Compositional control on impact crater formation on mid-sized planetary bodies: Dawn at Ceres and Vesta, Cassini at Saturn

High-resolution mapping of Ceres, Vesta and the icy satellites Saturn, Uranus Pluto reveals a rich variety well-preserved impact crater morphologies on these low gravity bodies. These objects provide natural laboratory to study effects composition formation processes under similar surface conditions (though mean velocities vary by several factors). Simple craters occur all bodies but subtle differences in morphology Ceres are recognized. Immature complex (with large floor mounds not terraces or conical central peaks) while smaller than predicted consistent with its silicate composition. Asymmetric simple incomplete scarp development) likely related differential overburden stresses rim, their occurrence is lower crustal strength including Ceres. mature exhibit increasing degrees complexity, spiral deformation patterns (related failure converging material), peaks, melt. Cerean morphologic types simple-complex transition diameters those satellites, indicating much weaker rheology for Ceres' outer layers conditions. geophysical indications low-density water ice probably clathrate shell. Fluidized deposits (impact melt melt-solid mixtures) significant >25 km across absent Saturn satellites. Central pit common (at ~75 150 scaling from larger Galilean satellites) Saturnian Charon. The contrasting behaviors Saturn's moons contrary expectation given higher at might be internal temperatures, fraction non-ice material correlation near ?0.65 rather ?1, perhaps due increased porosity fundamental similarity however, indicates that results even if non-(ice+clathrate) components as high ~30 vol%.