New research suggests that Mercury, the smallest planet in the solar system and closest to the Sun, may harbor a layer of diamonds up to 18 kilometers (11 miles) thick beneath its surface. These diamonds could have formed around 4.5 billion years ago during Mercury's early development from a cloud of dust and gas. At that time, Mercury is believed to have had a graphite crust floating over a deep magma ocean, creating a high-pressure, high-temperature environment conducive to diamond formation.

To test this theory, a team of researchers used an anvil press, a machine typically employed for studying materials under extreme conditions or producing synthetic diamonds. The team, led by Bernard Charlier from the University of Liège in Belgium, simulated Mercury's early interior by placing a synthetic mixture of elements like silicon, titanium, magnesium, and aluminum inside a graphite capsule. This capsule was subjected to pressures 70,000 times greater than those on Earth's surface and temperatures up to 2,000 degrees Celsius (3,630 degrees Fahrenheit). Under these conditions, the graphite transformed into diamond crystals.

This research offers new insights into Mercury's hidden interior and could also provide clues about the internal structure and evolution of exoplanets with similar characteristics. Mercury, the second densest planet after Earth, has a large metallic core that makes up 85% of its radius. Despite its significance, Mercury remains one of the least explored terrestrial planets.