Impact Crater Formation on the Icy Galilean Satellites

Abstract

The possible existence of liquid water beneath the ice crusts of Ganymede and Europa makes these bodies of great scientific interest as the accessibility of the oceans has implications for astrobiology and future human exploration of the solar system. Study of the cratering trends on these bodies provides one means of assessing the depth of the ice layer above the subsurface oceans. This work combines observational and numerical modelling data to develop a quantitative model for impact cratering in pure H2O ice. Topographic profiles of craters on Ganymede are presented and used to construct scaling trends, which are then compared to similar trends for the Moon and Mars in order to assess differences in the cratering process in rock, ice and ice-rock mixes. The progression of central peak and central pit crater morphology as crater diameter increases, is used to develop a paradigm for central peak collapse and pit formation on Ganymede. These observed cratering trends are used to test the results of hydrocode simulation of impact cratering. These simulations were used to determine an appropriate material strength model, and its specific parameters, for the simulation of impact crater formation in un-layered ice. This optimal strength model is then applied to impact cratering in a layered ice and water target. The results from this numerical modelling are compared to the Europan cratering trends and used to estimate the thickness of Europa’s ice crust.