Fragment of an ancient world found in a meteorite from the Sahara

The meteorite in question is Northwest Africa 12774, or NWA 12774. It belongs to angrites - a very rare type of ancient volcanic meteorites. According to the University of Colorado at Boulder, among the more than 80,000 known meteorites on Earth, only 68 belong to the Angrites.

The main intrigue is that this meteorite, judging by the minerals inside it, did not form in a small asteroid. The pressure needed to form some of its crystals points to a much larger body - perhaps the size of the Moon or even close to Mars.

Details

Angrites have long interested planetologists because they are among the oldest volcanic rocks in the solar system. They formed just a few million years after its birth, meaning they retain information about a time when planets were just assembling from dust, rocks and larger bodies.

In the new study, scientists examined the mineral clinopyroxene inside meteorite NWA 12774. This is a crystal that is found in both the Earth's crust and mantle. In this meteorite, clinopyroxene turned out to be unusually rich in aluminium. Such a feature may suggest that the mineral was formed under very high pressure.

The researchers calculated how much pressure was needed to form these crystals. It turned out to be at least 17.5 kilobars. For comparison: the pressure at the bottom of the Mariana Trench - the deepest point of the ocean on Earth - about 1 kilobar. That is, the meteorite harbours traces of conditions far more extreme than those at the bottom of the ocean.

Such pressure could not have arisen inside a small asteroid. According to the authors' calculations, the parent body of angrites should have had a radius of at least about 1000 kilometres. And if the crystals formed not deep, and closer to the surface, the body itself could be even larger - a radius of more than 1800 kilometres. This is already comparable to the Moon.

Simply put, the small meteorite was like a fragment of a wall from a huge building that disappeared. The building itself is no longer there, but you can tell from the piece that it once existed and was much larger than previously thought.

Scientists do not know exactly how this ancient world died. One of the most likely versions is a powerful collision in the early solar system. After it, a large body may have split apart and its debris scattered and later became part of other bodies or hit Earth as meteorites.

Why it matters

This study shows that the early solar system was more complex than it seems. It may have had large embryo planets that did not survive to our time. Some became part of modern planets, others were destroyed, and their debris can still hit Earth today.

Most notably, the Angrites' parent body may not have evolved in the same way as Earth, Mars, or other rocky planets. The meteorite contains little silica, an important component of Earth's rocks. This means that large worlds with unusual chemical compositions and a different development path could have existed in the early solar system.

The discovery is also a reminder: meteorites are not just "rocks from space." Sometimes they are archives of vanished worlds. They can store traces of pressure, temperature and chemical processes that took place billions of years ago.

The background

Planets didn't appear immediately ready-made. In the early solar system, dust and rocky debris gradually coalesced into larger bodies. Some grew to the size of the Moon or Mars. Such objects are called planetary embryos, or protoplanets.

Some of these bodies became the building material for Earth, Venus, Mars and Mercury. Others collided, collapsed, or were ejected into other orbits. The modern planets are therefore only the surviving part of a much more chaotic early history.

Meteorite NWA 12774 provides a rare glimpse into this era. It does not show us the ancient world in its entirety, but it preserves minerals from which we can reconstruct conditions within its parent body.

Source

Thestudy is Aaron S. Bell et al, "High-pressure clinopyroxene in Northwest Africa 12774 and new geobarometric evidence for a planetary embryo-sized angrite parent body", Earth and Planetary Science Letters, 2026.