Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p12c..09s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P12C-09
Physics
5418 Heat Flow, 5770 Tidal Forces, 6218 Jovian Satellites, 6280 Saturnian Satellites
Scientific paper
It is well known that the eccentricity of Galilean satellites such as Io or Europa can lead to important values of tidal heating. The amount of tidal heating deposited in the different layers that compose such a satellite depends on the viscosity of these layers. For values of viscosity in agreement with laboratory experiments, this heating source can be up to two orders of magnitude larger than the heat produced by the decay of the radiogenic elements in the silicate fraction of the satellite. Heat is likely to be transferred by subsolidus convection through the outer ice I layer of Europa. We have carried out 2D thermal convection numerical models which include temperature dependent viscosity and heterogeneous tidal heating. Tidal heating is computed at each grid point and at each time step using the temperature/viscosity field. The amount of tidal heating limits the amount of heat which can be transferred at the lower thermal boundary layer. This amount can even be smaller than the heat flux due to the radiogenic decay in the silicate core. Numerical simulations suggest that the silicate core could eventually differentiate into a dense iron rich inner core and an iron-depleted silicate mantle very late in the history of the satellite (Some models predict that a liquid iron core formed only 500 My ago). In all cases, it prevents the satellite to freeze completely and suggest that an ocean would still be present at a 20 km depth. It can be noted that if tidal heating is not taken into account, a pure H2O ocean would freeze out in less than 200 My for reasonable values of viscosity. Applied to Titan, such a model (with the same viscosity law) suggests that the thickness of the outer ice I layer (or the depth of the ocean) is around 120 km. For values of viscosity in agreement with laboratory measurements, tidal heating can be maximum in the hot upwelling leading to partial melt at depth around 20 km. We are including damage equations and shear heating due to slip motion along the faults in the present models in order to investigate how faults, initiated by tidal stresses in the brittle outer layer, could propagate at depth and reach the area where ice is partially molten, and we compute. This may provide a reasonable process in order to explain the replenishment in CH4 of Titan's atmosphere.
Choblet Gaël
Sotin C. J.
Tobie Gabriel
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