Mercury may have a 10-mile-thick layer of diamonds

A thick diamond layer inside Mercury

Scientists using data from NASA’s MESSENGER spacecraft have said Mercury may have a 10-mile-thick (16-km-thick) diamond layer beneath its crust. The scientists believe a subterranean magma ocean and the planet’s metal core crystallized under intense pressure. They said the ocean and core would have been saturated in carbon. And with the help of high pressure-temperature experiments, thermodynamic models and the most recent geophysical models of the internal structure of the planet, they determined Mercury was capable of producing a thick diamond layer.

The team of scientists from China and Belgium published their peer-reviewed study in the journal Nature Communications on June 14, 2024.

Diamonds form from carbon under high pressure

Mercury is the closest planet to the sun in our solar system. Scientists have long believed the little planet has large, dark patches of graphite on its surface. Graphite is a crystallized form of carbon made of stacked layers of graphene. This graphite suggested Mercury might once have had a subterranean magma ocean, and magma that reached the planet’s surface would have created the solidified graphite pools. But instead of a graphite mantle under the crust, scientists said part of it might be diamond.

The rocky planets tend to have three main layers: a core, mantle and crust. The scientists said that – due to the amount of pressure in the planet’s interior – the boundary between the core and mantle should have turned to diamond. The magma ocean mantle would have crystallized at the boundary with the core. Not only that, but some of the core itself – which would have been liquid in the planet’s early days – would have crystallized over time, too, forming diamonds. Diamond is less dense than metal, so it would have floated to the top of the planet’s core.

These diamonds – if they exist – would lie hundreds of miles/kilometers below the planet’s crust. So they would not be a feasible target for a mining mission.

Diamonds in other locations in the solar system

Because Mercury is so close to the sun, it was exposed to more carbon in the cloud of gas and dust that formed the sun. So Mercury contains more carbon than the other inner planets (Venus, Earth and Mars). But scientists have suggested that Earth, also, has a diamond layer at the boundary of the core and mantle. So diamonds are not rare in our solar system.

In fact, scientists have thought for decades that diamonds may be found in the cores of Uranus and Neptune. And Jupiter and Saturn may be awash in diamonds, with their deep atmospheres containing chunks of diamond floating in a liquid hydrogen/helium fluid. Meteorites have diamonds, too. In 2022, scientists reported finding diamonds in four meteorites picked up in North Africa.

Bottom line: An international team of scientists have said Mercury may have a layer of diamonds 10 miles (16 km) thick near the boundary of the planet’s core and mantle.

Source: A diamond-bearing core-mantle boundary on Mercury

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