Fragmentation and exchanges during planetary core formation

Abstract eng:
Telluric planet formation involved the settling of large amounts of liquid iron coming from impactors into an ambient viscous magma ocean. Planetary initial state was largely determined by diffusive exchanges of heat and elements during this iron rain. Current models often assume that the metal rapidly equilibrated as drops of single capillary size settling at the Stokes velocity. But the dynamics is more complex, and influenced by the large viscosity ratio between the metal and ambient fluid. We study this two-phase flow using a model experiment, where a balloon of heated liquid metal is popped at the top of a tank filled with viscous liquid. We explore the relevant planetary regimes, including the whole range of viscosity ratios. High-speed videos allow determining the statistics of drop sizes, shapes, and velocities. Measures of the temperature decrease during settling allow defining a global turbulent diffusion coefficient, confronted to current analytical models.

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