Dissociation of Methane Clathrate Hydrates and Cryovolcanism on Titan: Experimental Constraints.

Details Dissociation of Methane Clathrate Hydrates and Cryovolcanism on Titan: Experimental Constraints. Dissociation of Methane Clathrate Hydrates and Cryovolcanism on Titan: Experimental Constraints.

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p21d..06c&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P21D-06

Physics

6281 Titan

Scientific paper

In absence of any replenishment mechanism, the present-day atmospheric methane on Titan should be removed in a few tens of millions of years owing to UV-driven active photochemistry. Remote sensing observations by Cassini (Sotin et al. 2005, Lopes et al. 2007) and numerical models (Tobie et al. 2006) suggest that methane may be released during cryovolcanic events, from the dissociation of a subsurface clathrate reservoir. However, processes leading to clathrate dissociation at depth remain poorly understood, mainly because methane clathrates are very stable structures within the icy crust of Titan. High pressure - low temperature experiments have been conducted in order to investigate the variability of methane clathrate stability in Titan's conditions, using a sapphire-anvil cell cooled within a nitrogen cryostat. Three main factors may influence the stability of clathrates at depth: 1) the presence of ammonia in the icy crust and in the putative liquid layer; 2) the low amount of methane within the ice - possibly lower than the stochiometric value of the filled-cages clathrates structure; and 3) the antagonism between N2 and CH4 in the clathrate cages. In this work, a synthesis of the last three years of experimental and theoretical investigations of the ammonia effect on methane clathrates" stability will be proposed. In addition, it will be shown that experimental results concerning the effect of nitrogen and of the methane concentration relative to water are in good agreement with thermodynamic models. A low methane concentration decreases the dissociation temperature of structure I clathrates by more than 20-30 degrees, while the methane - nitrogen competition yields a shift that could reach 15 degrees. A combination of these two factors and the ammonia inhibition of methane clathrates is taken into account for providing new constraints on cryovolcanic processes within Titan.

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