Recent research led by scientists from the University of Liège and KU Leuven has uncovered new details about how Mercury formed, particularly focusing on the development of its core, mantle, and crust. Using experimental petrology, a scientific method that studies the composition and formation of rocks under various conditions, the researchers reconstructed the early history of Mercury. Their findings were published in several scientific journals, including Earth and Planetary Science Letters, Nature Communications, and Advances in Geochemistry and Cosmochemistry. A key part of the study examined how carbon behaved during the formation of Mercury's core and mantle. The researchers found that the oxidation state of the environment—measured by a factor called oxygen fugacity (fO2)—played a major role. In more oxidizing conditions, carbon tends to be siderophile, meaning it is attracted to the metallic core. However, Mercury's environment was highly reducing, meaning it had very little oxygen. In such conditions, carbon is less likely to go into the core and instead remains in the silicate mantle, where it eventually crystallizes into graphite. The study suggests that this graphite formed a primitive crust on Mercury, floating on top of a magma ocean. This crust would have been several tens of meters thick and is consistent with the carbon-rich layer observed on Mercury's surface today. However, this early crust was likely broken up and mixed by later meteorite impacts and volcanic activity, which shaped the planet's more recent surface. Mercury's core is unusually large, making up about 70% of the planet’s mass. To explain its lower-than-expected density, scientists have proposed that the core contains light elements like carbon, silicon, or sulfur. However, the new research shows that carbon is only present in very small amounts—less than 0.5% by mass—in the core. Instead, silicon and sulfur are the main light elements contributing to the core's lower density. These elements also help lower the melting point of iron, allowing Mercury's core to remain partially liquid for billions of years, which is essential for generating the planet's magnetic field. This research provides a new framework for understanding not only Mercury but also other planetary bodies that formed under similar reduced conditions. It could apply to early Earth, which may have formed from reduced materials, as well as hypothetical "super-Mercuries" or carbon-rich exoplanets. Future missions, such as the European Space Agency's BepiColombo, may help confirm the presence of graphite on Mercury’s surface and provide more detailed data about its composition.