Asteroid family link strengthened by SwRI analysis of Bennu and Ryugu
The team compared Polana spectroscopy data with spacecraft and laboratory results from Ryugu and Bennu, revealing strong similarities in their near-infrared spectra that support a shared parent body.
"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," explained SwRI's Dr. Anicia Arredondo, the study's lead author. "Theories suggest that remnants of that collision not only created Polana, but also Bennu and Ryugu as well. To test that theory, we started looking at spectra of all three bodies and comparing them to one another."
Arredondo and her colleagues secured James Webb Space Telescope time to capture near- and mid-infrared observations of Polana. They then compared those results with spectral data from physical samples. JAXA's Hayabusa2 mission collected and returned Ryugu material in 2020, while NASA's OSIRIS-REx spacecraft delivered Bennu samples to Earth in 2023.
Bennu and Ryugu orbit the Sun within Mars's path, making them near-Earth asteroids, but neither poses a danger. Bennu, roughly one third of a mile across, is about the size of the Empire State Building. Ryugu is about twice as large, while Polana measures approximately 33 miles in diameter. Researchers believe Jupiter's gravity nudged Bennu and Ryugu away from their original orbits near Polana.
"They are similar enough that we feel confident that all three asteroids could have come from the same parent body," Arredondo said.
Although spectral differences were noted, none were sufficient to rule out a common origin.
"Polana, Bennu and Ryugu have all had their own journeys through our solar system since the impact that may have formed them," added SwRI's Dr. Tracy Becker, a co-author. "Bennu and Ryugu are now much closer to the Sun than Polana, so their surfaces may be more affected by solar radiation and solar particles.
"Likewise, Polana is possibly older than Bennu and Ryugu and thus would have been exposed to micrometeoroid impacts for a longer period," Becker continued. "That could also change aspects of its surface, including its composition."
Research Report:JWST spectroscopy of (142) Polana: Connection to NEAs (101955) Bennu and (162173) Ryugu"
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