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The Astrophysical Journal 752 (2012) 125
Titan's Bulk Composition Constrained by Cassini-Huygens: Implication for Internal Outgassing
G. Tobie 1, D. Gautier 2, 3, F. Hersant 4, 5, 6, 7

In the present report, by using a series of data gathered by the Cassini-Huygens mission, we constrain the bulk content of Titan's interior for various gas species (CH4, CO2, CO, NH3, H2S, Ar, Ne, Xe), and we show that most of the gas compounds (except H2S and Xe) initially incorporated within Titan are likely stored dissolved in the subsurface water ocean. CO2 is likely to be the most abundant gas species (up to 3% of Titan's total mass), while ammonia should not exceed 1.5 wt%. We predict that only a moderate fraction of CH4, CO2, and CO should be incorporated in the crust in the form of clathrate hydrates. By contrast, most of the H2S and Xe should be incorporated at the base of the subsurface ocean, in the form of heavy clathrate hydrates within the high-pressure ice layer. Moreover, we show that the rocky phase of Titan, assuming a composition similar to CI carbonaceous chondrites, is a likely source for the noble gas isotopes (40Ar, 36Ar, 22Ne) that have been detected in the atmosphere. A chondritic core may also potentially contribute to the methane inventory. Our calculations show that a moderate outgassing of methane containing traces of neon and argon from the subsurface ocean would be sufficient to explain the abundance estimated by the Gas Chromatograph Mass Spectrometer. The extraction process, implying partial clathration in the ice layers and exsolvation from the water ocean, may explain why the 22Ne/36Ar ratio in Titan's atmosphere appears higher than the ratio in carbonaceous chondrites.
1 :  Laboratoire de Planétologie et Géodynamique de Nantes (LPGN)
CNRS : UMR6112 – INSU – Université de Nantes
2 :  Observatoire de Paris - Site de Paris (OP)
CNRS – INSU – Observatoire de Paris
3 :  Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA)
CNRS : UMR8109 – INSU – Observatoire de Paris – Université Pierre et Marie Curie (UPMC) - Paris VI – Université Paris VII - Paris Diderot
4 :  Observatoire aquitain des sciences de l'univers (OASU)
CNRS : UMS2567 – INSU – Université Sciences et Technologies - Bordeaux I
5 :  Laboratoire d'Astrophysique de Bordeaux (LAB)
CNRS : UMR5804 – INSU – Université Sciences et Technologies - Bordeaux I
6 :  Université Sciences et Technologies - Bordeaux 1
Université Sciences et Technologies - Bordeaux I
7 :  Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB)
CNRS : UMR5804 – INSU – Université Sciences et Technologies - Bordeaux I
Planète et Univers/Astrophysique/Astrophysique stellaire et solaire

Physique/Astrophysique/Astrophysique stellaire et solaire
planets and satellites: atmospheres – planets and satellites: interiors