A rare meteorite discovered in the Sahara Desert, known as NWA 12774, provides the first definitive evidence of a massive, long-lost protoplanet that existed in the early solar system. According to research published in Earth and Planetary Science Letters, this space rock suggests the existence of a planetary embryo as large as the moon or Mars that shattered billions of years ago.
Evidence of a Lost Protoplanet
The Northwest Africa (NWA) 12774 meteorite belongs to a group of rocks called angrites. These are among the oldest volcanic materials in the solar system, forming within just a few million years of its origin approximately 4.56 billion years ago. While more than 80,000 meteorites have been identified on Earth, angrites remain exceptionally rare, with only 68 classified as such.
According to Aaron Bell, an assistant research professor in the Department of Earth Science at the University of Colorado Boulder, the unique chemical composition of these fragments indicates they originated from a body far larger than previously assumed. Scientists once theorized that angrites formed on small asteroids with radii of less than 200 kilometers (124 miles). However, the new analysis of NWA 12774 challenges this, suggesting the parent body possessed a radius of at least 1,000 kilometers (621 miles).
Why the Chemistry Matters
What distinguishes NWA 12774 from other rocky planets is its low silica content. Silica is a primary ingredient in terrestrial planets like Earth and Mars, yet it is significantly lacking in angrites.
The meteorite contains clinopyroxene, a mineral rich in aluminum that typically forms under the intense pressure found in the interior of a large world. The presence of this mineral, combined with the rock’s structural features, suggests a planetary-scale origin. Researchers conclude that the parent body may have had a radius reaching up to 1,800 kilometers (1,118 miles). For context, Earth’s moon has a radius of approximately 1,737 kilometers (1,080 miles).
Evolutionary Paths in the Early Solar System
This discovery implies that the early solar system hosted a diverse array of planetary embryos with evolutionary paths distinct from those of our current planets. The materials that constituted this lost protoplanet differ fundamentally from the building blocks of Earth and Mars.
Scientists suggest that after this massive body orbited the sun, it likely collided with another celestial object, shattering into the debris that eventually reached Earth. While the ultimate fate of this protoplanet remains a subject of study, researchers speculate that its fragments may have contributed to the formation of other terrestrial planets in the early solar system.
Key Takeaways
- Classification: NWA 12774 is an angrite, a rare type of volcanic meteorite that accounts for a tiny fraction of all known meteorite finds.
- Size Estimates: Based on high-pressure mineral indicators, the parent protoplanet likely had a radius between 1,000 and 1,800 kilometers.
- Scientific Significance: The study, published in Earth and Planetary Science Letters, provides evidence of a planetary embryo that followed an evolutionary path separate from the terrestrial planets we know today.
- Current Understanding: The findings shift the scientific consensus away from the theory that angrites originated from small asteroids, pointing instead toward a much larger, lost world.