Gravity Investigation of Saturn’s Inner System with the Innovative Skimmer Concept

Abstract

Abstract We present an in-depth feasibility study of innovative gravity science measurements of Saturn’s inner system, which explores the different regions of the rings, the innermost moons, and the planet itself. The study is enabled by the novel Skimmer concept, where the spacecraft grazes repeatedly the rings over multiple passes. Because of the spacecraft’s proximity to the rings, the experiment allows for the determination of their radial density distribution with unprecedented accuracy. These observations are especially important for the B and F rings, whose masses are not well constrained. During the closest approaches to Saturn, the spacecraft is sensitive to its tidal perturbations measured by the Love number k 22, which holds key information about the interior structure of the planet. The orbit geometry also allows for close flybys of icy moons not explored by the Cassini mission from a gravity perspective. Specifically, we focus on the measurements of Mimas’s tidal perturbations, indicative of the presence of a submerged ocean under the icy surface. We perform precise numerical simulations of the gravity experiment and provide an account of the expected accuracies by means of a covariance analysis. The results are based on two trajectories of the Skimmer class which differ by altitude over the rings, proximity to Saturn, and number of passes. We find that the masses of the outer-ring regions are determined to better than 0.10 Mimas masses, with the case consisting of fewer but closer ring overflights generally yielding better accuracies. The 3σ uncertainty derived for Mimas’s k 2 is 0.02, after six close equatorial flybys.