New Polana Collisional Family The primary asteroid belt in our solar system is the source of insights about nearby asteroids (101955) Bennu and (162173) Ryugu, which are the focus of NASA’s Osiris Rex missions. Currently, astronomers utilizing the NASA/ESA/CSA James Webb Space Telescope are gathering spectroscopic data from the family progenitor, (142) Polana, and comparing it to laboratory data from both spacecraft and near-Earth asteroids, revealing near-infrared spectral similarities that lend support to the hypothesis that they originated from the same protoplanetary body.
This image of this asteroid was captured on June 26, 2018 by Jaxa’s Hayabusa-2 Spacecraft optical navigation camera – telescopic (ONC-T). Image credits: Jakusa / University of Tokyo / Kochi University / Ricchiho University / Nagoya University / Chiba University of Technology / Nishimura University / Aizu University / AIST.
“We hypothesize that in the early formation of our solar system, a significant asteroid collided and broke apart, creating the Polana and the ‘Asteroid Family,’ the largest remaining body,” stated Dr. Anisia Aredondo, a researcher at the Southwest Research Institute.
“This theory posits that the remnants of that collision led to the formation of not just Polana, but also Bennu and Ryugu.”
“To validate this theory, we began analyzing the spectra of all three entities and comparing them.”
The researchers used time on Webb to observe Polana with two different spectral instruments targeting near-infrared and mid-infrared wavelengths.
The data was then contrasted with spectral information from physical samples of Ryugu and Bennu collected by two distinct space missions.
“Bennu and Ryugu are categorized as near-Earth asteroids as they orbit the Sun within Mars’ orbit,” they noted.
“However, they pose no threat to our planet, with closest approaches of approximately 3 million km (1.9 million miles) and 1.6 million km (1 million miles), respectively.”
“Bennu and Ryugu are relatively small compared to Polana; Bennu measures about 500 m in diameter (0.3 miles), while Ryugu is twice as large, but both Polana and Ryugu measure about 55.3 km (34.4 miles) wide.”
“Scientists believe that Jupiter’s gravity caused Bennu and Ryugu to drift out of their orbit near Polana.”
“Given their similarities, I am confident all three asteroids share a common parent,” she added.
This mosaic image of the asteroid Bennu consists of 12 images collected on December 2, 2018 by a 15-mile (24 km) Polycam instrument at Osiris-Rex. Image credit: NASA/NASA’s Goddard Space Flight Center/University of Arizona.
The authors indicate that while spectral data from the asteroids exhibit variations and discrepancies, they do not sufficiently invalidate the hypothesis that they all have a shared origin.
“Polana, Bennu, and Ryugu have been traversing their respective paths through our solar system since the collision that may have formed them,” remarks Dr. Tracy Becker from the Southwest Research Institute.
“Bennu and Ryugu are now much closer to the Sun compared to Polana, resulting in their surfaces being more influenced by solar radiation and solar particles.”
“Additionally, Polana is likely older than Bennu and Ryugu, and as such, has been subjected to impact from micrometeorites over an extended period.”
“This could potentially alter the surface areas containing their elemental compositions.”
A study detailing the survey results has been published in the Journal of Planetary Science.
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Anisia Aredondo et al. 2025. Planet. Sci. J. 6, 195; doi:10.3847/psj/ade395
Source: www.sci.news
