Physical and chemical properties of Earth and planetary materials (particularly melts) under ultra-high pressures
Ohtani was the first person to conduct melting experiments on mantle minerals and rocks to the mantle transition zone using the multi-anvil high pressure apparatus. He determined the melting relations of mantle minerals up to the pressures equivalent to those of the uppermost lower mantle. He also developed techniques to measure the density of molten rocks under very high pressures and constrained density contrasts between melts and minerals. This pioneering work led to the development of the deep magma ocean model in 1985. Since the mid-1990s, Ohtani has made studies on water storage in the mantle. He measured the solubility of hydrogen in nominally anhydrous minerals such as wadsleyite, ringwoodite, and bridgmanite and demonstrated that the presence of water in mantle minerals significantly affects their phase boundaries, which can explain the topographic variations in the 410 km and 660 km seismic discontinuities. Professor Ohtani actively explored the mantle-core boundary and the Earth’s core and made impactful contributions on element partitioning between the mantle and core and on phase relations in the iron-light elements systems, and demonstrated that both O and Si are the most likely light-element constituents in the outer core. In addition, he investigated high pressure polymorphism in shocked meteorites, and discovered coesite, stishovite, and seifertite (one of the post-stishovite SiO2 polymorphs) in lunar materials, and the olivine breakdown to periclase plus bridgmanite in a shocked Martian meteorite.