The Earth and other terrestrial planets were differentiated through metal-silicate separation, forming iron-nickel metallic cores with dissolved light elements such as sulfur, oxygen, silicon, carbon, and hydrogen. Subsequent cooling led to the crystallization of the inner core of some planets. One of my major research goals is to identify the light elements in the cores using an integrated approach, including element partitioning experiments, liquid metal percolation in molten or crystalline silicate matrix, and simultaneous measurements of density and sound velocities at high pressure and temperature. The ultimate goal is to establish comprehensive geochemical models of the planetary cores which are also consistent with the geophysical observations.

Several new developments and collaborations in recent years have opened up research opportunities at the interface of petrology, mineral physics, geochemistry, and geophysics. These include the combined capability of dynamic and static experiments to produce an integrated dataset on density and velocity of solid and liquid core alloys over a wide P-T range that is essential for modeling the densities and velocities of the Earth’s liquid outer core and solid inner core. Our shock wave experiments in the Fe-S, Fe-Si, and Fe-S-O systems, which yielded both densities and sound velocities of Fe alloys under liquid outer core conditions, have demonstrated that the simultaneous fit to both density and sound velocity is a powerful way to decipher the identity of the lighter alloying elements in the core. These shock compression measurements can be further strengthened by accurate P-V-T measurements of the same alloys in diamond-anvil cells and the longitudinal sound velocity measurements of solid iron alloys at high temperature by the inelastic x-ray scattering (IXS) technique. I have launched a new project to integrate results from dynamic and static compression experiments on the same samples, which allows us to obtain complimentary data over a wide P-T range and establish a self-consistent database from two independent high-pressure experiments. The expected results should lead to significant advances in our understanding of the composition of the core.