A fragment of NWA 12774, a meteorite found in the Sahara Desert, has given scientists their first definitive proof that a lost world roughly the size of the moon once orbited our sun 4.5 billion years ago. Researchers led by Aaron Bell, an assistant research professor in the Department of Earth Science at the University of Colorado Boulder, discovered that this ancient protoplanet—and possibly several others like it—shattered early in the solar system's history, with its fragments perhaps becoming the raw material for planets we know today, including Earth.
For decades, scientists held a firm assumption: the unusual volcanic rocks known as angrites could only come from small asteroids. These meteorites are extraordinarily rare—only 68 of more than 80,000 meteorites discovered on Earth are angrites—and they contain almost no silicon dioxide, the fundamental ingredient in nearly every terrestrial planet. That chemical oddity seemed to rule out their origin from anything large. But when Bell's team examined NWA 12774 under close scrutiny, they found something unexpected: the meteorite contained aluminum-rich clinopyroxene, a mineral commonly found on Earth that requires colossal pressure to form.
The numbers told a startling story. The aluminum-rich clinopyroxene inside NWA 12774 needed at least 17.5 kilobars of pressure—a crushing weight comparable to 17,500 times Earth's atmospheric pressure. To put that in perspective, the deepest ocean trench on Earth, the Mariana Trench, exerts only about 1 kilobar of pressure. Such extreme conditions could never exist inside a small asteroid. The researchers' calculations revealed that the parent body had to be at least 1,000 kilometers in radius, roughly the size of Earth's moon.
But that was only the beginning. The team noticed something equally remarkable: the crystals inside the meteorite still held sharp edges and delicate chemical patterns that would have been obliterated if they'd formed deep underground under such intense pressure. This suggested the crystals likely crystallized at shallower depths, which meant the parent body had to be even larger. Based on this evidence, the protoplanet may have extended to 1,800 kilometers in radius—comparable to the moon's size and possibly approaching Mars, which has a radius of 3,300 kilometers.
The discovery fundamentally challenges our understanding of how planetary systems form. "The materials that formed the angrite parent body are fundamentally different from the ingredients of Earth and Mars," Bell explained. "It points to a distinct and separate evolutionary path in planetary formation in the early history of our solar system." Rather than following one pathway to planet formation, the young solar system apparently experimented with multiple recipes, creating worlds of different compositions that met different fates.
What happened to this lost world remains a mystery. It may have collided with another celestial body and fragmented, with its debris scattered throughout the solar system. Some of those fragments eventually made their way to Earth, where they waited billions of years in desert sand until scientists found them. Bell notes that countless meteorites still sit unstudied in research drawers worldwide, suggesting that evidence of other vanished protoplanets may be waiting to reveal the solar system's hidden history.