Gravity investigation of Saturn's inner system with the innovative Ring Skimmer concept

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 potentially sensitive to its tidal perturbations measured by the Love number k22, 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, visibility from Earth, 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, while the 3σ uncertainty derived for Mimas’s k2 is 0.02.