They are similar enough that we feel confident they came from the same parent body
Across billions of kilometers and billions of years, three asteroids now speak a common chemical language — one that points back to a single violent birth in the early solar system. New observations from the James Webb Space Telescope suggest that Bennu and Ryugu, both recently visited by sample-return missions, are fragments of the same ancient parent body that also produced 142 Polana, the largest surviving remnant of a primordial collision. In reading the spectral signatures of these distant rocks against physical samples returned to Earth, scientists are learning that the solar system's family trees are written not in biology, but in carbon and iron oxide scattered across the void.
- A long-suspected cosmic kinship between two of the most closely studied asteroids in history now has its strongest chemical evidence yet.
- The subtle but real differences in surface composition between Bennu, Ryugu, and 142 Polana created tension in the shared-origin theory — threatening to unravel what seemed like a tidy family portrait.
- Researchers resolved the tension by pointing to time itself: proximity to the sun and billions of years of micrometeoroid bombardment have weathered each fragment differently since their violent separation.
- The study, published in The Planetary Science Journal, stops short of certainty — but positions a common parent asteroid as the most coherent explanation for why three rocks, scattered across the solar system, carry the same chemical fingerprint.
Two asteroids that have each hosted robotic visitors from Earth — Bennu and Ryugu — may be ancient siblings, born from the same catastrophic collision that shook the early solar system. New data from the James Webb Space Telescope now lends compelling weight to that idea, suggesting both are fragments of a single massive parent body that also produced 142 Polana, the largest surviving piece of a shattered asteroid family.
Bennu, roughly 500 meters wide, was sampled by NASA's OSIRIS-REx mission, which returned material to Earth in September 2023. Ryugu, slightly larger at around 900 meters, was explored by Japan's Hayabusa2, with samples arriving in December 2020. Both spin like tops and are classified as potentially hazardous, though neither poses a meaningful threat for at least a century.
In a study published August 18 in The Planetary Science Journal, researcher Anicia Arredondo and colleagues at Southwest Research Institute compared JWST spectroscopy of 142 Polana — a 55-kilometer rock orbiting the main asteroid belt — against the physical samples returned from Bennu and Ryugu. The match was striking: all three share the same core ingredients, carbon and magnetite, a rare form of iron oxide.
The slight compositional differences between them do not undermine the theory — they enrich it. Bennu and Ryugu orbit far closer to the sun than Polana, leaving their surfaces more exposed to solar radiation and particle bombardment. Polana, meanwhile, has endured its own billions of years of micrometeoroid weathering. Each rock has been quietly rewritten by time and environment since the original fragmentation.
"They are similar enough that we feel confident that all three asteroids could have come from the same parent body," Arredondo said. The conclusion is not yet absolute, but the chemical resemblance across three distant worlds offers the most coherent story yet of how one ancient collision echoes across the solar system to this day.
Two asteroids that have captured the world's attention in recent years—Bennu and Ryugu—may be siblings born from the violent collision of a much larger space rock billions of years ago. New observations from the James Webb Space Telescope suggest that both asteroids are fragments of a single massive parent body, a discovery that could reshape our understanding of how asteroid families form and scatter across the solar system.
Bennu, a roughly 500-meter-wide asteroid, was visited by NASA's OSIRIS-REx spacecraft in 2022, which collected samples and returned them to Earth in September 2023. Ryugu, slightly larger at around 900 meters across, was explored by Japan's Hayabusa2 probe in 2019, with samples arriving on our planet in December 2020. Both asteroids spin like tops and are classified as potentially hazardous due to their size and proximity to Earth, though neither poses a meaningful threat for at least the next century. NASA does monitor Bennu closely because of a small possibility it could approach Earth in 2182.
The leading theory about their origins points to the Polana asteroid family, created when a massive asteroid shattered in the early solar system. The largest surviving piece of this ancient collision is 142 Polana itself, a giant rock spanning more than 55 kilometers across, orbiting in the main asteroid belt between Mars and Jupiter. In a study published in The Planetary Science Journal on August 18, researchers led by Anicia Arredondo of Southwest Research Institute compared spectroscopy data from 142 Polana—collected by JWST—with physical samples of Bennu and Ryugu brought back by the spacecraft missions. The comparison revealed striking similarities in composition across all three asteroids, suggesting a common origin.
All three space rocks share the same fundamental makeup: carbon and magnetite, a rare form of iron oxide, appear in each. Yet the concentrations of these elements vary slightly between 142 Polana and the two smaller asteroids. Rather than contradicting the shared-parent theory, researchers believe these differences tell a story of time and exposure. Bennu and Ryugu now orbit much closer to the sun than Polana does, meaning their surfaces have been more heavily altered by solar radiation and solar particles. Meanwhile, 142 Polana is likely older and has endured billions of years of micrometeoroid impacts, which would have gradually changed its surface composition as well.
Arredondo explained the working hypothesis: in the solar system's infancy, large asteroids collided and fragmented into what became known as an asteroid family, with Polana as the largest remaining body. The new findings suggest that the same collision that created Polana also produced Bennu and Ryugu. "They are similar enough that we feel confident that all three asteroids could have come from the same parent body," Arredondo said. The evidence is compelling but not yet definitive—the subtle compositional differences mean researchers cannot yet claim absolute certainty. Still, a shared parent asteroid remains the best explanation for why these three distant rocks bear such a striking chemical resemblance to one another, and why their stories are now being read together across billions of kilometers of space.
Notable Quotes
Very early in the formation of the solar system, large asteroids collided and broke into pieces to form an asteroid family with Polana as the largest remaining body. The findings suggest that remnants of that collision created not only Polana, but also Bennu and Ryugu.— Anicia Arredondo, Southwest Research Institute
Bennu and Ryugu are now much closer to the sun than Polana, so their surfaces may be more affected by solar radiation. Polana is possibly older and would have been exposed to micrometeoroid impacts for a longer period, which could change aspects of its surface composition.— Tracy Becker, Southwest Research Institute
The Hearth Conversation Another angle on the story
Why does it matter whether these asteroids came from the same parent rock?
Because it tells us how the solar system was organized and reorganized in its earliest days. If we can trace asteroid families back to their origins, we understand the collisions that shaped our neighborhood.
But we already knew asteroids collide. What's new here?
The new part is having actual material in hand. We can hold Bennu and Ryugu samples in a lab and compare them directly to what JWST sees in 142 Polana. That's the difference between theory and proof.
The composition is slightly different though. Doesn't that undermine the connection?
Not really. It actually strengthens it. The differences make sense—one asteroid is closer to the sun, one is older, both have been weathered differently. The similarities are what matter.
So these asteroids are like geological siblings separated at birth?
Exactly. Separated about 4.5 billion years ago, scattered across the solar system, and now we're finally recognizing each other through chemistry.
What happens next? Do we need to study them more?
We'll keep watching them, especially Bennu. And we'll look for other asteroids that might belong to the same family. The more pieces we find, the clearer the picture of that original collision becomes.