Voyager observations of the color of Saturn's rings

Abstract

Previously unreduced high-resolution Voyager 2 images of Saturn's main rings are used to generate reflectivity (I/F) profiles as a function of radius. Ratios of profiles taken from green, violet, orange, and UV filter images are then produced. The I/F ratios are a diagnostic of composition and provide us with information on the rings' present state of compositional evolution. The rings are extremely reddish in color which suggests that they could not be pure water ice. In addition, we find that the C ring and Cassini division are, in fact, less red or more neutral in color than the A and B rings. This is contrary to the impression given by the familiar enhanced Voyager color images which represent them falsely as bluish in color. The most likely candidate for the non-icy components are silicates and organics. The sources of these pollutants are of extreme importance in determining the compositional history of the rings. The radial profiles of ring color ratio exhibit several very interesting properties; (a) broad-scale, fairly smooth, color variations which are only weakly correlated with underlying ring structure (optical depth variations) across the outer C ring and inner B rings as well as the Cassini division region; these variations are probably consistent with ballistic transport; (b) fine-scale, noise-like (but unquestionably real) color variations across at least the outer two-thirds of the B ring. Not only the "redness" but also the spectral shape varies. These variations are currently unexplained. Ground-based spectroscopic observations should be pursued to study the implied compositional heterogeneities on at least the larger scales. This data set will be used for modeling of the color and composition of the main rings using ballistic transport and radiative transfer theories. We have provided true and false color visualizations of the rings generated from the one-dimensional (I/F) profiles and color ratios, respectively. The overall color of the rings is an extremely pale tan, and subtle color variations in the B ring are evident to the unaided eye upon careful inspection. © 1996 Academic Press, Inc.