A Laboratory Model for Iron Snow in Planetary Cores

Abstract

Abstract Solidification of the cores of small planets and moons is thought to occur in the “iron snow” regime, in which iron crystals form near the core‐mantle boundary and fall until re‐melting at greater depth. The resulting buoyancy flux may sustain convection and dynamo action. This regime of crystallization is poorly understood. Here we present the first laboratory experiments designed to model iron snow. We find that solidification happens in a cyclic pattern, with intense solidification bursts separated by crystal‐free periods. This is explained by the necessity of reaching a finite amount of supercooling to re‐initiate crystallization once the crystals formed earlier have migrated away. When scaled to planetary cores, our results suggest that crystallization and the associated buoyancy flux would be strongly heterogeneous in time and space, which eventually impacts the time variability and geometry of the magnetic field.

Keywords

• crystallization
• core dynamics
• magnetic field
• dynamo
• snow