Collisional processes and transfer of mass among the planetary satellites

Several pairs of planetary satellites may have been involved, during the hi story of the Solar System, in mutual mass transfer processes. Such processe s can be triggered by catastrophic collisions of a satellite (parent body) with a third object. As a consequence, the collision fragments are injected into independent orbits that can cross the trajectory of the another satel lite (target). These swarms of secondary impacts may be of some importance influencing the properties of the target body. Even the formation of the at mosphere around some giant satellites may have been triggered by the gas re leased after the impacts of fragments onto the target's surface. Moreover, the different albedos and the different surface density of impact craters w ithin the same satellite system may be connected to peculiar collisional ph enomena, such as those we are dealing with. A quantitative modelling of the role of mass transfer processes obviously requires an estimate of how much material the parent bodies are able to supply, and under what circumstance s the process may take place. A general analysis of the various pairs throu ghout the major satellite systems present in the Solar System has been perf ormed in the present paper. Our analysis uses a statistical algorithm, comp uting, as a function of the initial properties of the fragments (masses and ejection velocities from their parent body), the mean intrinsic probabilit y of impact, and then the mean lifetime of a fragment before impacting the target, as well as the distribution of the relative velocity. For an order- of-magnitude estimate of the available amount of mass, some simple analytic al equations have been derived to evaluate the fraction of fragments from t he parent body that can reach the target. These formulae allow a preliminar y discrimination of the interesting cases. The pair Hyperion-Titan and the Uranus system have been analyzed in detail.