Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23e..08s&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23E-08
Other
[6218] Planetary Sciences: Solar System Objects / Jovian Satellites, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites, [6290] Planetary Sciences: Solar System Objects / Uranian Satellites, [6299] Planetary Sciences: Solar System Objects / General Or Miscellaneous
Scientific paper
The icy satellites of the giant planets have a wide variety of compositions as indicated by their average densities. The compositions range from almost completely ice as in the case of Tethys to mostly silicate rock as in the case of Europa. The present knowledge about the structure and interior dynamics of these satellites, unfortunately, remains speculative. For the icy Galilean satellites, the Moment of Inertia (MoI) factors are well constrained but only under the assumption that the satellites are in hydrostatic equilibrium. Satellite Doppler-tracking data on the Saturnian satellite Rhea also allow constraints on its interior structure. Of these satellites, Ganymede and Europa are likely to be fully differentiated with water/ice outer layers, rocky mantles and iron cores. Callisto appears to be incompletely differentiated with an ice shell overlying an ice-rock core. Rhea is undifferentiated or partly differentiated. The water/ice shell of Europa is comparatively thin, about 150km thick. It is agreed to be mostly liquid water with an a few tens of kilometer thick ice lid. The water/ice layer on Ganymede should have a thickness of roughly 1/3 of the surface radius. It likely contains a liquid water ocean that stretches from a depth of some tens to a hundred kilometers to a depth of around two hundred kilometers. The depth extent of this ocean is, however, not well constrained and depends on the composition of the ice, and its heat transfer properties. Magnetic induction signals at Callisto suggest that this satellite also has an ocean similar to Ganymede. While the presence of oceans are relatively well understood for Europa and Ganymede from heat balance considerations and the water ice phase diagram understanding Callisto’s ocean is more challenging. In particular, considering its incomplete differentiation status. Little is yet known about the interior structure of Titan - for which sufficiently accurate gravity data are still not available - and Triton, the two other major satellites in the outer solar system and about the interior structure of the smaller satellites. Model calculations suggest that some of these satellites may also contain oceans. The depth to these oceans and their thicknesses can be estimated using heat transfer models and the phase diagram and material properties of water-ice including minor constituents like ammonia, methane, and salts. The dynamics of the interiors are speculated to be dominated by more or less sluggish convection underneath thick stagnant lids. These lids may keep the deep interior warm and frustrate ocean and even core freezing. While geophysical data on the gravity and magnetic fields are much wanted as constraints on the interior structure, laboratory data on the phase diagrams and transport properties (rheology, thermal conductivity) of ices are similarly needed for a better understanding of the state and the roles of the ice layers for the evolution of the satellites.
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