Gravity Investigation to Characterize Enceladus's Ocean and Interior

A key objective for the future exploration of the icy moon Enceladus is the characterization of the habitable conditions in its internal ocean. Radio science instrumentation on board a spacecraft in a low-altitude orbit about Enceladus would enable gravity measurements that are fundamental to providing constraints on its internal structure. We present here the concept of operations and expected results of the gravity investigation for a New Frontiers-class mission. Numerical simulations are carried out to determine the gravity field in spherical harmonics to degree and order 30 and the Love number k 2 and its phase. By combining Enceladus's shape measured by Cassini and the geophysical constraints obtained through the processing of the simulated radio science data, a Bayesian inference network is used for the interior model inversion. Our results indicate that the gravity investigation would enable tight constraints on core radius and density, ocean depth and density, and ice shell rigidity. By assuming a high core rigidity and a preliminary modeling of dissipation in the ice shell, our interior model inversion also yields information on the ice shell viscosity. Further data on the hydrosphere properties might be gathered through optical navigation data by accurately measuring Enceladus's orientation model.