Rotational Dynamics of Icy Satellites : Tidal response and forced longitudinal librations at the surface of a viscoelastic Europa

Abstract

The icy satellites of the giant planets Jupiter and Saturn are among the most interesting celestial bodies in our Solar System. The interpretation of various remote sensing observations performed by the Voyager, Galileo and Cassini-Huygens missions strongly suggests that many icy satellites harbor a subsurface water ocean underneath the ice shell covering the satellites. Since the availability of liquid water is one of the prerequisites for the origin and evolution of life as we know it, the characterization of the physical properties of the putative subsurface oceans (and the overlying ice shells) has become a key research topic in planetary sciences. Due to the unavailability of direct means to explore these internal oceans, the relevant physical properties of the interior need to be derived from the combined interpretation of remote sensing measurements of observables such as the strength of the induced magnetic field, the amplitude of tidal deformations, the strength of gravity perturbations due to tides and the amplitude of forced longitudinal librations. This dissertation concentrates on the development of a unified and self-consistent physical model to determine the tidal and rotational response of a viscoelastic icy satellite with an internal water ocean. The developed tidal-rotational model is then applied to analyze the relation between the aforementioned observables (with the exception of the induced magnetic field) and the physical properties that characterize the internal structure of an icy satellite. The results in this thesis strongly suggest that the measurement of the libration amplitude of Europa’s shell with an accuracy of a few meters has the potential to provide a reasonable constraint on the rigidity of the ice-I shell in combination with measurements of the tidal response (Love numbers) at the surface. However, the modelling presented here is not extensive enough to support a strong conclusion regarding whether the ice shell thickness could be inferred from combined measurements of the libration amplitude and tidal Love numbers at the surface of Europa.