HR: 14:10h
AN: P13F-03    [Abstracts]
TI: Thermal Evolution of Charon and the Major Satellites of Uranus: Constraints on Early Differentiation
AU: * Spohn, T
EM: tilman.spohn@dlr.de
AF: DLR Institute of Planetary Research, Rutherfordstrasse 2, Berlin, 12489, Germany
AU: Multhaup, K
EM: multhaup@uni-muenster.de
AF: Institute of Planetology, W. Klemmstrasse 10, Muenster, 48149, Germany
AB: A thermal history model developed for medium-sized icy satellites containing silicate rock at low volume fractions is applied to Charon and the satellites of Uranus Ariel, Umbriel, Titania, Oberon and Miranda. The model assumes homogeneously accreted satellites. To calculate the initial temperature profile we assume that infalling planetesimals deposit a fraction h of their kinetic energy as heat at the instantaneous surface of the growing satellites. The parameter h is varied between models. The model continuously checks for convectively unstable shells in the interior by updating the temperature profile and calculating the Rayleigh number and the temperature-dependent viscosity. The viscosity parameter values are taken as those of ice I although the satellites under consideration likely contain admixtures of lighter constituents. Their effects and those of rock on the viscosity are discussed. Convective heat transport is calculated assuming the stagnant lid model for strongly temperature dependent viscosity. In convectively stable regions heat transfer is by conduction with a temperature dependent thermal conductivity. Thermal evolution calculations considering radiogenic heating by the long-lived radiogenic isotopes of U, Th, and K suggest that Ariel, Umbriel, Titania, Oberon and Charon may have started to differentiate after a few hundred million years of evolution. With short-lived isotopes -- if present in sizeable concentrations -- this time will move earlier. Results for Miranda -- the smallest satellite of Uranus -– indicate that it never convected or differentiated if heated by the said long-lived isotopes only. Miranda's interior temperature was found to be not even close to the melting temperatures of reasonable mixtures of water and ammonia. This finding is in contrast to its heavily modified surface and supports theories that propose alternative heating mechanisms such as the decay of short-lived isotopes or early tidal heating.
DE: 5418 Heat flow
DE: 5430 Interiors (8147)
DE: 5455 Origin and evolution
DE: 6270 Pluto and satellites
DE: 6290 Uranian satellites
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting