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The long-term stability of a possible aqueous ammonium sulfate ocean inside Titan |
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| Authors: | PM Grindrod AD Fortes DL Feltham L Vo?adlo |
| Institution: | a Centre for Planetary Sciences, Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK b Department of Earth and Planetary Sciences, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064-1077, USA c Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK |
| Abstract: | We model the thermal evolution of a subsurface ocean of aqueous ammonium sulfate inside Titan using a parameterized convection scheme. The cooling and crystallization of such an ocean depends on its heat flux balance, and is governed by the pressure-dependent melting temperatures at the top and bottom of the ocean. Using recent observations and previous experimental data, we present a nominal model which predicts the thickness of the ocean throughout the evolution of Titan; after 4.5 Ga we expect an aqueous ammonium sulfate ocean 56 km thick, overlain by a thick (176 km) heterogeneous crust of methane clathrate, ice I and ammonium sulfate. Underplating of the crust by ice I will give rise to compositional diapirs that are capable of rising through the crust and providing a mechanism for cryovolcanism at the surface. We have conducted a parameter space survey to account for possible variations in the nominal model, and find that for a wide range of plausible conditions, an ocean of aqueous ammonium sulfate can survive to the present day, which is consistent with the recent observations of Titan's spin state from Cassini radar data Lorenz, R.D., Stiles, B.W., Kirk, R.L., Allison, M.D., del Marmo, P.P., Iess, L., Lunine, J.I., Ostro, S.J., Hensley, S., 2008. Science 319, 1649-1651]. |
| Keywords: | Titan Ices Interiors Thermal histories Astrobiology |
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