Dynamically Cleared Regions Beyond Saturn's Rings for Cassini's Safe Passage

J. A. Burns (Cornell Univ.), B. J. Gladman (Observatoire de Nice)

Concerned about the safety of the Cassini orbiter when it pierces the ring plane during its orbital tour, we explored the orbital histories and reaccretion of circumplanetary particles across inner regions of the Saturnian system. Our goal is to find locales just exterior to the rings that might be depleted dynamically of orbital debris. Using a regularized mixed variable symplectic integrator, we numerically computed the paths of test particles distributed uniformly between tex2html_wrap_inline13 (Saturn radii), for 1000 years. Our model included the gravitational effects of Saturn (up to tex2html_wrap_inline15 ) and all the classical satellites out to Titan. Particles were followed until they impacted a moon, entered the main ring, or traveled well beyond Hyperion's orbit.

The numerical simulations showed that the orbital eccentricities and inclinations of test particles were appreciably influenced only in the immediate neighborhoods of the satellites, as well as at the 2:1 and (to a much lesser degree) 3:1 resonances of Titan; effects of a secular resonance appear just near Rhea. Simulations of material in Mimas' vicinity find that particles, whether launched from the satellite or distributed uniformly across semimajor axis, are swept clear within a (theoretically predicted) region in which orbits eventually cross the satellite's; the nearby satellite's orbital eccentricity broadens this sweep-up region by imposing a forced eccentricity on the particles' orbits. Particles typically collide with satellites in about a hundred years. A few particles are trapped along stable horseshoe and tadpole orbits.