A non-equilibrium slurry model for planetary cores with application to Earth’s F-layer

Slurry regions may exist in the cores of several terrestrial bodies and are expected to influence the dynamics of deep planetary interiors and the viability of maintaining global magnetic fields. Here, we develop a two-component slurry model of the lowermost outer core of the Earth (the F-layer). In contrast to most previous models of slurries in planetary cores, we explicitly model the physics controlling the nucleation, growth and sinking of individual iron crystals and do not assume that the layer is in phase equilibrium. We assume that falling crystals do not interact and that the temperature and the overall composition are imposed, which allows us to solve for the volume fraction of solid in the layer and the size distribution of crystals. Models that produce a plausible heat budget and density excess compared with the bulk core yield a solid fraction that is far below that predicted by phase equilibrium and have a crystal size distribution dominated by the smallest particles with a maximum particle radii of 3 cm. The model can be used to understand the role of non-equilibrium effects in other planetary cores.