Determination of the Galilean Icy Satellites Internal Structure From Geodetic Measurements by Jupiter Icy Moons Orbiter

In the prospect of the JIMO mission, we design a protocol to determine the internal structure of the icy Galilean satellites, by means of geodetic measurements. In that purpose we analyze the influence of each single parameter of the internal structure on the tidal behavior of these bodies (change of shape, induced gravity field, tidal phase lag). The range of variation of each feature is defined from observational constraints, geodynamical modeling, and uncertainties on our knowledge of the physical properties of the materials involved in the models. Given a level of accuracy required on the measurements, this allows us to discriminate the features that can be unambiguously determined, from the one which will remain estimated with assumptions, and those for which geodetic measurements will not improve our level of knowledge. We also consider the information provided by other instruments possibly onboard JIMO (Radar, Remote sensing), complementarily to our approach. In application of these results, we present a program inverting simultaneously the Love numbers and tidal phase lag, based on a simulated annealing algorithm, and taking also into account constraints provided by other sources of information (observations and geodynamical modeling). This program has been designed in the prospect of the forthcoming measurement of Titan's gravity field by Cassini Radio Science Subsystems. Inversion of realistic test values for the Galilean satellites are presented as examples of application.