Abstract DGP2026-52

The icy moons of Jupiter have become prime targets for upcoming planetary missions such as JUICE and Europa Clipper, largely because their subsurface oceans may host habitable environments (Van Hoolst et al., 2024). Among these moons, Ganymede stands out, not just as the largest moon in the Solar System, but as the only moon that possesses an intrinsic magnetic field (Kivelson et al., 2004). JUICE will spend three years performing multiple flybys of the Galilean moons before entering the orbit around Ganymede in 2034. During this orbital phase, the spacecraft will acquire global topography with the GALA instrument (Hussmann et al., 2025) and determine Ganymede’s gravity field to approximately degree and order 40 (De Marchi et al., 2021).

In this study, we explore the thermal and dynamical evolution of Ganymede’s rocky interior using the geodynamical code GAIA (Hüttig et al., 2013). The thickness of the silicate mantle is varied between 840 km and 1304 km, consistent with interior structure estimates (Rückriemen et al., 2018). Our models use a pressure and temperature-dependent viscosity following an Arrhenius law (Hirth & Kohlstedt, 2003), core cooling and the decay of radioactive heat sources. Because both radiogenic heating and mantle rheology strongly influence the interior’s convective behavior and long‑term cooling, we test a range of U, Th, and K abundances. To capture the contrast between hydrated and dry mantle conditions, the reference viscosity is varied between 1018 Pa s and 1020 .

We test the effects of magmatism on the interior evolution by considering partial melting in the silicate layer and instantaneous melt extraction. Since magmatism affects the thermal evolution of the interior, we vary the extrusive to intrusive ratio. We investigate models where the entire amount of melt produced in the interior is extracted to the surface and models where the melt remains trapped in the subsurface beneath the ocean floor at depths between 30-200 km. 

We find that models with efficient extrusion cool Ganymede’s interior more rapidly during the early evolution, yet present‑day average mantle temperatures converge to 1200–1250 K, depending on the assumed intrusion depth. Scenarios with highly efficient melt extraction produce a thicker lithosphere, which in turn insulates the deeper interior and results in elevated core–mantle boundary (CMB) temperatures. Although earlier work allows for a transient early thermal dynamo, the persistently sub‑adiabatic CMB heat fluxes in our simulations imply that a purely thermal dynamo was never viable throughout Ganymede’s evolution.

The heat transport in the rocky mantle is critical for the core temperature and CMB heat flux, both important parameters for magnetic field generation. In addition, we calculate the mass anomalies associated with the density variations predicted by our simulations and compare them with those inferred from Galileo Radio Doppler measurements (Palguta et al., 2006). Together, these models provide a valuable framework for interpreting Ganymede’s internal evolution and will support the scientific return of JUICE by informing data analysis and contextualizing future observations.