Frank Spahn

Impact-generated dust clouds around planetary satellites: spherically symmetric case

Abstract An analytic model of an impact-generated, steady-state, spherically symmetric dust cloud around an atmosphereless planetary satellite (or planet—Mercury, Pluto) is constructed. The projectiles are assumed to be interplanetary micrometeoroids. The model provides the expected mass, density, and velocity distributions of dust in the vicinities of parent bodies. Applications are made to Jupiters moon Ganymede and six outer satellites of Saturn. In the former case, the model is shown to be consistent with the measurements of the dust detector system onboard the Galileo spacecraft. In the latter case, estimates are given and recommendations are made for the planned experiment with the Cassini cosmic dust analyzer (CDA) during targeted flybys of the spacecraft with the moons. The best CDA pointing to maximize the number of detections is in the ram direction. With this pointing, measurements are possible within a few to about 20 min from the closest approach, with maximum minute impact rates ranging from about 1 for Phoebe and Hyperion to thousands for Enceladus. Detections of the ejecta clouds will still be likely if CDAs angular offset from the ram direction does not exceed 45°. The same model can be applied to dust measurements by other space missions, like New Horizons to Pluto or BepiColombo to Mercury.