Mercury, the smallest planet in our solar system, continues to fascinate scientists with its unique characteristics and enigmatic features. Recent research suggests that Mercury may harbour a layer of diamonds hundreds of miles below its surface. These findings, published in the journal Nature Communications, could provide crucial insights into the planet’s composition and its unexpected magnetic field.
THE DIAMOND HYPOTHESIS
The hypothesis of a diamond layer on Mercury stems from the planet’s high carbon content. According to the study, Mercury likely formed similarly to other terrestrial planets, starting with a hot magma ocean rich in carbon and silicate. As the planet cooled, metals coagulated to form a central core, while the remaining magma crystallized into the mantle and outer crust.
For years, it was believed that the mantle’s temperature and pressure were sufficient to form graphite, which then floated to the surface. However, a 2019 study suggested that Mercury’s mantle might be deeper than previously thought, significantly increasing the pressure and temperature at the core-mantle boundary. These conditions could allow carbon to crystallize into diamond instead of graphite.
SIMULATION EXPERIMENTS
To explore this possibility, scientists from Belgium and China, including co-author Yanhao Lin from the Center for High Pressure Science and Technology Advanced Research in Beijing, conducted experiments and simulations. They created chemical mixtures resembling Mercury’s early magma ocean, including iron, silica, carbon, and varying amounts of iron sulphide. These mixtures were subjected to extreme pressures and temperatures using a multiple-anvil press, simulating conditions deep within Mercury.
Computer models were also used to refine measurements of the pressure and temperature at the core-mantle boundary and to simulate the stability of graphite and diamond under these conditions. The experiments indicated that the presence of sulphur in the chemical mixtures led to solidification at much higher temperatures, favouring diamond formation.
RESULTS AND IMPLICATIONS
The study’s findings suggest that diamonds could have crystallized during Mercury’s early formation, forming a layer with an average thickness of about 14.5 kilometres (9 miles). These diamonds, less dense than the core, would have floated up to the core-mantle boundary.
While mining these diamonds is not feasible due to their depth (about 300 miles or 485 kilometres below the surface) and Mercury’s extreme temperatures, the presence of a diamond layer may have significant implications. The diamonds could facilitate heat transfer between the core and mantle, potentially influencing Mercury’s magnetic field by causing liquid iron to swirl and create magnetism.
BROADER IMPACTS
Insights into Exoplanets
The processes leading to diamond formation on Mercury might also occur on other carbon-rich exoplanets, potentially leaving similar signatures. Understanding these processes could enhance our knowledge of planetary formation and evolution beyond our solar system.
Future Missions
More clues about Mercury’s composition and magnetic field may come from BepiColombo, a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency. Launched in 2018, BepiColombo is expected to begin orbiting Mercury in 2025, providing further data to validate or refine these findings.
The discovery of a potential diamond layer on Mercury opens new avenues for understanding the planet’s unique characteristics and composition. While these diamonds remain out of reach, their existence could help solve some of the biggest mysteries about Mercury and offer insights into the formation of other planets. As future missions like BepiColombo gather more data, we may soon unlock more secrets of this enigmatic planet.