The Case for Future Gravity Science Investigations at Saturn with a Planetary Orbiter

The next phase in the robotic exploration of the Saturnian system will target unresolved questions about the gas giant's atmosphere, interior, magnetosphere, and rings that were left open by investigations on board the Cassini mission. Among these, we find gravity science objectives, which relate mainly to explaining the origin of the large wind-induced gravity signal and reconciling existing incongruities regarding the internal density distribution. Here we attempt to identify which future observations may yield additional information about Saturn's internal mechanisms. We report on the results of precise numerical simulations of a gravity science experiment carried out with a planetary orbiter in the 2040s and characterized by varying periapsis altitude over the 1 bar planetary surface. The goal is to identify achievable measurement requirements that can advance the current understanding of Saturn's interior and atmospheric dynamics. We find that inclined, elliptical orbits with low-altitude closest approaches over the northern hemisphere can improve the present determination of the gravity field coefficients by up to 1 order of magnitude, provided that at least a dozen pericenters are devoted to gravity science. Furthermore, if future observations are combined with the available Cassini Grand Finale data in the southern hemisphere, a significant improvement in terms of maximum measurable gravity field degree is observed.