Nearly Carbon-Saturated Magma Oceans in Planetary Embryos During Core Formation

A planetary mantle after core formation has been thought to be highly depleted in carbon due to its strong siderophile behavior. However, the carbon contents in lunar and terrestrial mantles are much greater than experimental predictions; thus, how the carbon contents in terrestrial mantles were established is puzzling and poorly understood. Here, we present high-pressure experiments on the metal-silicate partitioning of carbon at 2 GPa and 1923 K in a system containing 0.2 wt% C, which is close to that in enstatite chondrites, and show that a magma ocean made of chondritic materials is nearly saturated with carbon even under metal saturation. The consistency between the solubility of carbon in silicate melts and the carbon contents in lunar and terrestrial mantles also supports a nearly carbon-saturated magma ocean during core formation and suggests that carbon contents in terrestrial mantles may have been established during the main accretion phase.