It is not a rock, there is a layer of diamond 18 km thick at the heart of Mercury

The planet Mercury has rows of diamonds in it. Reaching a thickness of up to 18 kilometers, what does it look like?

Previously, this diamond coating was discovered by researchers from China and Belgium. The research was led by Dr Yanhao Lin from the High Pressure Science and Technology Research Center (HPSTAR) in Beijing. Researchers are interested in finding out more about the particular planet and its true conditions.

Mercury has a dark, rocky surface. Its dense metallic core has been the focus of extensive research, particularly through NASA’s MESSENGER space probe, which orbited Mercury from 2011 to 2015.

This mission revealed amazing insights into the composition and history of the planet. Among the most interesting discoveries was the presence of large amounts of graphite, a type of carbon, on Mercury’s surface.

A History Rich in Carbon Mercury

Previous missions have shown that Mercury’s surface graphite comes from ancient layers that float from the molten surface layer or magma ocean. As the mercury cools, this carbon forms a crust of graphite. However, Dr Lin and his team challenged the hypothesis that graphite was the only phase containing carbon during the crystallization of Mercury’s magma ocean.

“Years ago, I noticed that Mercury’s very high carbon content could have a big effect. That made me realize that something special could be happening in its interior,” he explained on the last page of Earth announced Monday (5/8/2024).

Inside the Mercury Diamond

To investigate, the researchers recreated conditions inside Mercury using high pressure and temperature experiments combined with thermodynamic modeling.

They used synthetic silicates to mimic the composition of Mercury’s mantle, reaching pressure levels of up to 7 Giga Pascal (GPa), about seven times the pressure found in the deepest parts of the Mariana Trench.

“We used a giant press to simulate the high-temperature and high-pressure conditions at the boundary of Mercury’s core and combined them with geophysical models and thermodynamic calculations,” Lin said.

Under these extreme conditions, the team studied how minerals in Mercury’s interior melt and reach equilibrium levels, focusing on graphite and diamond.

They also analyzed the chemical composition of their experimental samples. The results were quite surprising. By combining experimental data with geophysical simulations, the researchers estimate that the pressure of Mercury’s CMB (Mercury’s Core-Mantle Boundary) is around 5,575 GPa. At a sulfur content of about 11%, they observed a significant temperature change of 358 Kelvin in Mercury’s magma ocean.

This led them to suggest that although graphite was the main phase of carbon during the crystallization of the magma ocean, the underlying crystallization may have formed layers of diamond.

“Sulfur reduces Mercury’s magma ocean fluids.” If diamonds form in the magma ocean, they can sink to the bottom and settle in the CMB. On the other hand, sulfur also helps to form layers of iron sulfide in the CMB, which is related to the carbon content during planetary differentiation,” explained Dr. Lin.

Through this research, Dr Lin shows wider implications for understanding other terrestrial planets.

“This could also be relevant for understanding other terrestrial planets, especially those that are similar in size and composition. The processes that led to the formation of diamond layers on Mercury could also occur on other planets, which could leave similar traces,” he concluded.

(nir/nwk)