Latitude variations of the polar caps on ganymede

Abstract

We have modeled Ganymede's polar regions as a frost layer overlying typical non-polar materials using a two-layer photometric model. The optical depth of the overlying layer is found to increase from a few tenths at the cap boundary to more than four at the poles. Such an increase is consistent with the predictions of Johnson's (1985) sputtering model but not with those of thermal migration models of the formation of Ganymede's polar caps. If the frost forms a distinct layer, it must be physically thin - on the order of millimeters or less - particularly near the cap boundary. Therefore, the mechanism responsible for its formation must be ongoing since impact gardening would destroy such a thin layer on short time scales. Interestingly, the photometric properties of the layer are similar to those of the surface of Europa. © 1996 Academic Press, Inc.