Authors: Kevin Zahnle, Luke Dones, & Harold F. Levison
Status: To appear in Icarus.
Abstract: We exploit recent theoretical advances toward a theory of the origin and orbital evolution of comets and asteroids to obtain revised estimates for cratering rates in the jovian system. We find that more than 90%, of the craters on the Galilean satellites are caused by the impact of Jupiter-family comets (JFCs). These are comets with short periods, in generally low-inclination orbits, whose dynamics are dominated by Jupiter. Nearly isotropic comets (long period and Halley-type) contribute at the 1-10% level. Trojan asteroids might also be important at the 1-10% level; if they are important, they would be especially important for smaller craters. Main belt asteroids are currently unimportant, as each 20 km crater made on Ganymede implies the disruption of a 200 km diameter parental asteroid, a destruction rate far beyond the resources of today's asteroid belt.
Twenty kilometer diameter craters are made by km-size impactors; such events occur on a Galilean satellite about once in a million years. The paucity of 20 km craters on Europa indicates that its surface is of order 10 Ma. Lightly cratered surfaces on Ganymede are nominally of order 0.5-1.0 Ga. The uncertainty in these estimates is about a factor of five. Callisto is old, probably more than 4 Ga. It is too heavily cratered to be accounted for by the current flux of JFCs. The lack of pronounced apex-antapex asymmetries on Ganymede may be compatible with crater equilibrium, but it is more easily understood as evidence for nonsynchronous rotation of an icy carapace.
Click here for an encapsulated postscript file of this paper. This paper contains color figures. Click here for an encapsulated postscript file containing only the color figures.
Click here for a pdf file of this paper.
Return to the Hal Levison's Homepage