Ancient Planet Fragment May Have Fallen to Earth as Desert Meteorite
A meteorite discovered in the Sahara Desert in 2020 contains mineral fragments that scientists say may originate from a protoplanet that formed in the early Solar System, according to research published in the journal Nature Communications and confirmed by the University of New Mexico and the California Institute of Technology.
The 70-gram meteorite, designated Northwest Africa 13988, was found among other space rocks in the Moroccan desert and initially classified as an achondrite—a rare type of stony meteorite lacking chondrules, the tiny spherical mineral grains common in most meteorites. However, further analysis revealed its composition included aluminum-rich inclusions (CAIs), the oldest known solids in the Solar System, dating back to the first two million years after the Sun’s formation.
Why does this meteorite stand out among others?
Unlike most meteorites, which typically originate from the asteroid belt or Mars, Northwest Africa 13988’s chemical signature suggests it may have broken off from a much larger body—one that existed during the chaotic early phase of planetary formation. “This meteorite is a window into the building blocks of the planets,” said Dr. Poorna Srinivasan, a planetary scientist at the University of Arizona and lead author of the study. “It’s like holding a piece of the primordial Solar System in your hand.”
Researchers compared its isotopic ratios of titanium and calcium to those found in other meteorites, including those from the Vesta asteroid and the Allende meteorite. The data showed Northwest Africa 13988’s composition did not match any known parent body, reinforcing the hypothesis that it came from a distinct, now-extinct protoplanet.
What does this discovery tell us about the early Solar System?
Scientists estimate that within the first 10 million years of the Solar System’s existence, numerous planetesimals—small celestial bodies—collided and merged to form the planets we recognize today. Most evidence of these early collisions has been erased by geological activity or destroyed in subsequent impacts. However, the mineral composition of Northwest Africa 13988 suggests it may preserve traces of such a protoplanet, which would have been roughly the size of Ceres, the largest object in the asteroid belt.
According to Dr. Kevin McKeegan, a cosmochemist at Caltech and co-author of the study, the meteorite’s CAIs “are like time capsules.” These inclusions formed at extremely high temperatures in the solar nebula and were later incorporated into the protoplanet before being ejected into space during a catastrophic impact. The fragments eventually made their way to Earth, landing in the Sahara after being dislodged from a larger asteroid.
How does this compare to other protoplanetary discoveries?
While no other meteorite has been definitively linked to a protoplanet, previous studies have identified fragments that may have originated from similar early bodies. For example, the Angra dos Reis meteorite, found in Brazil, contains evidence of a differentiated parent body with a metallic core and silicate mantle—hallmarks of a protoplanet. However, Northwest Africa 13988 stands out due to its unique combination of CAIs and achondritic texture, which suggests a more complex formation history.
A 2022 study in Science Advances proposed that some meteorites from the Eucrite group could also trace back to a lost protoplanet, but those samples lacked the ancient CAIs found in Northwest Africa 13988. “This meteorite is a missing piece in the puzzle of planetary formation,” said Dr. Meenakshi Wadhwa, director of the School for Exploration and Planetary Sciences at Arizona State University. “It bridges the gap between what we know about the earliest Solar System and the planets that eventually formed.”
What happens next in the research?
The study’s authors plan to conduct further isotopic analyses to refine their understanding of the protoplanet’s composition. They are also collaborating with the NASA Lunar Sample Laboratory to compare Northwest Africa 13988 with lunar samples collected during the Apollo missions, which may share similar ancient origins.
Meanwhile, meteorite hunters in the Sahara continue to scour the desert for additional fragments, as even a small piece could provide new insights. “Every new meteorite is a potential treasure trove,” said Dr. Carl Agee, director of the Institute of Meteoritics at the University of New Mexico. “We’re still uncovering the secrets of our cosmic neighborhood.”
The discovery underscores the ongoing role of meteorites in rewriting our understanding of planetary formation. While the protoplanet itself is long gone, its fragments offer a rare glimpse into the violent and dynamic early days of the Solar System.