Inferring the structure and thermal state of Ganymede’s interior with tidal Love numbers and moment of inertia

ESA’s Jupiter Icy moons Explorer (Juice), equipped with a highly capable suite of geophysical instruments will accurately measure Ganymede’s tidal Love numbers k2 and h2 with the radio science experiment 3GM and the laser altimeter GALA during the low altitude orbital phase (GCO-500) (Van Hoolst et al. 2024).

As part of a prospective study for this upcoming exploration of Ganymede, we compute the moon’s tidal response across a wide range of interior structure models. Anelasticity is modeled with the Andrade rheology and several combinations of values of its parameters following the approach of Amorim and Gudkova (2025). Ganymede's hydrosphere is modeled using the equations of state of pure water and NaCl solutions with different concentrations following the SeaFreeze representation (Journaux et al. 2020). The ice shell is assumed to be either fully conductive or convective, depending on its thickness and viscosity assumptions. We systematically vary the thicknesses of the outer ice shell and hydrosphere, as well as the reference viscosity values of the ice shell and the high-pressure ice layer above the silicate mantle.

For each fixed hydrosphere configuration, we explore all possible structures of the silicate mantle and liquid core so that our models’ moment of inertia is within the acceptable range of values (Gomez Casajus et al. 2022). The influence of each parameter on the tidal Love numbers, as well as on the phase lags of k2 and h2, is analyzed. This approach aims to determine how measurements of these quantities by Juice can provide constraints on Ganymede's interior structure and thermal state.