BALLISTIC TRANSPORT IN PLANETARY RING-SYSTEMS DUE TO PARTICLE EROSION MECHANISMS

Ballistic transport is the net radial transport of mass and angular momentum caused by exchanges of meteoroid impact ejecta. The detailed numerical simulations and analytic arguments in this paper demonstrate that many of the common morphological features in Saturn's A- and B-ring inner edge regions can be understood as products of ballistic transport. In particular, the sharp edges themselves are maintained at their present observed widths by a balance between sharpening by ballistic transport and broadening by viscous transport; and the nearly linear ramps in optical depth interior to the sharp edges are created by ballistic transport alone. Hump-like structures on the high optical depth side and undulations on both sides of the edge are also possible. We suggest that the observed 100-km undulatory structure in the inner B-ring arises through ballistic transport echoing of the inner edge. Features in the edge regions are generally well fit by using a strongly prograde ejecta distribution function, such as that of Cuzzi and Durisen (1990, Icarus 84, 467-501), combined with an inverse cube power-law ejecta speed distribution ranging from {less-than or approximate}2 m/sec up to {greater-than or approximate}70 m/sec. For plausible values of various uncertain input parameters, such as meteoroid influx rate, ring viscosity, and hypervelocity impact yield, we deduce ages for the inner edge features of 107 to 2 × 108 years. © 1992.