Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p13b0171m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P13B-0171
Other
5430 Interiors (8147), 5455 Origin And Evolution, 6280 Saturnian Satellites
Scientific paper
Measurements of the shape of Enceladus indicate that is is undifferentiated, yet several gigawatts of heat are being lost through the South Polar Terrain (SPT). Tidal heating of a region of lowered viscosity is a plausible power source, but before tidal heating can operate to maintain elevated temperatures, some other process must create an isolated region of low viscosity (since the heating does not appear to be a global phenomenon). A transient, regional differentiation episode may be the necessary trigger, and may even be sufficient to power the SPT outflows by itself (at least for a few million years). Such an event would likely lead to reorientation of Enceladus to place the SPT at the pole. This process is analyzed by calculating the evolution of the growth rate of gravitational (Rayleigh-Taylor) instabilities of different spatial scales (given by spherical harmonic degree) for a gradually warming, undifferentiated Enceladus including both radiogenic and tidal heat sources. Growth times for all modes are initially very long when the interior is cold, gradually decrease as the interior warms up, and then increase slowly again as radiogenic heating falls off on a billion year timescale. When the growth time for a given mode becomes short compared with the thermal evolution timescale (also about a billion years) then differentiation will proceed. We seek solutions for which the minimum growth time is comparable to the thermal evolution timescale. In this way, Enceladus can be caught in the act of differentiation, having had time for only a single, transient event of the appropriate scale (about 40 degrees in radius for the SPT). These constraints will narrow the range of acceptable heating rates and viscosity parameters (e.g. ice grain size) for the interior of Enceladus. The same models will also be computed for Mimas to demonstrate that under the same conditions, Enceladus is more likely to differentiate.
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