Bottom-up Crystallization of Mercury’s Core

Abstract:

Knowledge of the composition, structure and physical properties of the materials in a planet’s interior is fundamental to understanding the evolution of the planet, and the environment from which it formed. Using ab-initio molecular dynamics we have studied the equation of state and thermodynamic properties of pure liquid iron at the conditions of Mercury’s deep interior. This work has paid particular attention to the effects of magnetism on the simulations, as changes in the magnetic moments of the atoms may affect the physical properties of iron. Initial results suggest a very gradual high to low spin transition in pure liquid iron, which is expected to remain predominantly in the high spin state throughout the conditions of Mercury’s core. We have determined thermodynamic properties such as the thermal expansion, Grüneisen parameter and constant volume specific heat directly from the calculations, such that we have also determined the adiabatic temperature gradient of pure liquid iron. This has been found to be lower than published melting curves [1,2] of iron suggesting bottom up crystallization in Mercury’s core.

References:

[1] Williams et al. (1987) Science, 10.1126/science.236.4798.181

[2] Alfè et al. (1999) Nature, 401: 462-464, 10.1038/46758