Upper Limit on the Sizes of Shepherding Satellites at Saturn's Ring G

摘要

An accurate analytical theory of the absorption of energetic magnetospheric particles by an inert satellite is developed for the case in which the radius b of the satellite is much less than the equatorial gyroradius r sub g of the particles and in which r sub g is in turn much less than the radius r of the satellite's orbit. In previous interpretations of Pioneer 11 observations an estimations an estimate of the lifetime against absorption of energetic protons (E > 80 MeV) at Saturn's ring G has been made. This lifetime is used in the framework of the absorption theory to establish an upper limit on the sizes of shepherding satellites associated with the ring. The resulting upper limit, ignoring the absorption of the optically observed particulate matter, is sum from i=1 to N of (b sub I) = 6 sq km (uncertain by a factor of 2) for an assemblage of N satellites of various radii sub i. It is noted that ring G lies outside the Roche limit. No shepherding satellites at ring G were detected optically by Voyagers 1 and 2, though the lower limit of sensitivity of this technique was b about 10 km for an albedo exceeding 0.1 and the searches were not comprehensive in lognitudinal coverage. (Reprints).