HR: 15:25h
AN: P43B-08    [Abstracts]
TI: Orbital Evolution of Impact Ejecta from some of the Biggest Craters on Saturn's Icy Satellites
AU: * Alvarellos, J
EM: alvarellos.jose@ssd.loral.com
AF: Space Systems/Loral, 3825 Fabian Way, MS L-27, Palo Alto, CA 94303 United States
AU: Dobrovolskis, A
EM: dobro@cosmic.arc.nasa.gov
AF: NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035 United States
AU: Zahnle, K
EM: Kevin.J.Zahnle@nasa.gov
AF: NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035 United States
AU: Hamill, P
EM: hamill@wind.sjsu.edu
AF: San Jose State Univ., Dept. of Physics, San Jose, CA 95192 United States
AB: We use the Swift numerical integration package written by Levison and Duncan (1994, Icarus 108, 18-36) to compute the orbital evolution of impact ejecta in the Saturn system. We consider four giant craters on three satellites: Herschel on Mimas, Odysseus and Penelope on Tethys, and Tirawa on Rhea. Ejection velocities and particle sizes are consistent with what is currently known about cratering physics. We consider impacts on competent surfaces (the spallation model of Melosh 1984, Icarus 59, 234-260) and into unconsolidated regolith (the gravity-scaling model of Housen et al. 1983, J.G.R. 88, 2485-2499). These two models should bracket the behavior of real impact ejecta. From each crater we launched 600 test particles according to each model at velocities comparable to or exceeding the satellite's escape speed. Most test particles are swept up by the source moon on time-scales of a few to several decades, and produce craters no larger than a few kilometers in diameter. A small but non-negligible fraction of material reaches satellites other than the source moon. Our models generate cratering patterns consistent with a planetocentric origin of most small impact craters on the Saturnian icy moons, but the predicted craters tend to be smaller than canonical Population II craters. We conclude that the known giant craters in the Saturnian system cannot account for the full range of observed Population II craters. A more complicated story, presumably one involving the disruption of co-orbital moons, is probably required to generate the larger Population II craters.
DE: 5420 Impact phenomena (includes cratering)
DE: 6022 Impact phenomena
DE: 6035 Orbital and rotational dynamics
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting