Mercury may have a thick layer of diamond hundreds of miles below its surface, a new study shows. The findings, published June 14 in the journal Nature Communicationscould help solve mysteries about the planet’s composition and unique magnetic field.
mercury it is full of mysteries. For one, it has a magnetic field. Although it is much weaker than Earth’s, magnetism it is unexpected because the planet is small and appears to be geologically inactive. Mercury also has extremely dark surface spots that NASA’s Messenger mission identified as graphite, a form of carbon.
This last feature is what piqued his curiosity Yanhao Lin, a staff scientist at the Advanced Research Center of High Pressure Science and Technology in Beijing and co-author of the study. Mercury’s extremely high carbon content “made me realize that something special probably happened in its interior,” he said in a STATEMENT.
Despite Mercury’s oddities, scientists suspect that it probably formed the way other terrestrial planets did: from the cooling of a hot magma ocean. In the case of Mercury, this ocean was likely rich in carbon and silicates. First, metals solidified within it, forming a central core, while the remaining magma crystallized into the planet’s middle mantle and outer crust.
For years, researchers thought the temperature and pressure of the mantle were high enough carbon to form graphite, which, being lighter than the mantle, floated to the surface. But a 2019 STUDY suggested that Mercury’s mantle may be 80 miles (50 kilometers) deeper than previously thought. This would greatly increase the pressure and temperature at the boundary between the core and the mantle, creating conditions where carbon could crystallize into diamond.
To investigate this possibility, a team of Belgian and Chinese researchers, including Lin, collected chemical soups that included iron, silica and carbon. Such mixtures, similar in composition to certain types meteorites, thought to mimic the magma ocean of infant Mercury. The researchers also spiked these soups with varying amounts of iron sulfide; they realized that the magma ocean contained a lot of sulphur, as today’s surface of Mercury is also rich in sulphur.
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Using a multi-anvil press, the team subjected the chemical mixtures to crushing pressures of 7 gigapascals – roughly 70,000 times the pressure of the Earth’s atmosphere at sea level – and temperatures of up to 3,578 degrees Fahrenheit (1,970 degrees Celsius). These extreme conditions simulate those deep inside Mercury.
In addition, the researchers used computer models to obtain more accurate measurements of the pressure and temperature at Mercury’s core-mantle boundary, in addition to simulating the physical conditions under which graphite or diamond would be stable. Such computer models, according to Lin, tell us about the basic structures of a planet’s interior.
The experiments showed that minerals such as olivine likely formed in the mantle—a finding that was consistent with previous studies. However, the team also found that adding sulfur to the chemical liquor only caused it to solidify at much higher temperatures. Such conditions are more favorable for the formation of diamonds. Indeed, the team’s computer simulations showed that, under these revised conditions, diamonds may have crystallized when Mercury’s inner core solidified. Because it was less dense than the core, it then floated up to the core-mantle boundary. The calculations also showed that diamonds, if present, form a layer with an average thickness of about 9 miles (15 km).
However, mining these gems is not exactly feasible. In addition to the planet’s extreme temperatures, diamonds are too deep — about 300 miles (485 km) below the surface — to be mined.
But the gems are important for another reason: they may be responsible for Mercury’s magnetic field. The diamonds could help transfer heat between the core and mantle, which would create temperature changes and cause the liquid iron to spin, creating a magnetic field, Lin explained.
The results may also help explain how carbon-rich exoplanets evolve. “The processes that led to the formation of a diamond layer on Mercury may have also occurred on other planets, potentially leaving similar signatures,” Lin said.
More data may come from BepiColombo, a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency. Launched in 2018, the spacecraft is scheduled to begin orbiting Mercury in 2025.
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