Three asteroids, separated by vast distances, still bear the mark of a common ancestor.
Billions of years before human memory, a colossal asteroid shattered in the young solar system, scattering its children across the void. Now, through the patient eye of the James Webb Space Telescope and the physical testimony of returned samples, scientists have found that two of those wandering fragments — Bennu and Ryugu — carry the same chemical signature as their largest surviving sibling, 142 Polana. It is a story of origin written in carbon and iron oxide, legible only after humanity learned to read the language of light and stone. In tracing this ancient lineage, we also sharpen our understanding of the rocks that still share our neighborhood — and occasionally, our future.
- JWST spectroscopy has revealed that Bennu, Ryugu, and the much larger 142 Polana share the same core composition of carbon and magnetite, pointing to a single catastrophic collision billions of years ago.
- The finding carries quiet urgency: Bennu holds a small but real statistical chance of striking Earth in 2182, making its origins more than a matter of academic curiosity.
- Subtle compositional differences between the three asteroids complicate the picture — solar radiation and micrometeoroid impacts have slowly rewritten each rock's surface over billions of years.
- Researchers from Southwest Research Institute stop short of absolute certainty, acknowledging the current data is compelling but not yet conclusive.
- The study, published in The Planetary Science Journal, positions asteroid family research as a foundation for future planetary defense strategies — knowledge that grows more urgent as tracking technology improves.
Billions of years ago, a massive asteroid was destroyed in a collision somewhere in the early solar system. Two of its fragments — Bennu and Ryugu — have been drifting through space ever since, and new data from the James Webb Space Telescope now suggests they share a common origin with 142 Polana, the largest surviving remnant of that ancient impact.
Researchers from Southwest Research Institute compared JWST spectroscopy of Polana with physical samples returned to Earth by NASA's OSIRIS-REx and Japan's Hayabusa2 missions. What they found was striking: all three asteroids share the same core composition — carbon and a rare form of iron oxide called magnetite. Lead author Anicia Arredondo concluded that a shared parent body offered the most coherent explanation, describing the collision as one of the solar system's formative events, with Polana as its largest surviving piece.
The three asteroids are not identical, however. Bennu and Ryugu orbit much closer to the sun than Polana, exposing them to stronger solar radiation and particle bombardment, which alters surface composition over time. Polana, older and farther out, has been shaped by billions of years of micrometeoroid impacts. Co-author Tracy Becker noted these environmental histories likely account for the subtle differences observed.
The study, published in The Planetary Science Journal on August 18, stops short of a definitive conclusion but points strongly toward a shared lineage. The stakes are not purely historical: Bennu carries a small collision risk with Earth in 2182, and understanding how asteroid families form and disperse could one day inform strategies for planetary defense.
Billions of years ago, a massive asteroid collided with something equally large in the early solar system. The impact shattered it into pieces. Two of those fragments—the asteroids Bennu and Ryugu—may have drifted through space ever since, carrying with them a chemical signature that now, thanks to the James Webb Space Telescope, reveals their shared origin.
New spectroscopy data collected by JWST and compared with samples brought back to Earth by two separate spacecraft suggests that Bennu and Ryugu are siblings, both born from the same parent body. That parent, researchers believe, was a colossal asteroid that fragmented in the solar system's infancy. The largest surviving piece of this ancient collision is 142 Polana, a rock spanning more than 34 miles across, still orbiting in the asteroid belt between Mars and Jupiter. The two smaller fragments—Bennu, roughly 1,650 feet wide, and Ryugu, about 2,950 feet across—have since wandered closer to the sun, where they became targets of human curiosity.
Bennu was visited by NASA's OSIRIS-REx spacecraft in 2022, which collected samples and returned them to Earth in September 2023. Ryugu received a visit from Japan's Hayabusa2 probe in 2019, with samples arriving on our planet in December 2020. Both asteroids are shaped like spinning tops and both are classified as potentially hazardous due to their size and proximity to Earth, though neither poses an immediate threat. Bennu does carry a small statistical risk—a collision possibility in 2182—which is why NASA continues to monitor it closely.
When researchers from Southwest Research Institute compared the spectroscopy data from 142 Polana with the actual material from Bennu and Ryugu, they found something striking: all three asteroids share the same core composition. Carbon and magnetite, a rare form of iron oxide, appear in all three. The resemblance was strong enough that Anicia Arredondo, the study's lead author, and her team concluded that a shared parent asteroid offered the best explanation for what they were seeing. "Very early in the formation of the solar system, we believe large asteroids collided and broke into pieces to form an 'asteroid family' with Polana as the largest remaining body," Arredondo said. The findings suggest that the same collision that created Polana also created Bennu and Ryugu.
But the picture is not entirely clean. The three asteroids show subtle differences in the concentrations of their shared elements. These discrepancies likely stem from what has happened to each rock since the breakup. Bennu and Ryugu now orbit much closer to the sun than Polana does, exposing their surfaces to more intense solar radiation and solar particles, which can alter composition over time. Polana, meanwhile, is likely older and has endured billions of years of micrometeoroid impacts, each one subtly changing its surface. Tracy Becker, a co-author on the study, noted that these environmental factors could explain why the asteroids are similar but not identical.
The research, published in The Planetary Science Journal on August 18, does not yet offer absolute certainty. The team acknowledges that a definitive conclusion cannot be reached with current data. But the evidence points strongly in one direction: three asteroids, separated by vast distances and billions of years of exposure to the solar system's harsh environment, still bear the unmistakable mark of a common ancestor. Understanding how asteroid families form and scatter throughout the solar system could eventually inform strategies for planetary defense—knowledge that becomes more valuable as we learn to track and potentially deflect objects that might one day threaten Earth.
Citas Notables
Very early in the formation of the solar system, we believe large asteroids collided and broke into pieces to form an 'asteroid family' with Polana as the largest remaining body.— Anicia Arredondo, planetary scientist at Southwest Research Institute
They are similar enough that we feel confident that all three asteroids could have come from the same parent body.— Anicia Arredondo
La Conversación del Hearth Otra perspectiva de la historia
So these two asteroids that we've actually touched—we sent robots to them—might be pieces of something much larger that broke apart?
Yes. The James Webb data suggests they're fragments of a parent asteroid that collided and shattered billions of years ago. The largest piece still exists, 142 Polana, and it's enormous—34 miles wide.
How do we know they're related? They're so far apart now.
Chemistry. All three asteroids share the same core composition—carbon, magnetite, the same elements in similar proportions. It's like finding three pieces of pottery with the same clay and glaze.
But if they're from the same parent, why aren't they identical?
Time and location. Bennu and Ryugu drifted closer to the sun, so solar radiation has weathered them differently. Polana stayed farther out but has been pummeled by micrometeorites for longer. Each has a different story written on its surface.
Does this matter for Earth?
It matters for understanding how asteroids move and scatter through the solar system. Bennu itself has a small chance of hitting us in 2182. The more we understand about asteroid families and their behavior, the better we can predict and defend against future threats.
So this isn't just ancient history.
No. It's a map of how the solar system works, written in rock.