HWNEWS
A 65-Gram Angrite Recovered a Lost Mars-Sized World
A new pressure gauge read in a single Sahara meteorite rewrites the size of the angrite parent body, and gives the early solar system a new demolition derby.
A new pressure gauge read in a single Sahara meteorite rewrites the size of the angrite parent body, and gives the early solar system a new demolition derby.
The Angrite Parent Body was supposed to be small. For decades, planetary scientists treated it as a leftover chunk of rock from the early solar system: an asteroid less than 200 kilometers across, so small that its interior never melted, so cool that nothing inside it differentiated into crust, mantle, and core. The chemistry of angrites, the rare meteorite class named for the Brazilian town where the first specimen landed in 1869, seemed to demand that conclusion. They are silica-poor, dense, and uniform, the kind of rock you get from a body that never went through the violent unmixing that produced Earth, Venus, or Mars.
A new analysis of one 65-gram pebble, recovered from the Sahara in 2019 and catalogued as NWA 12774, forces a revision. According to research from the University of Colorado Boulder published in Earth and Planetary Science Letters, the parent body that produced this rock was large enough to differentiate. The minimum radius implied by the team's measurements is roughly 1,800 kilometers, about the size of the Moon. The upper estimate stretches to 3,300 kilometers, in the neighborhood of Mars. The work, led by A.S. Bell with coauthors L. Waters and M. Ghiorso at CU Boulder, is described in a University of Colorado Today press release dated June 1, 2026 and covered in detail by Universe Today. The peer-reviewed paper is available on ScienceDirect.
The instrument behind the revision is a geobarometer, a tool that infers the pressure at which a rock crystallized from the chemistry of its minerals. Geobarometers are common in petrology, but most of them are calibrated for the pressures found inside Earth. The CU Boulder team built a new one, called a CaTs-liquid geobarometer, that works on clinopyroxene crystals, a silicate mineral rich in calcium and magnesium. CaTs stands for Ca-Tschermak's component, the slot aluminum occupies when it substitutes into the crystal structure under high pressure. The more aluminum the crystal holds, the higher the pressure under which it grew.
NWA 12774 is unusually well suited to that reading. It is an angrite, and angrites are themselves rare: only about 68 of the roughly 80,000 meteorites catalogued on Earth are angrites, according to the Universe Today summary of the paper. The clinopyroxene crystals in this particular specimen are gem-quality, sharp-edged, and chemically pristine, which matters because diffusion would otherwise blur the original aluminum signal. Read through the new barometer, the crystals point to a crystallization pressure of 17.56 kilobars, more than 17 times the pressure at the bottom of the Mariana Trench.
Pressure alone does not give you a radius. A small body buried deep enough can in principle produce high pressure, and the team's analysis couples the pressure reading to a depth estimate derived from another clue: the sharpness of the crystal edges. Sharp edges imply rapid transport from depth to the surface, the kind of ejection that a volcanic-style eruption on a differentiated body would produce. The combined constraint puts the crystallization site somewhere in the upper 200 kilometers of the parent body's interior, which, in turn, fixes the body's minimum radius at about 1,800 kilometers and its upper bound near 3,300 kilometers.
That is a much larger object than the small undifferentiated asteroid the old story required. To put numbers next to the change: the old picture was a parent body smaller than 200 kilometers across. The new one is at least nine times that diameter, and possibly closer to 16 times. The parent body was, in other words, not a leftover fragment. It was a protoplanet, in the same size class as the Moon or Mars, and it went through the same geological unmixing that produced the modern terrestrial planets.
What happened to it? The CU Boulder team interprets the data as showing that the Angrite Parent Body was destroyed by a giant impact during the chaotic first hundred million years of the solar system. Most of its mass, the paper's authors argue, was likely re-accreted into the growing Earth and the other inner planets. This is a familiar story for planetary scientists, who have long argued that the early solar system was less a clean assembly line than a demolition derby, with protoplanets colliding, merging, and being stripped down to feed larger bodies. The new result pushes that picture further: even protoplanets that never made it into the final census of planets can leave survivors.
The honest limit of the finding is what the data constrain and what they do not. The pressure reading fixes the size class of the parent body. It does not fix the body's composition in detail, nor does it place the body in a particular orbit. To call the Angrite Parent Body "Mars-like" or "another Mars" would be a category error: it is Mars-sized, not Mars-like, and treating inferred size as inferred identity erases the part of the claim that is not yet supported. The paper itself, as summarized by Universe Today, stops short of identifying the Angrite Parent Body with any specific known body in the solar system today.
What the result does support is a method. Geobarometry on rare, well-preserved meteorites is a way of recovering destroyed worlds from crystals smaller than a fingernail. NWA 12774 is the second angrite to yield a high-pressure clinopyroxene reading in recent years, and the consistency of those readings, in independent labs, is the kind of cross-check that turns a single measurement into a working hypothesis. If the picture holds, the inventory of the early solar system will need to grow: not just the planets that survived, but the protoplanets that did not, and whose surviving fragments are already in museum drawers waiting to be re-read.