How Mercury formed its graphite crust and core

The study by researchers at the University of Liège and KU Leuven used experimental petrology to simulate the conditions under which Mercury formed its core and crust. They recreated the high-pressure, high-temperature environment of the planet's early stages, focusing on the behavior of carbon during the separation of the metallic core from the silicate magma. The experiments revealed that carbon's preference for metal depends on the oxidation state of the environment. Under oxidizing conditions, carbon is strongly siderophile and enters the core, but under reducing conditions, it becomes less siderophile and remains in the silicate magma, crystallizing as graphite.

The research determined that Mercury's graphite crust is about 40–120 meters thick, consistent with the carbon-rich layer observed on its surface. The study also found that the core remains low in carbon, less than 0.5%, which explains the planet's density deficit. This suggests that the core is primarily composed of silicon and, to a lesser extent, sulfur, which lowers the melting point of iron, allowing the core to remain liquid for 4.5 billion years. The findings provide insights into the formation of other highly reduced bodies, including exoplanets and early Earth.

The research was published in several scientific journals, and the findings are expected to be confirmed by future missions like BepiColombo. The study highlights the importance of understanding Mercury's early evolution and the role of carbon in its crust and core formation.

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