Convection and lithospheric strength in Dione, an icy satellite of Saturn

Abstract

Finite element numerical simulations for the structure of convection cells within a self-gravitating, Boussinesq fluid sphere with variable viscosity are used to determine temperature distribution, stream functions, velocities, and intensities of the stresses within Dione, an icy satellite of Saturn. A non-Newtonian, i.e., stress-dependent, viscosity is considered, but the numerical simulation, according to U. R. Christensen (1984a, Geophys. J. R. Astron. Soc. 77, 343–384), is carried out knowing that the properties of power law convection can be closely simulated by Newtonian flow with a reduced value of the activation enthalpy. The initial temperature profile has been determined taking into account the amount of energy trapped as heat during the accumulation process and the other energy source is the radioactivity of the long-lived isotopes. The obtained results seem to show a long duration endogenic activity in agreement with the geological observations. The intensities of the stress are able to fracture the icy crust both in extensional and in compressional regimes. The thickness of the mechanical lithosphere evolves in a way determined by the complex interplay of the lithospheric temperature gradient and the strain rate.