MSC Seminar. 20/01/2025. Michael Le Bars (IRPHE, Marseille): “Iron snow in planetary interiors”

The surprising magnetic fields observed in some small celestial bodies, such as Mercury and Ganymede, may be attributed to “iron snow” resulting from the top-down solidification of their otherwise stably stratified liquid cores. This complex dynamic combines phase-changing, two-phase flows with buoyancy effects. Its modeling has, until now, been oversimplified, schematically assuming a constant flux of buoyancy in both space and time, associated with the remelting of uniform-sized crystals at the bottom of a motionless, stably stratified snow zone. By combining laboratory analog experiments and idealized numerical simulations, we further investigate the fluid motions that could lead to dynamo action. In particular, we highlight the role of supercooling and the two-way coupling between flakes and flows, which result in a wide distribution of flake sizes and contribute to a dynamic that is episodic in time and heterogeneous in space.