NASA spacecraft finds a layer of diamonds 10-miles thick on planet Mercury

Planet Mercury is scorched and easy to overlook, yet the innermost planet keeps tossing cosmic curveballs. Now researchers suggest an even wilder twist: a layer of diamond roughly 10 miles thick may sit inside the planet.

For a world that spins three times on its axis for every two laps around the Sun and endures noon temperatures above 800 °F, that is a dazzling possibility.

Hints of carbon riches have been piling up since NASA’s MESSENGER spacecraft mapped Mercury in detail. Graphite patches spattered across the crust – graphite, an “allotrope” of carbon – point to a bygone magma ocean loaded with carbon.

When that ocean cooled, light carbon floated upward, darkening the ground, while denser metal sank inward.

Heavier carbon, the new study argues, descended alongside the sinking metal and re‑crystallized into diamond, adding a fresh twist to the planet’s story.

Recreating Mercury diamonds in the lab

The work comes from a joint team in China and Belgium led by planetary materials specialist Dr. Yanhao Lin of the Center for High Pressure Science and Technology Advanced Research (HPSTAR).

MESSENGER’s chemical readings showed more carbon than any other rocky world, so Lin’s group recreated Mercury’s interior in a lab press, squeezing synthetic mantle rock to 7 GPa, roughly seven times the pressure at the bottom of the Mariana Trench, then heating it to nearly 3,600 °F.

“Many years ago, I noticed that Mercury’s extremely high carbon content might have significant implications. It made me realize that something special probably happened within its interior.”

Mercury’s core–mantle boundary

Under those conditions, graphite is not the only option. The experiments indicate that at the core-mantle boundary – about 5.575 GPa and enriched by roughly 11 percent sulfur – carbon flips into its harder sibling, building a sparkling shell up to 18 kilometers (11 miles) thick around the metallic core.

Cooling calculations show a 358 K drop in the magma ocean once diamond begins to appear, helping the crystals sink and pile up.

“We use the large‑volume press to mimic the high‑temperature and high‑pressure conditions of Mercury’s core‑mantle boundary and combine it with the geophysical models and thermodynamic calculations,” Lin explained.

“Sulfur lowers the liquidus of Mercury’s magma ocean. If the diamond forms in the magma ocean, it can sink to the bottom and be deposited at the CMB.”

On the other hand, sulfur also helps the formation of an iron sulfide layer at the CMB, which is related to carbon content during planetary differentiation.

Sturdy magnetic field

Mercury’s magnetic field is surprisingly sturdy for a world only slightly wider than the continental United States. Heat must flow out of the core to keep the dynamo churning, and diamond is an ace conductor that funnels energy upward faster than the surrounding rock.

“Carbon from the molten core becomes oversaturated as it cools, forming diamond and floating to the CMB,” Lin continued.

“Diamond’s high thermal conductivity helps transfer heat effectively from the core to the mantle, causing temperature stratification and convection change in Mercury’s liquid outer core, and thus affecting the generation of its magnetic field.”

How Mercury got so much diamond

Mercury’s graphite veneer – described as a “primordial crust” in MESSENGER papers – already set the planet apart. If diamond truly lurks below, it widens the chemical gulf between Mercury and other rocky worlds.

Earth, Mars, and Venus lost most of their carbon to space or locked it in carbonates; Mercury appears to have hoarded it, first as floating graphite, then as sinking diamond.

“It also could be relevant to the understanding of other terrestrial planets, especially those with similar sizes and compositions. The processes that led to the formation of a diamond layer on Mercury might also have occurred on other planets, potentially leaving similar signatures,” Lin concluded.

What happens next?

The discovery leans heavily on laboratory insight because no probe has yet peered inside Mercury. BepiColombo, a joint European–Japanese mission cruising toward the planet, will slip into orbit in 2030.

Its instruments will refine gravity maps and look for twists in the magnetic field that betray a thin, superconductive layer.

A modestly thick diamond shell may leave a clear fingerprint that confirms or refutes the laboratory predictions.

Future researchers may also revisit carbon‑rich metallic asteroids.

If Mercury managed to forge diamond under modest pressure, smaller bodies could follow suit, spicing up asteroid‑mining dreams – even if any gems are locked beneath iron skins, not loose pebbles ripe for harvest.

Why does any of this matter?

The tale is not about jewelry; it is a lesson in planetary evolution. Carbon’s behavior – floating, sinking, switching structure – shapes heat flow, crust makeup, and even the shielding field that deflects solar wind.

By tracing carbon’s journey on Mercury, scientists sharpen models that apply to worlds circling distant stars. A planet baked dry and loaded with carbon might look lifeless at first glance, yet deep interiors could dance with diamond phases that keep cores alive.

Mercury, often written off as a scorched ball of rock, shows that worlds can host exotic physics, hiding secrets worth chasing.

The full study was published in the journal Nature Communications.

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