The rings of Uranus - Results of the 10 April 1978 occultation

Abstract

Observations of the 10 Apri11978 stellar occultation by the rings of Uranus are presented. Nine rings were observed and their radii and widths are caiculated. Rings ' TJ, y, and {j are found to be most likely circular and coplanar, in agreement with previous analyses; the remaining rings are either noncircular or slightly inclined. The width of the E ring is a linear function of its radius from the center of Uranus, projected onto the satellites' orbital plane; this suggests that it forms one continuous noncircular ring. The optical depth profile of the E ring has not chl;lnged significantly since March 1977. A model of this ring which fits all available observations adequately is that of a uniformly precessing Keplerian ellipse coplanar with the satellites' orbits. This model permits predictions of the radius and width of the E ring for future occultations. The precession rate is used to determine J 2 for Uranus, on the assumption that precession is caused solely by the planetary oblateness and not by satellite-ring interactions.