Somewhere in the Sahara, a dark stone waited for years before a collector and then a laboratory brought its story to light. Its catalog name, NWA 12774, marks it as one of the rare angrites, a group so scarce and so ancient that it preserves the earliest chapters of the solar system's making. Now a new study reads its crystals as a message from a world that no longer exists: a body perhaps as large as the Moon or Mars, shattered in a collision long before Earth had settled into its present form. It is a reminder that the planets we see today were not the only attempts at building worlds, and t
Rare Sahara Meteorite May Be Fragment of a Lost Early Solar System Protoplanet
A world we know only because a few fragments happened to land on Earth
Mark
So what's actually new here? Angrites have been known for a while.
Mimi
The origin story is new. They were assumed to come from small asteroids because of their low silica. This study argues one of them, NWA 12774, formed under pressures a small asteroid couldn't produce.
Mark
What's the evidence for that pressure?
Mimi
Clinopyroxene rich in aluminum. That chemistry points to extremely high pressure, possibly a high-energy collision.
Luke
I'd flag that the size is an inference, not a measurement. Nobody has seen this body. The radius of at least 621 miles and up to 1,118 miles comes from the researchers' reasoning about the pressure and the sharp edges.
Mark
And the headline says protoplanet, while the study says may have been?
Luke
Right. The phrasing is hedged for good reason. "If it existed" is in the reporting itself, and it's one meteorite's chemistry.
Mimi
Still, the scale comparison is striking. Up to 1,118 miles in radius sits near the moon's 1,080 miles, though well short of Mars at 2,106.
Mark
Why does it matter for Earth?
Mimi
The researchers speculate that fragments of this body may have helped build other terrestrial planets, Earth included.
Luke
Speculate is the key word. What happened to the protoplanet is unclear, and nothing in the reporting confirms that Earth contains any of it.
Mark
So what would firm it up?
Luke
The reporting doesn't say, but more angrites showing the same signature would be the obvious place to look.
Il Polso
- A single stone from the Sahara, found in 2019, carries a chemical signature that scientists say should be impossible for a small asteroid to produce.
- Its high-pressure mineral traces point to a violent, high-energy collision that once destroyed a body possibly larger than the Moon.
- Researchers are working to test whether this one meteorite is a lone anomaly or the first clue to a whole lost family of early worlds.
- The team's interpretation is still resting on one rock, so the next step is checking whether other angrites carry the same evidence of a vanished protoplanet.
Somewhere in the Sahara, a dark stone waited for years before a collector and then a laboratory brought its story to light. Its catalog name, NWA 12774, marks it as one of the rare angrites, a group so scarce and so ancient that it preserves the earliest chapters of the solar system's making. Now a new study reads its crystals as a message from a world that no longer exists: a body perhaps as large as the Moon or Mars, shattered in a collision long before Earth had settled into its present form. It is a reminder that the planets we see today were not the only attempts at building worlds, and that some of those attempts were lost, their remains scattered across space and occasionally across our own deserts.
In 2019, a rock was pulled from the Sahara Desert and given the catalog name NWA 12774. Under polarized light, a thin slice of it reveals a patchwork of color, and a new study now suggests it may be the first firm evidence of a protoplanet that formed early in the solar system and was later destroyed.
The stone belongs to the angrites, a rare group that makes up just 0.09 percent of the roughly 80,000 meteorites found on Earth. These rocks are among the oldest known, formed within a few million years of the solar system's birth 4.56 billion years ago, and they contain very little silica, a basic ingredient of most rocky worlds. For years, that shortage led scientists to assume angrites came from small asteroids.
The new paper, published July 1 in Earth and Planetary Science Letters, challenges that assumption. Its authors point to clinopyroxene in the meteorite, a mineral rich in aluminum that suggests formation under extreme pressure during a violent impact. Such pressures, they argue, could not have existed inside a small asteroid. The parent body would have had a radius of at least 1,000 kilometers, and possibly up to 1,800, making it comparable to the Moon or even Mars.
The proposed story is one of destruction: this embryonic world orbited the Sun, then collided with another body and broke into rubble. Some fragments eventually fell to Earth as angrites. "It's incredible to think there was once a world this large," said Aaron Bell, the study's lead author. "We only know it existed because a few fragments happened to land on Earth."
What the lost protoplanet might have become is still unknown, but the researchers suspect some of its material helped build other terrestrial planets, Earth included. For now, the claim depends on one meteorite, and the next test is whether other angrites carry the same signs.
In 2019, a rock was recovered from the Sahara Desert and given the catalog name NWA 12774. The letters stand for Northwest Africa, a label applied to every meteorite found in that region. Under cross-polarized light, a thin slice of it shows a patchwork of color. A new study now suggests the rock may be the first firm evidence of a protoplanet that formed in the early solar system and was later destroyed.
NWA 12774 belongs to a group called angrites. About 80,000 meteorites have been found on Earth so far, and angrites make up only 0.09% of them. They are also among the oldest rocks known in the solar system, having formed within a few million years of its beginning 4.56 billion years ago. Their chemistry is unusual too: they hold very little silica, or silicon dioxide, a main ingredient of most asteroids and rocky planets.
Because of that shortage of silica, scientists had previously guessed that angrites came from small asteroids. The new paper, published July 1 in Earth and Planetary Science Letters, challenges that view. The team points to clinopyroxene in NWA 12774, a mineral common in Earth's crust and mantle. This clinopyroxene is unusually rich in aluminum, which indicates it formed under extremely high pressure, possibly during a high-energy collision.
The researchers wrote that such pressures could not have built up inside a small asteroid. That puts the radius of the angrite parent body at no less than 621 miles (1,000 kilometers). The meteorite's sharp edges suggest it formed near the surface of that body, which would make the parent larger still, with a radius of up to 1,118 miles (1,800 km). For scale, Earth's moon has a radius of 1,080 miles (1,737 km), and Mars has 2,106 miles (3,390 km). The proposed "planetary embryo" could therefore have been as big as the moon or even Mars.
The scenario the authors describe is that this body orbited the sun and then crashed into another celestial body, shattering into rubble billions of years ago. Some of the debris eventually fell to Earth as angrite meteorites.
"It's incredible to think there was once [another] world this large," said Aaron Bell, the study's first author and a petrologist at the University of Colorado Boulder, in a statement. "We only know it existed because a few fragments of it happened to land on Earth." He added that the meteorites preserve evidence of a completely different pathway through which early planets developed.
If the angrites did come from a protoplanet, the world that might have grown from that embryo would probably have looked very different from today's rocky planets. Bell said the materials that formed the angrite parent body are fundamentally different from the ingredients of Earth and Mars, pointing to a distinct and separate evolutionary path in the early solar system.
What happened to the lost protoplanet is still unclear. The researchers speculate that some of its fragments may have become building blocks of other terrestrial planets, Earth among them. The claim rests on the interpretation of one meteorite's mineral chemistry, so the next test is whether other angrites show the same signs.
Citazioni salienti
It's incredible to think there was once [another] world this large. We only know it existed because a few fragments of it happened to land on Earth.— Aaron Bell, petrologist, University of Colorado Boulder
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