MERCURY might be hiding a miles-thick hoard of solid diamonds beneath its surface.
Our solar system’s innermost planet has puzzled scientists for decades.
It has a weak magnetic field, just 1% the strength of Earth’s. It has a massive core in relation to its puny size. And despite being the smallest planet in the solar system, it is the second densest.
These features have made it a topic of fascination for years – and now, it seems researchers have uncovered yet another curious detail.
A study published June 14 in Nature Communications suggests Mercury’s core-mantle boundary includes a diamond layer.
The diamond layer is between 9 and 11 miles thick and nestled deep within the planet’s interior.
Nasa’s MESSENGER spacecraft, the first to visit Mercury in thirty years, mapped the entire planet and revealed its surface is rich with carbon.
Researchers proposed they were looking at the remnants of an ancient layer of graphite that was pushed to the surface.
This theory suggests Mercury once had a molten surface layer or magma ocean containing a large amount of carbon. As the planet cooled, this carbon formed a graphite crust.
But scientists now believe there’s more to the picture – and this is where the mantle, or middle layer, comes in.
Researchers long suspected the mantle’s temperature and pressure were the right conditions for carbon to form graphite.
As it was lighter than the mantle, the graphite then floated to the surface.
But more recent evidence indicated that Mercury’s mantle may be 80 miles, or 50 kilometers, deeper than previously thought.
This means pressure and temperature at the boundary between the core and the mantle are significantly higher – and these extreme conditions could prompt carbon to crystallize, forming diamonds.
To study Mercury’s interior, researchers used a combination of high-pressure and temperature experiments and thermodynamic modeling.
They managed to achieve pressure levels seven times those found at the deepest parts of the Mariana Trench.
Under these conditions, the scientists examined how minerals in the planet’s interior melt and reach equilibrium phases.
The diamond layer is believed to be between between 15 and 18 kilometers, or 9 and 11 miles, thick.
But it’s inaccessible for now. The minerals are buried around 300 miles, or 485 kilometers, below the surface – and space explorers would first have to brave the planet’s extreme heat.
The paper proposes that the crystallization of the core led to the formation of a diamond layer at the core-mantle boundary.
They also suggest that the present temperature at the boundary is close to the point where graphite can turn to diamond, stabilizing the temperature as a result.
The experiments demonstrated that minerals like olivine likely formed in the mantle, in line with previous studies.
The team took the experiment a step further by adding sulfur, another mineral that is commonplace on the planet’s surface.
This adjustment produced a 358 Kelvin temperature change in Mercury’s magma ocean.
Under these conditions, diamonds may have crystallized when Mercury’s inner core solidified, the team deduced.
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Co-author Yanhao Lin said the results have implications for understanding the formation of carbon-rich exoplanets.
“It also could be relevant to the understanding of other terrestrial planets, especially those with similar sizes and compositions,” Lin explained.
“The processes that led to the formation of a diamond layer on Mercury might also have occurred on other planets, potentially leaving similar signatures.”
