Gravity Investigation to Characterize Enceladus’ 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 onboard 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-Frontier class mission. Numerical simulations are carried out to determine the gravity field in spherical harmonics to degree and order 30, and the Love number k2 and its phase. By combining Enceladus’ shape measured by Cassini and the geophysical constraints obtained through the processing of the simulated radio science data, we used a Bayesian inference network for the inversion of moon’s interior models. Our results indicate that the gravity investigation would enable tight constraints on core radius and density, ocean depth and density, and ice shell rigidity and viscosity. Further information on the hydrosphere properties might be gathered through optical navigation that would support the spacecraft orbit determination, leading to accurate measurements of Enceladus’ orientation model.