Oxygen Driving Hydrogen Into the Inner Core: Implications for the Earth's Core Composition

Abstract Earth's core should contain light elements to account for the density deficit relative to pure iron as inferred from seismic observations. Of particular interest is hydrogen, as planetary accretion models predict the delivery of water possibly sequestered in the core. In this study, we investigate the partitioning of hydrogen across the inner‐core boundary using extensive atomistic simulations with machine learning potentials. While showing the tendency of hydrogen to dominantly remain in the liquid phase during inner core solidification, we find that the presence of oxygen would drive more hydrogen into the inner core, where 7 mol% oxygen even reverses the partitioning of hydrogen. By considering such mutual influences of partitioning among light elements in the core, we propose that the inner core can be an important reservoir of primordial hydrogen along with its growth.