Self-gravity wakes in Saturn's A ring measured by stellar occultations from Cassini

Abstract

An azimuthal brightness asymmetry in Saturn's A ring is caused by ephemeral agglomerations that continually form under the mutual gravity of the ring particles only to be torn apart by Keplerian shear. We calculate the shape and spacing of the self-gravity wakes from Cassini stellar occultations. The wakes are highly flatttened structures, with height/width ratio of 0.15 to 0.37, increasing outward across the A ring. The spacing between wakes increases with their height from a low value in the inner A ring of less than the wake width to >3 times the wake width in the outer third of the ring. The opacity of gaps between wakes also increases in the outer part of the ring where the wakes appear to be less coherent than in the inner and middle A ring. We calculate the vertical opacity of the A ring is 15-35% higher than previously reported.