Edgington, AL; (2016) The Structure, Composition and Evolution of Mercury's Core. Doctoral thesis , UCL (University College London).

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Abstract

This thesis presents the results of ab initio molecular dynamics calculations of the adiabatic gradient of pure liquid iron and a liquid Fe-S-Si mixture with the relative atomic percentages, 80:10:10. Laser-heated diamond-anvil-cell experiments have been conducted to measure the liquidus and solidus relationships of Fe0.8S0.1Si0.1. First-principles molecular dynamics is combined with thermodynamic integration and free-energy minimisation to simulate the spin transition in pure liquid iron and liquid Fe0.8S0.1Si0.1. From the magnetic transition, the equations of state, thermodynamic properties and adiabatic gradients of pure liquid iron and liquid Fe0.8S0.1Si0.1 are determined. The calculated adiabatic gradients are used alongside the gradients of published melting curves of iron and the measured liquidus of Fe0.8S0.1Si0.1 to provide insight into the crystallisation regime of the core of Mercury. The suggested crystallisation regime of a hypothetical pure iron or Fe0.8S0.1Si0.1 Mercurian core depends strongly on the derivative of the melting curve. Results suggest that a Fe0.8S0.1Si0.1 core of Mercury may start in a ‘top-down’ crystallisation regime resulting in a complex core structure with a possible stratified Fe-S layer at the top of the core, which, may in-part explain the observed weak magnetic field of Mercury.

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