Convection in the subsurface ocean of icy moons and response of the upper ice layer

The main reservoirs of liquid water in the Solar System are hidden beneath the icy shells of some of the “icy moons” orbiting the gas giants Jupiter and Saturn. Although these moons lie well outside the traditional habitable zone, tidal forces exerted by their parent planet and internal radiogenic heating can sustain subsurface oceans of liquid water. These environments may offer the necessary conditions for life, making icy moons key targets in the search for extraterrestrial biospheres. Unfortunately, direct exploration of these oceans remains out of reach by current space mission technology, which is limited to surface observations. However, surface activity observed on several of these moons suggests that internal processes may be coupled with surface dynamics, potentially enabling surface-subsurface interactions. Previous global models have shown that large-scale fluid motions within the oceans may lead to latitude-dependent variations in heat flux at the ice-ocean boundary. In this study, we investigate intermediate-scale, localized convective dynamics within the subsurface oceans of icy moons, showing that these oceans can be dominated by intense thermal convection which can generate differential heat fluxes and local interactions at the ice-water interface. To explore this issue, we numerically integrate a simplified turbulent convective fluid model, coupled with a linear approximation for the freeze-melt processes of the overtopping ice layer. We observe that the resulting spatial variability in basal melting and freezing rates could induce thickness variations of the ice shell. These predictions can be tested by upcoming missions such as ESA's JUpiter ICy moons Explorer through gravity and altimetry measurements, offering new insights into the physical coupling between surface and interior also at small spatial scales.