A Rare Meteorite Hints at a Lost Planet, but Scientists Aren’t Certain

A 454-gram rock pulled from the Sahara Desert is now the strongest physical case yet that a Moon-sized world once circled the young Sun, then vanished. Researchers at the University of Colorado Boulder say the stone, formally catalogued as Northwest Africa 12774 (NWA 12774), preserves mineral pressures that no small asteroid could ever generate. The study appeared this year in the journal Earth and Planetary Science Letters.

Independent meteoriticists call the underlying math sound. None of them call the missing planet proven, and the paper itself stops short of that claim too.

The Sahara Rock That Broke an Old Assumption

NWA 12774 turned up in the Sahara Desert in 2019, most likely in Mauritania, and passed through the region’s meteorite trade before researchers formally classified it as an angrite. The Meteoritical Bulletin entry lists it as a 454-gram stone with green crystals set in a dark matrix, barely bigger than a fist.

Angrites are volcanic meteorites, among the oldest igneous rocks known anywhere in the solar system. They formed within a few million years of the solar system’s birth roughly 4.56 billion years ago. They are also extraordinarily rare. Of more than 80,000 meteorites recovered on Earth, only 68 are angrites.

What makes them strange is their chemistry. Angrites carry very little silica, the ingredient that dominates Earth, Mars and nearly every other rocky planet. For decades that quirk supported a tidy explanation: a small asteroid under 200 kilometers (124 miles) across could melt early, separate into layers and send fragments toward Earth, all without requiring any large missing world.

Word of NWA 12774’s stranger pedigree has already circulated among astronomy watchers online. The SETI Institute, a research nonprofit devoted to the search for extraterrestrial intelligence, told followers the crystal chemistry points to a protoplanet about 1,800 kilometers across, framing the rock as a rare planetary science curiosity worth watching.

How Scientists Read Pressure in a Crystal

The tell was a mineral called clinopyroxene, a crystal common in rocky planets and their crusts. Finding it inside an angrite at all was unusual. Finding it packed with aluminum was the real surprise, since that chemistry typically only forms under crushing pressure.

Lead author Aaron Bell, an assistant research professor in the Department of Earth Science at CU Boulder, and colleagues Laura Waters and Mark Ghiorso spent about a year building and testing a computer model, a geobarometer tailored specifically to angrite chemistry, because standard clinopyroxene pressure tools do not work on rocks this chemically odd.

According to the University of Colorado Boulder, whose team calculated pressures of at least 17.5 kilobars, the aluminum-rich crystals could not have formed inside a small asteroid. A more detailed run of the model put the range between 14.8 and 18.3 kilobars, averaging 17.56. For comparison, the crushing pressure at the bottom of the Mariana Trench, the deepest point on Earth, is only around 1 kilobar. Whatever produced this rock endured more than 17 times that.

“It’s incredible to think there was once a world this large,” Bell said in the university statement. “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.” There’s a beauty, Bell has said elsewhere, in following that chain of reasoning, from atomic scale to lost world.

From Asteroid-Sized to Moon-Sized in One Calculation

That pressure number ruled out a small asteroid on its own. A second clue in the rock pushed the estimate even further.

The crystals inside NWA 12774 still have sharp edges and delicate chemical zoning. Both features tend to smear or vanish when a mineral spends a long time cooking deep inside a large, hot body. Since the edges survived, researchers concluded the crystals most likely formed close to the parent body’s surface. Pairing a shallow formation depth with 17.5 kilobars of pressure only works if the whole body is enormous, heavy enough to bear down hard even near its outer shell.

The paper, titled High-Pressure Clinopyroxene in Northwest Africa 12774 and posted online in April before CU Boulder publicized it in June, lays out that math across several scenarios. Here is how the size estimate climbed as each new constraint was applied:

Even the floor of that range breaks the old model. The ceiling puts a body once orbiting the young Sun in the same size class as a modern planet, before anything shattered it.

Did the Solar System Lose a Planet?

Probably, in the sense that a body this size likely existed and broke apart, though not in any confirmed, textbook sense. The pressure evidence is strong and the model is new, but outside experts differ on how much weight one meteorite can carry. This is one study, not settled consensus.

