Rare Meteorite Reveals Evidence of a Lost Moon-Sized Planetary Embryo

Evidence of a Planetary Embryo

The meteorite, known as Northwest Africa 12774 (NWA 12774), belongs to a rare class of volcanic meteorites called angrites. Space.com reported that only 68 angrites are known among more than 80,000 recovered meteorites.

Researchers Aaron S. Bell, Laura Waters, and Mark Ghiorso used geobarometry to analyze the mineral chemistry of aluminium-rich clinopyroxene within the rock. They estimated a formation pressure of at least 17.5 kilobars. The authors argue that this pressure is too high for a small asteroid, suggesting instead a parent body on the scale of a planetary embryo.

The study notes that the crystals in NWA 12774 preserve chemical patterns and sharp edges, indicating they were not buried in a hot planetary interior for a long period. To reconcile high pressure with a lack of prolonged heating, the researchers interpret that the parent body must have been large enough to generate intense pressure closer to its surface.

Scale and Origin

While the study does not identify a specific named planet, Space.com reported that under one scenario, the parent body may have exceeded approximately 1,800 kilometers in radius. This would make the body comparable in size to the Moon or potentially approaching the size of Mars.

Such a body may have been broken apart, absorbed into larger planets, or reduced to fragments during the violent assembly of the inner solar system. This aligns with research on hit-and-run planetary collisions, such as a 2006 Nature paper by Erik Asphaug, Craig Agnor, and Quentin Williams, which established that large impacts do not always result in mergers.

The significance of NWA 12774 is further supported by previous research. A 2024 paper in Geochimica et Cosmochimica Acta treated the meteorite as a record of mantle heterogeneity, indicating it underwent volcanic and chemical processing on a body large enough to melt and separate materials. Additionally, a 2022 paper in Geochimica et Cosmochimica Acta by Francois Tissot and colleagues argued that the angrite parent body may represent a large, chemically distinctive early planetesimal.

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