Can Europa's obliquity help probe its interior structure?

Jupiter's icy moon Europa is currently seen as the most habitable world closest to Earth. Data from the space mission Galileo supported the presence of a global subsurface water ocean in direct contact with a rocky mantle, implying possible rock-water processes similar to those occurring on Earth's ocean floor, which is teeming with life. Although Juno can provide occasional glimpses of the Galilean satellites, close-up observations are not expected until the arrival of Europa Clipper and JUICE in the Jovian system. In the meantime, radar astronomy can help expand our understanding of this intriguing ocean world.

There are ongoing efforts to determine Europa's obliquity from radar echoes observed with the Goldstone Solar System Radar and the Green Bank Telescope [1]. In this contribution, we will present our latest models for icy moon obliquity and nutations, and demonstrate the need for precise modelling of elastic deformation in the ice shell. We will also investigate possible resonant amplification of the obliquity due to ocean dynamics.

This work is financially supported by the Belgian Science Policy Office (BELSPO) through the BRAIN.be-2.0 programme.

[1] Margot J.-L., Spin states of Europa and Ganymede, European Geosciences Union General Assembly 2025