A meteorite found in the Sahara Desert is giving scientists a rare look at a world that may no longer exist. By studying the chemistry of the 4.5-billion-year-old rock, researchers found evidence suggesting it formed inside a large protoplanet that was later destroyed during the chaotic early years of the solar system.
The meteorite, known as NWA 12774, belongs to the angrite family, one of the rarest groups of meteorites ever discovered. A new study published in Earth and Planetary Science Letterssuggests its parent body was far larger than the asteroids scientists had previously linked to angrites.
Meteorites are often described as time capsules from the birth of the solar system. Unlike planets, which have undergone billions of years of geological change, many meteorites still preserve traces of the conditions in which they formed. As reported by a press release shared by theUniversity of Colorado Boulder, NWA 12774 is a particularly unusual specimen.
Only 68 angrites have been identified among the roughly 80,000 meteorites found on Earth. Because they are so rare, each new analysis has the potential to reveal something new about the first few million years after the solar system formed.
A Rare Rock With An Unexpected Signature
When scientists examined NWA 12774, they found something that did not fit neatly with previous ideas about angrites. These meteorites contain very little silica, a major ingredient in rocky planets such as Earth. For that reason, researchers had generally assumed they came from relatively small asteroid-like bodies. The new study found evidence of clinopyroxene, a mineral commonly found in Earth’s crust and mantle.
More interestingly, the crystals contained unusually high levels of aluminum. Aaron S. Bell, an Earth scientist at the University of Colorado Boulder and a co-author of the study, explained that:
“The materials that formed the angrite parent body are fundamentally different from the ingredients of Earth and Mars. It points to a distinct and separate evolutionary path in planetary formation in the early history of our solar system.” That raised a key question: what kind of object could generate those conditions?
Reconstructing an Ancient World
To answer that question, the research team developed a computer model capable of estimating the pressure needed to form the crystals found in the meteorite. The research team explained that the process of developing and testing the model took about a year.
The results, published in the journal Earth and Planetary Science Letters, were striking. The team calculated that NWA 12774 formed under pressures of at least 17.5 kilobars. For comparison, the pressure at the bottom of the Mariana Trench, the deepest point in Earth’s oceans, is about one kilobar.
Those results suggested that the meteorite could not have formed within a small asteroid. Instead, its parent body would have needed to be significantly larger to generate such high internal pressures. The finding challenges the traditional view of angrites and points to a planetary body that experienced substantial growth early in its history.
Clues To A Vanished Protoplanet
Using their pressure estimates, the researchers concluded that the meteorite’s parent body must have been at least 1,200 miles in diameter. The actual size may have been even greater. The clue comes from the crystals themselves. The mineral grains inside NWA 12774 have sharp edges that likely would not have survived if they had formed deep beneath the surface.
Based on the study, this suggests the rock formed relatively close to the exterior of its parent body. If that was the case, the object could have been closer in size to the Moon, which is about 2,200 miles across, and possibly even approached the size of Mars.
“This means that, within four million years [of the solar system’s formation], you’re making things that are the size of the moon,” he added. “It’s a very, very rapid formation timescale.”
Scientists still do not know what happened to the proposed protoplanet. The researchers suggest it may have been shattered during collisions in the early solar system, with its fragments later becoming part of Earth and other rocky planets.
