Single-sided shepherding

Narrow ringlets are observed to form at isolated Lindblad resonances in recent simulations (J. Hanninen and H. Sale, Icarus 108, 325-346 (1994) and 117, 435-438 (1995)), Our remarks are directed toward the interpretation of this phenomenon, Ringlet formation is a consequence of the negative angular momentum luminosity promoted by satellite perturbations of the streamlines of particle flow, Contraction halts once the surface density reaches a value such that the angular momentum luminosity vanishes, Our estimate for the formation time, t(f) similar to (M(p)/M(s))(1/2)Omega(-1), for low order resonances in optically thin rings is consistent with the results of the simulations, Ringlets drift across the width of resonance, W similar to (M(s)/M(p))(1/2)a, as a result of the unbalanced satellite torque, This occurs on the much longer timescale t(d) similar to (M(p)/M(s))Omega(-1) and cannot be observed in current simulations. (C) 1995 Academic Press, Inc.