Dynamically depleted zones for Cassini's safe passage beyond Saturn's rings

Motivated by concern for the safety of the Cassini orbiter, we explore the orbital histories and reaccretion of circumplanetary particles in the Saturn lan system. Our goal is to find regions near the satellites that might be dynamically cleared of orbital debris. Including the gravitational effects of all the classical satellites out to Titan, we numerically integrate the orbits of test particles in the Saturnian system, examining the region from 2.4-24 R-S (Saturn radii), for 1000 years. Particles are followed until they impact a moon, enter the main ring, or travel well beyond Hyperion's orbit. Our numerical simulations demonstrate that the orbital eccentricities and inclinations of test particles are appreciably influenced only in the immediate neighborhoods of the satellites, and at the 2:1 and (to a much lesser degree) 3.1 resonances of Titan; the effects of a secular resonance appear just near Rhea. Simulations of material in Mimas' vicinity show that particles. whether launched from the satellite or placed in an originally uniform distribution across semimajor axis, are swept clear within a (theorrtically predicted) region where particle orbits eventually cross the satellite's; Mimas's orbital eccentricity broadens this sweep-up region. The timescale over which particles are removed by the satellites is of order a hundred years; the few members that remain in the cleared zone are identified as moving on stable horseshoe orbits. (C) 1998 Elsevier Science Ltd. All rights reserved.