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Controversy has existed over whether or not viscous relaxation is an important process on the icy satellites. Previous models involved large extrapolations of Newtonian flow laws for ice, whereas ice is known to exhibit non‐Newtonian behavior. Recently, the flow law parameters for ice at the appropriate temperatures and stresses have been measured. Numerical modelling of the viscous relaxation of basins on Ganymede using these parameters has given implausibly short relaxation times. However, this model treated ice as a purely viscous substance, so that no elastic lithosphere could develop near the surface. Here we treat ice as a Maxwell visco‐elastic material and numerically model the relaxation of basins on Ganymede. We find that realistic Young's moduli lead to little relaxation occurring in basins even 4.0 Ga after their formation. Further, we demonstrate that within broad limits the near surface temperature gradient has little effect on this result. Finally, through examination of the distribution of Maxwell times in the vicinity of the crater, we show that most viscous relaxation occurs early in the basin's history when stresses are high, and thus Maxwell time is short. As stresses are relieved, the Maxwell time becomes long, and relaxation essentially ceases.

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A recent model of the origin of the Moon in a giant impact put forth by O'Neill [1991a and b] states that the bulk abundances of siderophile elements in the Moon would be provided by the impactor plus a late reduced veneer. A small Ni‐rich core would then separate setting the siderophile element abundance pattern in the lunar mantle. I test this hypothesis using simple mass balance and the results of an experimental study that I have conducted on the partitioning of moderately siderophile elements between basalt and Ni‐rich metal. I find this hypothesis to be viable under a limited set of conditions.