• Carl Agee, University of New Mexico meteoriticist: calls it “a very sound study” but says researchers have not “proven beyond a shadow of a doubt” that a body this large existed, even though “this one particular angrite seems to be consistent with that idea.”
• Francois Tissot, California Institute of Technology (Caltech) geochemist: finds the timescale remarkable, saying “this means that, within four million years, you’re making things that are the size of the moon. It’s a very, very rapid formation timescale.”
• William Bottke, Southwest Research Institute scientist: argues the fragments could simply have scattered into the asteroid belt and rained down as angrites for eons, with no need to fold any of it into today’s terrestrial planets.

Bottke’s alternative matters because it does not require the missing world to have contributed material to Earth at all. Tissot, who was not involved in the new paper but has separately argued for a large angrite parent body since 2022, still cautions that confirming evidence will be hard to gather. “We’re entering a new era, and there is a lot to be confirmed,” he has said.

What the Study Doesn’t Show

Strip away the drama and the paper is narrower than the headlines suggest. Several things it explicitly does not do:

• It does not identify the lost body’s orbit or confirm where in the solar system it formed.
• It does not show that the object, or any piece of it, struck Earth directly.
• It does not connect NWA 12774 to the separate impact that formed Earth’s Moon.
• It does not prove that every angrite in collections came from the same Moon-sized body.

The evidence is mineralogical and model-based, drawn from a single rare rock whose parent body was already difficult to reconstruct before this paper existed.

The Next Lost World Might Be Sitting in a Drawer

NWA 12774 had already drawn scientific attention before this pressure work. A 2024 paper in Geochimica et Cosmochimica Acta examined the same Cr-rich quenched angrite and read it as a record of mantle heterogeneity inside the angrite parent body, evidence the rock had passed through real volcanic processing rather than forming from primitive dust.

Other researchers have hunted for the parent body from a different angle entirely. A 2024 study ran spectral comparisons against known asteroids and found no convincing match. Candidate asteroids such as Eureka and Robinson turned out to be far smaller than the proposed parent body, and Eureka was later linked to debris from Mars instead. Between weak spectral matches and now a pressure signature too high for anything asteroid-sized, the case for a vanished, larger world keeps gaining ground from more than one direction.

Reconstructing a body nobody has ever seen from mineral chemistry alone is a familiar kind of exercise in planetary science. It works on the same instinct as models that push Earth’s own future outward, including one recent estimate putting the outer limit for plant life on Earth at 1.87 billion years from now, long before the Sun itself becomes the real threat.

Bell says the bigger lesson sits in museum drawers, not in this one meteorite. “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,” he said. Scientists still do not know exactly how this one met its end. A collision remains the leading guess, its fragments scattered and, perhaps, folded into the very planets that survived it.

Frequently Asked Questions

What Does NWA Stand for in the Meteorite’s Name?

NWA stands for Northwest Africa, a designation given to every meteorite recovered from that broad region regardless of the exact country. NWA 12774 was found in the Sahara Desert in 2019 and later catalogued through the Meteoritical Bulletin as a 454-gram angrite.

What Exactly Made This Meteorite’s Crystals Unusual?

The aluminum in NWA 12774’s clinopyroxene was concentrated in a specific component called calcium Tschermak’s molecule, a chemical signature that only forms under high pressure. That precise marker, rather than just elevated aluminum in general, is what let Bell’s team calculate an exact pressure figure instead of a rough guess.

Does This Mean Earth’s Moon Came from the Same Lost World?

No. Earth’s Moon is thought to have formed from a separate, Mars-sized impactor that struck proto-Earth when our planet was between 60 million and 140 million years old, a different and far better documented collision. The NWA 12774 study does not link its vanished body to that event.

Did Scientists Just Discover a Ninth Planet?

No. The solar system’s eight recognized planets are unchanged. The body described in this study, if it existed, only lasted through the solar system’s first several million years and never survived long enough to be classified as a planet at all.

What Other Angrites Are Scientists Comparing NWA 12774 To?

Researchers studying the angrite parent body have also examined other known angrites, including D’Orbigny, Angra dos Reis and Northwest Africa specimens such as NWA 7203 and NWA 12320. Each carries its own mineral record, helping test whether one giant parent body, or several smaller ones, produced the whole group.