Collisional interactions of ring particles: The ballistic transport process

As the erosion rate of the Saturnian rings resulting from meteoroid bombardment can be quite significant in the evolutionary history of the ring system, a simple model is constructed to study the relevant dynamics of ballistic transport of the impact ejecta. The combined process of collision with the ring plane particles, with the impact probability related to the optical depth and inelastic rebound from the ring plane until the random motion of the particle is effectively damped, is traced by using the Monte Carlo method. The numerical results indicate that the final distribution of the ejecta depends very much on the initial ejection velocity. For high-velocity fragments, their distribution tends to follow the optical depth variation of the rings. But for low-velocity fragments, pronounced edge effect with ejected particles accumulated at the boundaries of optical depth discontinuities could result. Therefore, in a global scale, the large increase of optical depth near the inner edge of the B ring, for example, as well as the depletion of micrometer-sized particles in the B ring and the Cassini division may be interpreted by the mechanism of ballistic transport. The edge effect found in the calculations might also be closely related to the formation of sharp edges and double peaks in a number of narrow ringlets. (The simultaneous operation of ballistic transport diffusion and gravitational resonant effects of satellites remains to be investigated.).