Mercury could have an 11-mile underground layer of diamonds, researchers say

(CNN) — A layer of diamonds up to 18 kilometers (11 miles) thick could be tucked below the surface of Mercury, the solar system’s smallest planet and the closest to the sun, according to new research.

The diamonds might have formed soon after Mercury itself coalesced into a planet about 4.5 billion years ago from a swirling cloud of dust and gas, in the crucible of a high-pressure, high-temperature environment. At this time, the fledgling planet is believed to have had a crust of graphite, floating over a deep magma ocean.

A team of researchers recreated that searing environment in an experiment, with a machine called an anvil press that’s normally used to study how materials behave under extreme pressure but also for the production of synthetic diamonds.

“It’s a huge press, which enables us to subject tiny samples at the same high pressure and high temperature that we would expect deep inside the mantle of Mercury, at the boundary between the mantle and the core,” said Bernard Charlier, head of the department of geology at the University of Liège in Belgium and a coauthor of a study reporting the findings.

The team inserted a synthetic mixture of elements — including silicon, titanium, magnesium and aluminum — inside a graphite capsule, mimicking the theorized composition o...