On the survival of an internal liquid water reservoir at Enceladus' south pole

Details On the survival of an internal liquid water reservoir at Enceladus' south pole On the survival of an internal liquid water reservoir at Enceladus' south pole

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13f..03c&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P13F-03

Physics

[5418] Planetary Sciences: Solid Surface Planets / Heat Flow, [5422] Planetary Sciences: Solid Surface Planets / Ices, [5430] Planetary Sciences: Solid Surface Planets / Interiors

Scientific paper

The total heat power released at Enceladus' South pole is about 50 times larger than the available radiogenic power, implying that an additional source of energy exists. Tidal dissipation is the most likely candidate, but the observed power and its particular location at the south pole can be reproduced only if a liquid layer exists at depth (Tobie et al. Icarus 2008). Moreover, this liquid reservoir should spread over at least half of the southern hemisphere to induce sufficient tidal deformation at the pole. In order to determine the stability of this internal liquid reservoir and its effects on the dynamics of the overlying ice shell, we have developed a new tool that solves simultaneously mantle convection and tidal dissipation in 3D spherical geometry (Behounková et al. JGR, 2010). We also include in this new 3D technique the description of melt production and accumulation at the bottom of the ice shell. By systematically varying the orbital (eccentricity) and internal parameters (rheology, angular width of the deep liquid layer), we investigate the conditions under which the liquid reservoir could be stable. The nature of the viscous rheology for warm ice is found to play a major role on the thermal evolution of the ice shell, as it affects the optimal temperature at which a maximum tidal heating rate is produced. Whatever the rheology considered, the present day value of eccentricity does not induce sufficiently large amounts of tidal power to preserve a liquid layer. Nevertheless, when larger values of the eccentricity are considered (typically several times the present day value), possibly corresponding to earlier states in Enceladus' recent past, significant tidal power is produced for a sufficiently large ocean width (larger than 60°): in this case, large amounts of melt are obtained for reservoirs covering more than 120° around the south pole. However, the competing freezing effect caused by efficient convective heat loss can lead to ocean crystallization in a few million years if tidal heat production is not large enough. We show that this effect is overcome for ocean widths larger or equal to 180° if the eccentricity is at least 4 times the present day value. In this case, the survival of the liquid reservoir is the rule rather than the exception.

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