The nascent Polana collisional family residing within the main asteroid belt of our Solar System is posited as the progenitor of near-Earth asteroids such as (101955) Bennu, the focus of NASA’s OSIRIS-REx endeavor, and (162173) Ryugu, which was investigated by JAXA’s Hayabusa-2 expedition. Contemporary analysis, leveraging spectroscopic data acquired by the NASA/ESA/CSA James Webb Space Telescope from the family’s parent body, (142) Polana, has illuminated compelling spectral congruities. When juxtaposed with spectroscopic information from both near-Earth asteroids and laboratory-derived data, these findings reveal a remarkable similarity in their near-infrared signatures, thereby substantiating the hypothesis that these celestial bodies share a common asteroidal genesis.
“It is our prevailing belief that during the incipient stages of the Solar System’s formation, substantial asteroid impacts resulted in fragmentation, thus propagating an ‘asteroid family’ with Polana emerging as the principal surviving entity,” commented Dr. Anicia Arredondo, a researcher affiliated with the Southwest Research Institute.
“Theoretical frameworks propose that the fragments originating from that cataclysmic event not only gave rise to Polana but also contributed to the formation of Bennu and Ryugu.”
“To rigorously investigate this proposition, our initial step involved scrutinizing the spectral characteristics of all three celestial bodies, followed by a comparative analysis.”
The research team secured observation time with the Webb telescope to examine Polana, utilizing two distinct spectral instruments attuned to the near-infrared and mid-infrared portions of the electromagnetic spectrum.
Subsequently, this acquired data was meticulously compared with the spectral signatures derived from physical samples of Ryugu and Bennu, which had been retrieved by two separate space missions.
“The designation of Bennu and Ryugu as near-Earth asteroids stems from their orbital paths around the Sun, which fall within the trajectory of Mars,” they elucidated.
“Nevertheless, they are not categorized as posing a threat to our planet, with their nearest approach trajectories calculated at approximately 3 million kilometers (1.9 million miles) and 1.6 million kilometers (1 million miles), respectively.”
“In terms of dimensions, both Bennu and Ryugu are comparatively diminutive when set against Polana. Bennu measures approximately 500 meters (0.3 miles) in diameter, a size comparable to that of the Empire State Building.”
“While Ryugu is twice the size of Bennu, Polana eclipses both in magnitude, spanning an impressive width of roughly 55.3 kilometers (34.4 miles).”
“It is theorized by scientists that the gravitational influence of Jupiter played a role in displacing Bennu and Ryugu from their trajectories in proximity to Polana.”
“The observed similarities are sufficiently pronounced to inspire a high degree of confidence in the premise that all three asteroids could have originated from a singular parent body.”
The authors acknowledged that discernible variations and discrepancies were present within the spectral data gathered from the asteroids; however, these differences were deemed insufficient to invalidate the hypothesis of a shared common origin.
“Since the impact event that presumably engendered them, Polana, Bennu, and Ryugu have each embarked on distinct trajectories through our solar system,” stated Dr. Tracy Becker, who also contributes to the Southwest Research Institute.
“Presently, Bennu and Ryugu maintain orbits considerably nearer to the Sun compared to Polana, a proximity that may have led to more pronounced surface alterations due to solar radiation and energetic particles.”
“Concurrently, Polana, potentially predating Bennu and Ryugu, would have been subjected to micrometeoroid impacts over an extended duration.”
“Such prolonged exposure could likewise induce modifications to its surface characteristics, including its elemental composition.”
A treatise detailing these investigative outcomes has been formally published in the esteemed Planetary Science Journal.
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Anicia Arredondo et al. 2025. JWST Spectroscopy of (142) Polana: Connection to NEAs (101955) Bennu and (162173) Ryugu. Planet. Sci. J 6, 195; doi: 10.3847/PSJ/ade395
