A piece of missing planet found in the Sahara Desert

Earth once had a sibling. And a piece of it was found in the Sahara Desert.

4.5 billion years ago, a massive world orbited our sun before likely crashing into another celestial body and shattering into rubble.

Its fragments were scattered across the young solar system — and at least one of them landed on Earth.

This secret piece of our solar system's history is known as the Northwest Africa (NWA) 12774 angrite meteorite.

Angrites are some of the oldest known volcanic rocks in the solar system. They’re incredibly rare: of the more than 80,000 meteorites discovered on Earth, only 68 are angrites.

“The materials that formed the angrite parent body are fundamentally different from the ingredients of Earth and Mars. It points to a distinct and separate evolutionary path in planetary formation in the early history of our solar system,” says Aaron Bell, an assistant research professor in the Department of Earth Science at the University of Colorado Boulder.

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While Bell and his colleagues studied the meteorite, they found it contained clinopyroxene. It’s exceptionally rich in aluminum, and a clear sign that the rock formed under enormous pressure deep underground. 

The researchers then reconstructed conditions that might have been present for the meteorite to form. 

It needed at least 17.5 kilobars of pressure. For comparison, the deepest point on Earth, the Mariana Trench, is only around 1 kilobar.

But the crystals inside the meteorite still preserved sharp edges and delicate chemical patterns. If they formed deep underground, that would have been erased. For this to happen, the crystals would likely have formed at relatively shallow depths — indicating the world had to be even larger.

This means the angrite parent body might have been comparable in size to Earth’s moon and maybe even approaching the size of Mars.

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“It’s incredible to think there was once a world this large,” Bell said. “We only know it existed because a few fragments of it happened to land on Earth. These meteorites preserved evidence of a completely different pathway through which early planets developed.”

This culminates in the first evidence of the existence of this lost planetary embryo, or protoplanet. And long-held assumptions about how planets evolve are now being challenged by its unique geological makeup.

“There are many meteorites sitting in drawers that haven’t been thoroughly studied, so there were likely more of these protoplanets we don’t know about,” Bell said. 

Content writer Ada Wood enjoys exploring the stories that science and climate teach us about our natural world and how it influences the way we live in it.