Our Solar System may once have hosted an additional planet that no longer exists.This long-vanished world could have been nearly as large as Mars before meeting a catastrophic fate.We might never have known it existed at all—if not for fragments that eventually made their way to Earth.
About 4.56 billion years ago, the early Solar System was a chaotic field of violent collisions, where countless rocky bodies were still forming and crashing into one another.
A recent study now adds evidence that among these early objects was a Moon-to-Mars–sized “planetary embryo” that has since disappeared.
“It’s incredible to think there was once a world this large,” said Aaron Bell, an experimental petrologist at the University of Colorado Boulder and lead author of the study. “We only know it existed because a few fragments of it happened to land on Earth.”
One such fragment is the NWA 12774 meteorite, a small half-kilogram rock found in 2019 in the Sahara Desert. It contains a dark matrix filled with olivine crystals, a common mineral also found in Earth’s mantle.
NWA 12774 belongs to an extremely rare class of meteorites known as angrites, which make up just a tiny fraction of all known meteorite finds. These rocks are among the oldest igneous materials ever discovered, formed only a few million years after the Solar System began to solidify.
Scientists believe angrites came from a larger parent body—known as the angrite parent body (APB)—but its true size has long been debated.
Because angrites are unusually low in silica, some researchers have suggested the APB may have been a relatively small asteroid, perhaps up to 200 kilometers in radius, similar to large bodies like Vesta in the asteroid belt.
However, Bell notes that “the materials that formed the angrite parent body are fundamentally different from the ingredients of Earth and Mars,” suggesting a distinct evolutionary path in early planetary formation.
Other studies have argued the opposite: that the APB may have been a much larger, planet-like body, based on evidence of significant internal melting and volcanic activity.
To investigate further, researchers analyzed NWA 12774 in detail using electron microprobe techniques and high-resolution X-ray mapping. They also developed a new geobarometric model to estimate the pressure conditions under which the meteorite formed.
Their results showed that the rock contains aluminum-rich clinopyroxene crystals, which only form under high-pressure environments—conditions unlikely in small asteroids.
This suggests the meteorite likely originated deep within a much larger, planet-sized body.
Using pressure estimates, core mass modeling, and mantle density calculations, the team concluded that the APB must have had a minimum radius of about 1,000 kilometers.
However, the crystal textures—remarkably well preserved—indicate formation in a relatively shallow magma reservoir, implying an even larger body.
In that case, the APB may have reached a radius of around 1,800 kilometers, slightly larger than Earth’s Moon. Some upper estimates even place it near 3,300 kilometers, just under the size of Mars.
What ultimately destroyed this ancient world remains unknown. One possibility is that early Jupiter, still forming and migrating, may have played a role in destabilizing it.
Whether it was shattered by a massive collision or torn apart by gravitational forces, its fragments were scattered across the Solar System—some eventually landing on Earth, where they offer rare clues to its existence.
Researchers suggest there may be more such lost worlds yet to be identified, hidden in meteorite collections waiting for closer study.
“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.
The study was published in Earth and Planetary Science Letters.
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