A lost planetary embryo, potentially as large as the moon or Mars, shattered 4.5 billion years ago after colliding with another celestial body. Scientists confirmed the existence of this protoplanet by analyzing the Northwest Africa (NWA) 12774 angrite meteorite, which contains high-pressure mineral signatures inconsistent with small asteroids. According to research published in Earth and Planetary Science Letters, this discovery suggests the early solar system contained diverse, large-scale worlds that contributed to the building blocks of modern terrestrial planets.
What is an angrite meteorite?
Angrites are rare volcanic rocks that formed within the first few million years of the solar system’s history, roughly 4.56 billion years ago. Out of more than 80,000 meteorites recovered on Earth, only 68 are classified as angrites, according to data from the University of Colorado Boulder. Unlike the rocky material found on Earth or Mars, these meteorites contain remarkably low levels of silica. Because of this chemical profile, planetary scientists previously assumed these rocks originated from small asteroids with radii of less than 200 kilometers.
The pressure required to form the minerals in NWA 12774 is 17.5 kilobars. For context, the Mariana Trench, the deepest point on Earth, experiences pressure of only about 1 kilobar.
How did scientists identify the lost protoplanet?
Aaron Bell, an assistant research professor at the University of Colorado Boulder, and his colleagues identified the protoplanet by examining clinopyroxene crystals within the NWA 12774 meteorite. These crystals are rich in aluminum, a geochemical signature that indicates formation under intense, deep-seated pressure. By reconstructing these conditions, the team determined the parent body must have possessed a radius of at least 1,000 kilometers—and potentially as large as 1,800 kilometers.
This size estimate exceeds the dimensions of any known asteroid. The preservation of sharp-edged crystal patterns further suggests these minerals formed at relatively shallow depths within a massive body, reinforcing the theory that the parent object was a planetary embryo rather than a small, inert rock.
Why does this discovery change planetary formation models?
The chemical composition of NWA 12774 suggests that the early solar system was home to bodies with evolutionary paths distinct from those of Earth and Mars. While current terrestrial planets share similar building materials, the angrite parent body suggests a different, separate history. According to Bell, this implies that the solar system’s early debris field included a variety of protoplanetary embryos that were eventually destroyed, with their fragments potentially serving as the raw material for the planets we see today.
Pro Tips for Identifying Meteorites
- Density: Meteorites are typically much denser than common Earth rocks.
- Magnetic Signature: Many meteorites, particularly those containing iron-nickel, will attract a magnet.
- Fusion Crust: Look for a thin, dark, glassy coating caused by the rock melting during its descent through the atmosphere.
Frequently Asked Questions
- How many angrite meteorites have been found?
- Only 68 angrites have been identified out of more than 80,000 meteorites discovered on Earth.
- Why were scientists surprised by the pressure findings?
- The high concentration of aluminum in the clinopyroxene indicated pressure levels 17 times greater than those at the bottom of the Mariana Trench, which is impossible for a small asteroid.
- Could there be more lost protoplanets?
- Yes. According to Aaron Bell, many meteorites housed in museum or university collections remain unstudied, likely hiding evidence of other ancient, shattered worlds.
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