Mercury is the smallest and closest planet to the sun in the solar system. Mercury’s surface is riddled with deep craters, much like Earth’s moon. Mercury experienced a violent period known as the Late Heavy Bombardment, during which the terrestrial planet and the rest of the solar system faced an intense spike in asteroid strikes four billion years ago.
A diamond treasure trove could be sown into Mercury’s cratered crust. Planetary scientist Kevin Cannon reported at the Lunar and Planetary Science Conference in The Woodlands, Texas, that billions of years of meteorite impacts may have flash-baked much of Mercury’s surface into the glittery gemstones. His computer simulations predict that such impacts may have transformed about one-third of the little planet’s crust into a diamond stockpile many times that of Earth’s.
Diamonds are forged under immense pressures and temperatures. On Earth, the gemstones crystallize deep underground — at least 150 kilometers down — then ride to the surface during volcanic eruptions. But studies of meteorites suggest diamonds can also form during impact.
“When those [impacts] happen, they create very high pressures and temperatures that can transform carbon into diamond,” says Cannon, of the Colorado School of Mines in Golden.
There’s they could produce no reason to doubt that diamonds in this manner. Later impacts would have most likely destroyed some of the gemstones.
Simone Marchi
Diamonds form 100 miles or so below the surface of the Earth’s upper mantle. Carbon atoms bond together under extreme pressure and heat. According to Science News, the gemstones then rise to the surface during volcanic eruptions. However, meteorite studies indicate that radiant gems can form as a result of asteroid impacts.
Researchers turned to Mercury to investigate the possibility of impact-born diamonds because previous surveys of the planet and molten rock revealed the presence of graphite, a carbon-rich mineral, on the surface.
With impact-born diamonds on his mind, Cannon turned to the nearest planet to the sun. Surveys of the planet’s surface and experiments with molten rock indicate that the planet’s crust may contain fragments of an old shell of graphite, a mineral made of carbon. “What we think happened is that when [Mercury] first formed, it had a magma ocean, and graphite crystallized out of that magma,” Cannon explains.
Then came the bombardment. Mercury’s surface is heavily cratered today, indicating an impact-rich past. Cannon hypothesized that much of the purported graphite crust would have been battered and transformed into diamond.
Cannon used computers to simulate 4.5 billion years of impacts on a graphite crust to see how widespread this diamond forging could have been. The findings show that if Mercury had a 300-meter-thick graphite skin, the battering would have produced 16 quadrillion tons of diamonds — roughly 16 times Earth’s estimated reserves.
“There’s no reason to doubt that diamonds could be produced in this manner,” says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who was not involved in the study. But how many might have survived, he says, is another story. Later impacts would have most likely destroyed some of the gemstones.
Cannon agrees that subsequent impacts would most likely destroy some diamonds. However, because the ultimate melting point of diamond exceeds 4000° Celsius, the losses would have been “very limited,” he claims. Future simulations, he says, will include remelting from impacts to refine the potential size of Mercury’s current diamond reserves.
When the BepiColombo mission arrives on Mercury in 2025, it may be possible to scout for diamonds. According to Cannon, diamonds have a distinct signature of infrared light. “This could potentially be detected.”
Using computer simulations, scientists modeled the effects of frequent impacts on the first 12 miles of the planet’s crust over billions of years. According to Wired, the team discovered that the graphite could have been more than 300 feet thick and that the impact of a meteorite was powerful enough to convert 30 to 60% of the carbonaceous mineral into diamonds. Under those conditions, it is estimated that 16 quadrillion space gems will riddle Mercury, but they are most likely tiny, scattered, and buried underground.
