A meteorite fragment reveals the existence of a giant planet that disappeared at the dawn of our solar system

The Secret Buried in the Sands of the Sahara

Four and a half billion years ago, a massive world orbited our Sun before colliding with another celestial body and disintegrating into a multitude of fragments. The existence of this planetary embryo, or protoplanet, has just been formally established thanks to a rock fragment discovered in the Sahara Desert. Known as Northwest Africa (NWA) 12774, this mineral remnant has allowed a team of researchers to piece together a forgotten chapter in the formation of our solar system.

According to information published by Yvaine Ye on behalf of the University of Colorado at Boulder, this discovery challenges traditional hypotheses about planetary evolution. Aaron Bell, an assistant research professor in the university’s Department of Earth Sciences, highlights the significance of this finding. “It’s incredible to think that a world of such size ever existed,” says the researcher. “We know it existed only because a few fragments happened to land on Earth. These meteorites have preserved evidence of a completely different trajectory along which the early planets developed.”

Titanic Pressure Revealed by a Crystal

A detailed analysis of the NWA 12774 meteorite by Aaron Bell and his colleagues revealed the presence of a specific mineral crystal: clinopyroxene. While this element is commonly found in Earth’s crust and mantle, the variant identified in this extraterrestrial fragment stood out due to its exceptionally high aluminum content. This chemical characteristic is an indisputable indicator of subterranean formation under extreme conditions.

To understand the origin of this rock, the researchers modeled the conditions necessary for its formation. Their calculations showed that this aluminum-rich clinopyroxene required a minimum pressure of 17.5 kilobars to crystallize. To put this figure in perspective, the colossal pressure at the bottom of the Mariana Trench—the deepest point in Earth’s oceans—reaches only about 1 kilobar.

Such crushing force cannot physically occur inside a small space object. Analysis of these pressures led researchers to conclude that the celestial body containing the original rock must have had a radius of at least 1,000 kilometers, or 621 miles.

The Unexpected Dimensions of a Planetary Embryo

The meteorite contained other clues that led scientists to revise the size of this lost world upward. The crystals trapped inside NWA 12774 have retained sharp edges as well as particularly delicate chemical patterns. If these elements had formed in the planet’s abyssal depths, these characteristics would inevitably have been erased by heat and internal dynamics.

This preservation indicates that the crystals actually formed at relatively shallow depths within their parent body. For a pressure of 17.5 kilobars to be reached near the surface, the object’s total mass must have been enormous. Modeling thus suggests that this protoplanet could have had a radius exceeding 1,800 kilometers (1,118 miles), which is roughly the size of our Moon.

In the upper estimate, this vanished world might even have approached the size of Mars, which has a radius of 3,300 kilometers (2,050 miles). This conclusion overturns previous theories. Until now, the scientific community believed that this type of meteorite invariably originated from asteroids with a radius no greater than 200 kilometers, or 124 miles.

The Chemical Enigma of the Angrites

The NWA 12774 meteorite belongs to an extremely rare family of space rocks called angrites. These fragments are considered the oldest known volcanic rocks in our solar system. They formed within just a few million years after the solar system’s birth, approximately 4.56 billion years ago. Their rarity is striking: out of more than 80,000 meteorites recorded on Earth’s surface, there are only 68 angrites.

What particularly baffles researchers is the chemical composition of these samples. Unlike Earth, Mars, or the other rocky planets we know of, angrites contain a minuscule amount of silicon dioxide, or silica. Yet this compound is a major and fundamental component of nearly all the terrestrial planets identified in our solar system.

A Cosmic Family Tree in Need of Rewriting

The exact fate of this giant protoplanet remains shrouded in mystery. Scientists speculate that a catastrophic event during the early days of the solar system may have shattered it. The fragments resulting from this destruction would then have traveled through space, potentially becoming the building blocks for the formation of other terrestrial planets, including Earth.

This discovery opens up new avenues for space research. “There are many meteorites sitting in drawers that haven’t been studied in depth, so there have probably been other protoplanets of this type that we don’t know about,” explains Aaron Bell. The scientist emphasizes the uniqueness of this object: “The materials that formed the parent body of the angrites are fundamentally different from the ingredients of Earth and Mars. This points to a distinct and separate evolutionary path in planetary formation early in the history of our solar system.”

The detailed results of this research have been documented in a paper co-authored by Aaron S. Bell and his team, titled “High-Pressure Clinopyroxene in Northwest Africa 12774 and New Geobarometric Evidence for a Planetary-Embryo-Sized Parent Body of the Angrites.” The study is published in the 2026 issue of the journal Earth and Planetary Science Letters and is accessible via its digital object identifier (DOI: 10.1016/j.epsl.2026.120029).

According to the source: phys.org

A meteorite fragment reveals the existence of a giant planet that disappeared at the dawn of our solar system