Mercury, the planet closest to the sun, has a 10-mile-thick mantle of pure diamond, according to NASA.

The report, derived from data taken from the NASA MESSENGER probe that orbited the red-hot planet for four years and plunged into its surface in 2015, suggests a 10-mile-thick layer underneath the planet’s crust previously thought to consist of graphite is actually diamond, according to Space.com.

The study reports Mercury initially went through a stage in which its surface consisted of a “magma ocean.” This, combined with Mercury’s proximity to the sun, would cause its contents to be subjected to considerable pressure and heat over a long period of time. Under such conditions, carbon can turn into graphite. On a planet with a high concentration of sulfur, such as Mercury, carbon subjected to such conditions would slowly transform into stable diamond, according to the report.

One of the co-authors of the study, Yanhao Lin from the Center for High Pressure Science and Technology Advanced Research in Beijing, said reflective surfaces on Mercury that suggested the presence of carbon led to the discovery.

“Many years ago, I noticed that Mercury’s extremely high carbon content might have significant implications. It made me realize that something special probably happened within its interior,” Lin said.

The report further suggests a mantle of diamond above a liquid core would create a magnetic field. The presence of a magnetic field on Mercury has puzzled scientists for years.

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For prospective Mercurian diamond miners, the extraction of the valuable commodity would be a difficult task, since the mantle begins 300 miles below the planet’s surface, and considering Mercury is an intolerably hostile environment in the first place. The surface temperature can range from 800 degrees to minus 290, and the planet has almost no atmosphere.

The next mission to survey Mercury, named BepiColombo, is being run by the European Space Agency and will begin surveying the planet in 2026. The mission was launched in 2018.