Thermal evolution of the Galilean moons’ embryons during their accretion phase

The extent of differentiation of the Galilean moons interiors is still not well assessed. The moments of inertia of Callisto retrieved from Galileo’s gravity data suggest that its structure is not fully differentiated. Also, a recent reanalysis of the Galileo data questions the very existence of Europa’s metallic core postulated since decades. Here we aim at understanding the accretion conditions of the Galilean moons that would enable them to grow free of global melting and differentiation. To do so, we use a numerical model that mimics the thermal evolution of the interiors of icy moons during their accretion and post accretion phases. Each moon’s embryo experiences tidal heating, radiogenic heating, accretional heating due to multiple impacts and heating from the ambient environment circumplanetary disk during its growth. The extent of each considered heating process depends on the assumed formation path of each moon within the Jovian circumplanetary disk. We thus explore the best-case scenarios explaining a Callisto-like moon that is partially differentiated, and a Ganymede-like moon that is fully differentiated. The case of a Europa is also investigated, and specifically the conditions enabling the melting of iron and the formation of a metallic core.