Precious Mercury: 18 km of diamonds in the lead role

Mercury is the smallest planet in the Solar System, orbiting closest to its star, second only to Earth in density. It formed about 4.5 billion years ago from a swirling cloud of dust and gases under crushing pressure and hellishly high temperatures.

Astronomers believe Mercury’s crust is a thick layer of graphite floating on an ocean of magma. Mercury’s surface is less than 15 percent of Earth’s, and its metallic core is as much as 85 percent of Earth’s diameter, so its mantle and crust are relatively thin.

18 kilometers of diamonds

Mercury still holds many secrets. One of them may be a real treasure. Scientists from Belgium have recreated the conditions that probably existed during the formation of the graphite crust and the magmatic ocean below. It turned out that these are excellent conditions for the formation of other crystal structures from carbon.

Scientists have prepared a miniature version of Mercury. A mixture silicon, titanium, magnesium, aluminum and other elements that are part of Mercury’s composition, were enclosed in a graphite capsule. An important role was also played by sulfur, present in large quantities on the planet, allowing carbon crystals to form at a lower temperature (diamonds formed in the presence of sulfur are more stable). The model then landed in a monstrous press used, among other things, to test materials and produce synthetic diamonds.

The sample was melted at a temperature of 2,000 degrees and pressure 70,000 times greater than that which occurs naturally on Earth. After the experiment, the material was put under an electron microscope. Scientists found diamond structures in it.

What does this mean for full-size Mercury? There are definitely diamonds beneath the planet’s surface. The layer with unique crystals may be between 15 and 18 kilometers thick. And these are not the unattractive “industrial diamonds” that we find on files, but large crystals, suitable for cosmically expensive jewelry. However, we probably won’t dig them up – They are located at a depth of a good 500 kilometers. Our only hope is that geological processes brought some of the treasure to the surface… and that we find an exoplanet with similar processes, but at a shallower depth.

Mercury’s diamond formation is still ongoing as the planet’s core cools. The magmatic ocean is probably colder and deeper than originally thought. Unfortunately, we don’t have samples from Mercury yet, but it is certain that its chemistry is different from that of Earth, the Moon, or Mars. This is due to its proximity to the Sun, and consequently, its low oxygen levels.

We will learn more in December 2025, when the BepiColombo mission probes enter Mercury’s orbit.