Diamonds in Meteorites Offer a Glimpse of the Early Solar System

These rocks formed under higher pressure than you’d normally get from an asteroid collision.

Electron microscope image of a deformed diamond matrix inside a meteorite known as Almahata Sitta MS-170.

Sometimes scientific treasure is real treasure, too.

In a new paper published in Nature Communications, Farhang Nabiei from the Swiss Federal Institute of Technology in Lausanne and colleagues analyzed a meteorite that fell in the Nubian Desert in Sudan in 2008 and found something unexpected. The rock was a ureilite, consisting mostly of the minerals olivine and pyroxene, a type previously thought to have formed either from a powerful collision between asteroids or from pressures deep within protoplanets, the building blocks from which planets formed early in our solar system’s history.

The surprise in this case was the team’s discovery of relatively large (sorry, still less than one millimeter long) diamonds inside the meteorites. Their size can only be explained if pressure within the parent body reached at least 20 gigapascals (2.9 million pounds per square inch) when it formed. That kind of pressure wouldn’t occur in asteroid collisions, but would be feasible only within a protoplanet somewhere between the size of Mercury and Mars.

Ureilites are not as rare as you might think. Hundreds of fragments have been recovered, suggesting that many protoplanets existed during our solar system’s infancy. The one that collided with Earth—sometimes called Theia was likely critical to the origin and evolution of life on our planet. Without it Earth would not have its giant—by planetary standards—moon, which kept water in the oceans as well as liquid magma underground in motion. Tidal flats are seen by many scientists as one possible location where life originated, and the Moon still has a strong effect on the life cycles of many species today. Because tidal forces exerted by the Moon help to keep our planet’s interior liquid, they’re also important for maintaining the magnetic field that shields us from cosmic radiation, and for plate tectonics, the natural recycling mechanism of the crust.

Elsewhere in the solar system, it was probably a protoplanet collision that caused Venus to rotate clockwise, while the other nearby terrestrial bodies—Mercury, Earth, and the Moon—all rotate anti-clockwise.

Nobody knows how many protoplanets were around in the early solar system, but it’s fair to speculate that many of them, including the one that collided with the early Earth, have left the solar system and are now rogue or wandering planets traveling alone through interstellar space. The study by Nabiei et al. gives us a glimpse of a time before Earth became what it is now—a home for life.

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