HST High-Resolution Backscatter Image of Saturn's G Ring

Abstract

On 14 October 1996, we imaged Saturn's faint G ring with the Hubble Space Telescope's WFPC2 Planetary Camera. This is the highest resolution image of the G ring ever obtained in backscattered light, with an image scale of only 282 km per pixel. The 400-s exposure was taken using the F555W filter at a solar phase angle of α=1.93° and a ring tilt of B=-3.82° as seen from Earth. The radial profile of the ring was derived from azimuthal averages of the ring brightness. It is highly asymmetric, with a sharp inner edge that is abrupt at the limit of our resolution, rising from 20 to 80% of maximum intensity over a distance of less than 700 km. Outward of its peak at r=169,000 km, the G ring brightness gradually diminishes over several thousand kilometers. From a high SNR profile, averaged over ring longitudes within 25° of the East (morning) ansa, the full-width at half-maximum intensity of the G ring is ∼5200 km; higher resolution, lower SNR, profiles suggest a somewhat smaller ring width. The similarities between the radial structure seen from the HST in backscatter, and the highest resolution Voyager 1 and 2 profiles obtained in forward scattered light, imply that dust and macroscopic particles have similar distributions within the G ring.