Tidal deformation of Ganymede: A parameter study in anticipation of future geodetic measurements

Abstract: Tidal Love numbers (h2 and k2) of a planetary body are dimensionless parameters describing its tidal response. For Ganymede, these parameters will be obtained during ESA's JUICE mission. Although Love numbers depend on its interior structure, it is not clear how precisely we can constrain Ganymede's interior structure. In anticipation of future measurements, we investigate the parameter dependence of tidal Love numbers of Ganymede considering a wide variety of calculation conditions. Our results indicate that Love numbers for Ganymede models without a subsurface ocean are not necessarily smaller than those with a subsurface ocean. The phase lag, however, depends primarily on the presence/absence of a subsurface ocean. Thus, the determination of the phase lag would be of importance to infer whether Ganymede possesses a subsurface ocean or not based only on geodetic measurements. Our results also indicate that the major control on Love numbers is the thickness of the ice shell if Ganymede possesses a subsurface ocean. This result, however, does not necessarily indicate that measurement of either of h2 or k2 alone is sufficient to estimate the shell thickness; while a thin shell leads to large h2 and k2 independent of parameters, a thick shell does not necessarily lead to small h2 and k2. We found that, to reduce the uncertainty in the shell thickness, constraining k2 in addition to h2 is necessary, highlighting the importance of collaborative analyses of topography and gravity field data.