Diamond-Encrusted Meteorite Could Be From a Lost Planet
Something fell from the sky in the Nubian Desert of Sudan in 2008, and it could be a key to understanding lost planets from the early formation of our solar system.
In research published today in Nature Communications, a group of planetary scientists provide evidence that a fragment of a meteorite may be a piece of a protoplanet that was destroyed as the solar system was forming. This early formation period was a chaotic and violent time, and the four inner solar system planets are the only survivors of a brutal series of collisions. Several protoplanets amassed together, striking each other, fragmenting, coalescing, and repeating the process to finally form the rocky planets, moons and asteroids we see today.
The meteorite is thought to be a fragment from a large protoplanet, between the sizes of Mercury and Mars. Previously, scientists thought protoplanets did not get much larger than dwarf planet Ceres, or about a sixth the diameter of Mercury. The space rock in question is a unique type of stony meteorite called a ureilite, owing to the area of Russia where they were first found, Urey. Ureilites have been previously discovered, but the reported rock is the first evidence that they may have originated in large protoplanets.
“Either we know [other meteorites] aren’t coming from a large planet, or we don’t know exactly what kind of planet it was,” Farhang Nabiei of the École Polytechnique Fédérale de Lausanne who co-authored the study says. “This is the first time we know a sample came from such a large body.”
The meteorite likely formed at pressures around 20 gigapascals, which on Mars corresponds to the core-mantle boundary. This suggests the rock formed deep within an object the size of a current inner solar system planet. The proof is in the diamonds that formed in the rock, which have been polluted with elements and compounds that generally form under these intense pressures. Graphite samples from the rock also show evidence that they were likely once diamonds that, in the impacts, melted and re-congealed into graphite.
The meteorite also contains iron-sulfur compounds but lacks silicates, which are typically found higher up in planets. Some of those iron-sulfur compounds have leached into the nanodiamonds. The diamonds themselves may have been larger until the protoplanet was destroyed.
Ureilites all likely came from this parent body, albeit at different depths throughout. “There is much evidence that they’re related,” Nabiei says. But there’s no line of evidence suggesting that it came from the giant protoplanet that collided with Earth to form the moon.
If this is where the meteorite formed, it confirms that some early solar system protoplanets were quite large. The protoplanet in question may have originated in the outer solar system and migrated inward to the inner solar system. The study also demonstrates that wherever the protoplanet once was, it has long since been destroyed, leaving behind only a series of ureilites, some of which come crashing down for scientists on Earth to study.
The rock is a fossil from a lost world—and it could be a clue to unlocking the secrets of the turbulent early solar system.