Numerical simulations of the thermo-chemical evolution of the cores of Ganymede and Europa and implications for magnetic field generation in terrestrial planets

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One of the most compelling discoveries of the Galileo mission was the detection of a selfsustained magnetic field at Jupiter’s moon Ganymede. In the present project, the thermochemical evolution and the magnetic field history of Ganymede will be modelled using parameterized convection, a thermodynamic description of core processes driving the dynamo, and dynamo models of cores with iron snowfall and iron-sulfide flotation. The aim is to understand how parameters such as core composition and mantle rheology would constrain core convection (thermal or compositional) and dynamo action in the core and to come up with an explanation for the magnetic field of Ganymede. At the same time we need to provide an explanation why a field is lacking on Europa. Recent experimental data on the Fe-FeS system suggest that the dynamo in Ganymede may be compositionally driven but that it may function substantially different than the geodynamo. In the latter, an inner core grows from below driving convection in the core and the dynamo. In Ganymede (and in Europa) the core may freeze via precipitation and the fall of Fe snow and/or through the floating of FeS flakes. This may occur in cores sufficiently close to the eutectic composition in sufficiently small planets and satellites. We will discuss the application of the model to other planets such as Mars.