Geochemical studies of the cores of terrestrial planetary bodies

Abstract

From the Earth to asteroids, numerous rocky bodies in our solar system are believed to have a metallic core at their center. However, due to the inaccessibility of these cores, fundamental issues, such as the composition of the cores or the processes of core formation and core evolution, are not well known. I have conducted both theoretical and experimental geochemical studies which have improved our understanding of the cores of terrestrial planetary bodies. The radioactive decay of K is an important planetary heat source, but the distribution of K in terrestrial planetary bodies has been debated. My experimental work, which examined the solubility of K in metal, shows no evidence for K to be an important heat source in metallic cores. The element pairs of Ag, Pd and Re, Os have been used to date core formation and core evolution events in our solar system. My experimental determination of the partitioning behavior of these important elements can be used to better understand their distribution in iron meteorites, our only samples of planetary cores. Simple fractional crystallization of a metallic core cannot explain the elemental trends observed within iron meteorite groups. I have developed a crystallization model which suggests slight inhomogeneities and mixing in the molten core were important during core evolution. As a metallic core crystallizes, liquid immiscibility may be encountered, which could significantly affect the subsequent evolution of the core. My experimental work suggests the role of liquid immiscibility during the crystallization of a metallic core is significantly smaller than the published phase diagram implies. These four topics, though each an independent project, together provide insight into the nature of the cores of terrestrial planetary bodies and the processes which affect those cores.