Unusual origin, evolution and fate of icy ejecta from Hyperion

We readdress the idea that Hyperion may act as an effective source of dust in the outer Saturnian system. Hypervelocity impacts of dust particles comi ng from the outer irregular moons (Phoebe and several others recently disco vered) and., to less degree, bombardment by interplanetary micrometeoroids should eject surface material of Hyperion to planetocentric space. Unlike H yperion, whose motion is stabilized by a strong 4: 3 mean motion resonance with the neighbouring Titan, so that encounters with this satellite are pro hibited, a significant fraction of the Hyperion debris should be fast enoug h to be out of resonance. For slower ejecta, resonant locking may be destro yed later by the plasma drag and solar radiation pressure forces. The orbit s liberated from the resonance become unstable and experience multiple clos e approaches to Titan. Using numerical integrations, we performed a statist ical study of the grain trajectories to construct a spatial distribution of dust in the Hyperion-Titan system and to find out the eventual fate of the debris. Particles locked in resonance form an are-like structure along the Hyperion orbit centred on Hyperion's position, this "Hyperion swarm" is po pulated by grains of tens of micrometres in size and might be dense enough to be detected by the Cassini spacecraft during its flyby of Hyperion. The whole dust cloud in the Hyperion-Titan system is tilted off the equatorial plane of Saturn and has a structure that depends on the particle radii. No particular dust concentration in the vicinity of Titan was found. Most of t he grains larger than similar to 5 mum in size finally collide with Titan, whereas smaller particles are either lost in the inner part of the Saturnia n system or hit Saturn. Our estimates of the dust influx to Titan show that the incoming rate of Hyperion particles may exceed the direct influx of in terplanetary dust particles. The influx of icy (H2O) particles from Hyperio n might help to explain the observed abundance of CO and CO, molecules in T itan's atmosphere. (C) 2001 Elsevier Science Ltd. All rights reserved.