Title:
Bombardment of the regular satellites of Jupiter and Uranus during an episode of giant planet migration

Abstract:
The major satellites of the outer planets are some of the most heavily cratered bodies in the solar system. Crater counting combined with chronology models is one of the most powerful tools known to date the ancient surfaces of many solar system objects. Combined with age measurements of samples obtained from such bodies allows for obtaining absolute ages rather than only relative values. Thus far the only two bodies for which this has been accomplished are the Moon and Mars. For the outer solar system, no such connection be made, but inferred crater densities can be linked to those of the Moon and Mars via dynamical models, which subsequently allow for the computation of surface ages.

Here we report on dynamical experiments wherein we calculate predicted crater densities on the two largest Galilean satellites of Jupiter and the major Uranian satellites during an episode of late giant planet migration. For the Uranian system, we obtain crater densities that are a little lower than those on the lunar highlands, suggesting little crustal melting during and after giant planet migration. We reach a similar conclusion for the Galileans. This implies that the surface ages of Ganymede, Callisto and the Uranian satellites are at least as old as the epoch at which the giant planets migrated.