Hyperion as a Dust Source in the Saturnian System

Abstract

It is argued that Hyperion, an irregularly shaped distant Saturn satellite, may act as a reasonably effective source of dust in the saturnian system. Several mechanisms (e.g., hypervelocity impacts of interplanetary grains or dust particles coming from the outermost saturnian moon Phoebe) should produce impact ejecta from Hyperion's surface, an appreciable share of which would escape into the planetocentric orbits initially close to that of Hyperion. Three forces of major importance influence the motion of the dust grains: Titan's gravity, solar radiation pressure, and plasma drag force. The first acting alone would lock the particles ejected at small initial speeds in a strong 4:3 mean motion resonance with Titan, so that they would form a stable dust belt around Hyperion's orbit. However, solar radiation pressure and especially plasma drag force effectively destroy the resonant locking in an interval ranging from one to several saturnian years for 10 to 100 μm-sized particles and at an even faster rate for smaller grains. Initial speeds of about 100 m sec−1and greater (measured at the boundary of Hyperion's action sphere) are also sufficient to unlock particles from the resonance stability zone. Once the resonance is broken, the orbits of dust particles become unstable and experience multiple close approaches to Titan. Eventually they can either collide with Titan, spread into the inner part of the saturnian system, or escape to the interplanetary space. Using numerical integrations, we performed a statistical study of the grain trajectories to determine the probabilities of various scenarios and to construct a relative distribution of dust in the Hyperion–Titan system. We found that most of the grains larger than ∼5μm will finally collide with Titan, smaller particles down to ∼1 to 2 μm will escape out of the system, and still smaller (submicrometer) particles will rapidly collide with Saturn. Of-order estimates of the dust influx to Titan are also made; they show that the upper limit of the income rate of the Hyperion particles is comparable with the direct influx of interplanetary grains.