evolution
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting