Mercury has a 10-mile-thick diamond mantle beneath its crust, NASA’s MESSENGER spacecraft finds.
Scientists have long been puzzled by Mercury, the smallest planet in our solar system and closest to the sun. It has several unique features that don’t match those of other planets. These include its very dark surface, dense core, and early end to volcanic activity.
One mystery is the presence of graphite patches on Mercury’s surface. This has led scientists to suggest that Mercury once had a carbon-rich magma ocean that floated to the surface, creating these patches and Mercury’s dark color.
The same process could have formed a carbon-rich mantle beneath the surface. Researchers believe this mantle isn’t made of graphene, as previously thought, but rather diamond.
A team led by Olivier Namur, an associate professor at KU Leuven, used geophysical data collected by NASA’s MESSENGER spacecraft to calculate that Mercury’s mantle is 10 miles thick and composed of diamond. They applied incredible pressure to a synthetic silicate acting as a proxy for the material found in Mercury’s mantle, replicating conditions within the planet’s interior.
The team also used computer modeling to study how minerals like those found in Mercury’s mantle changed under these conditions. They believe that two processes contributed to the formation of this diamond mantle: crystallization of the magma ocean and crystallization of Mercury’s metal core.
When Mercury formed around 4.5 billion years ago, its core was fully liquid and progressively crystallized over time. The team believes that a solubility threshold was reached, causing carbon enrichment in the residual melt, resulting in the formation of diamond.
This discovery highlights differences between Mercury’s birth and those of other rocky planets like Venus, Earth, and Mars. Mercury’s proximity to the sun likely formed its carbon-rich cloud.
Source: https://www.space.com/mercury-diamond-layer-10-miles-thick-nasa-messenger