Asteroids Bennu and Ryugu are Part of Polana Collisional Family, Webb Observations Suggest

The new Polana collision family in the main asteroid belt of the solar system is the hypothetical origin of the asteroids of the near Earth (101955) Bennu, which was the target of the Osiris-Rex mission of NASA, and (162173) Ryugu, which was the target of the Hayabusa-2 mission in Jaxa. Now, astronomers using the NASA / ESA / CSA James Webb space telescope have obtained spectroscopic data from the family’s parent body, (142) Polana, and compared them with spaces and laboratory data of almost land asteroids, discovering the same similarities in their almost infrared spectra to support the theory that comes from the same asteroid parent.

This image of the Ryugu asteroid was captured by the Optical-Telescopic (ONC-T) navigation camera on the Jaxa Hayabusa-2 spacecraft on June 26, 2018, at a distance of 13.7 miles (22 km). Image credit: Jaxa / University of Tokyo / Kochi University / Rikkyo University / Nagoya University / Chiba Institute of Technology / Meiji University / Aizu University / Aist.

“Very early in the formation of the solar system, we believe that large asteroids collided and burst into pieces to form an asteroid family ” with Polana as the greatest body remaining,” said Dr. Anicia Arredondo, researcher at the Southwest Research Institute.

“The theories suggest that the remains of this collision have not only created Polana, but also Bennu and Ryugu.”

“To test this theory, we started looking at the spectra of the three bodies and comparing them to each other.”

The authors asked for time on webb to observe Poana using two different spectral instruments focusing on the almost infrared and infrared wavelengths.

They then compared that the data with the spectral data of physical samples from Ryugu and Bennu collected by two different spatial missions.

“Bennu and Ryugu are considered asteroids close to the earth because they orbit the sun in the orbit of March,” they said.

“However, they are not considered a danger to the land, having an approach closest to around 3 million kilometers (1.9 million miles) and 1.6 million km (1 million miles), respectively.”

“Bennu and Ryugu are relatively small compared to Polana. Bennu measures around 500 m (0.3 mile) in diameter, the size of the Empire State Building.”

“Ryugu is twice as large, but Polana both eclips them, measuring approximately 55.3 km (34.4 miles) wide.”

“Scientists believe that Jupiter’s gravity has pushed Bennu and Ryugu out of their orbit near Polara.”

“They are similar enough for us to convince ourselves that the three asteroids could have come from the same parent body.”

This mosaic image of Bennu asteroids is made up of 12 images collected on December 2, 2018 by the polycam instrument of Osiris-Rex from a range of 15 miles (24 km). Image credit: NASA / NASA’s Goddard Space Flight Center / University of Arizona.

The authors noted that the spectral data of asteroids had variances and differences, but not enough to refute the hypothesis that they all share a common origin.

“Polana, Bennu and Ryugu have all made their own trips through our solar system since the impact that could have formed them,” said Dr. Tracy Becker, also the Southwest Research Institute.

“Bennu and Ryugu are now much closer to the sun than Polana, so that their surfaces can be more affected by solar radiation and solar particles.”

“Likewise, Polana is perhaps older than Bennu and Ryugu and would therefore have been exposed to micro-meteoroid impacts for a longer period.”

“This could also change the aspects of its surface, including its composition.”

An article on results was published in the Journal of planetary sciences.

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Anicia Arredondo and al. 2025. JWST spectroscopy of (142) Polana: Connection with Neas (101955) Bennu and (162173) Ryugu. Planet. SCI. J 6, 195; Doi: 10.3847 / PSJ / ADE395