Inside Jupiter's Galilean Satellites: Uncertainties Abound

Flybys of the Galilean satellites of Jupiter by the Galileo spacecraft revealed much about the interiors of the moons. For example, we know that Io, Europa, and Ganymede have large metallic cores, and that Callisto does not. We know that ice and rock are well separated in Europa and Ganymede but not in Callisto, and that Ganymede is the only one of the four moons with a magnetic field. We are fairly certain that Europa has an internal liquid water ocean, that Callisto probably has one too, and that Ganymede might have one. This presentation will discuss some of the major questions we still have about the interiors of these moons. For Io, we would like to know the thickness of the crust and lithosphere, the degree of partial melting in the mantle, and why there is no magnetic field. For Europa, the major unknown is the thickness of the ice crust above the liquid water ocean. Inferences about this from crater studies and theoretical models give ice shell thicknesses of tens of kilometers, while estimates from geologic indicators of nonsynchronous rotation and polar wander give ice shells only several kilometers thick. For Ganymede we need to ask if there really is a subsurface liquid water ocean and how the satellite generates its magnetic field. For Callisto, we are uncertain about the details of the ice-rock distribution with depth.