The Compositional Evolution of Icy Shells by Impact Processes

The composition of icy planetary surfaces is modified by impact processes. Impact gardening, melting, re-freezing and delivery of non-ice materials all influence the distribution of non-ice components in the shell. Impact processes depend strongly on the size of the impactors, and the random distribution of impacts across the surface will lead to heterogeneities in the composition of the ice. The distribution of non-ice components is important for understanding the effectiveness of melt probes, radar propagation, and other geophysical methods of determining the properties of the ice shell. Using the impactor size distribution inferred for the Jupiter system from cratering and dynamical studies, we model the evolution of the ice and non-ice (soluble and insoluble) components of the shell due to impact. Laboratory and model constrained ejecta, melt, and vapor distributions are used to redistribute the ice, soluble, and insoluble components of the shell after each impact, and the shell is allowed to evolve over different lengths of time. The resulting distribution of non-ice components will be analyzed to identify typical horizontal and depth scales of heterogeneity to inform the exploration of Europa and other icy bodies.