JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY

Important advances have recently been made in our understanding of the electromagnetic fields of Europa, Ganymede and Callisto. These developments have implications for the study of ion bombardment levels and patterns on satellite surfaces. For instance, the recently discovered magnetosphere of Ganymede would largely shield Ganymede's surface from the flux of energetic ions (trapped in the Jovian magnetosphere) which continually sweep by that moon. The distribution of ions to the surface would take into account those that accessed closed Ganymede field lines and those that entered a loss cone on Jovian field lines which are dragged over Ganymede's polar cap. This study proposes to map ion bombardment patterns on Europa, Ganymede and Callisto considering the fields created by and induced in these satellites. Individual particles are followed from a location upstream of a satellite to its surface using the superposed electromagnetic fields generated by Jupiter and the satellite. Charged particle measurements from the plasma and energetic particle detectors taken upstream of satellite surfaces will be used as inputs to the models. These inputs will include pitch-angle distributions and flux rates for protons, oxygen and sulfur. Likewise, observed significant decreases in corotational flow speeds as ions encounter Europa and Ganymede will be modeled as satellite electric potentials. These simulations will produce bombardment maps of satellite surfaces showing both the distribution of impacts and the associated flux levels over the surface. These results will estimate the rate of surface modifications by energetic charged particle bombardment. They will have important implications for the age of surface features and the nature of geologic processes. They will, for instance, give working models for assessing whether leading/trailing, polar/equator and other observed satellite surface asymmetries are related to the bombardment asymmetries of energetic ions. Such comparisons will be done for UV measurements from Galileo.