The World Today
MADRID, 18 (EUROPA PRESS)
New evidence supports that Bennu and Ryugu were originally part of the Polana asteroid family, in the main asteroid belt, between the orbits of Mars and Jupiter.
The study compared spectroscopic data from Polana with spacecraft and laboratory data from samples brought back from Bennu and Ryugu, discovering similarities in their near-infrared spectra sufficient to support the theory that they originated from the same asteroid.
“Very early in the formation of the solar system, we think large asteroids collided and broke up to form an ‘asteroid family,’ with Polana being the largest remnant (55 kilometers across),” said Dr. Anicia Arredondo of SwRI (Southwest Research Institute), lead author of the study, in a statement. “Theories suggest that the debris from that collision created not only Polana, but also Bennu and Ryugu. To test this theory, we began analyzing the spectra of the three bodies and comparing them with each other.”
Arredondo and his team requested time on the James Webb Space Telescope to observe Polana using two different spectral instruments focused on near- and mid-infrared wavelengths. They then compared those data with spectral data from physical samples of Ryugu and Bennu collected by two separate space missions.
The Japan Aerospace Exploration Agency's Hayabusa2 probe encountered Ryugu in 2018 and collected samples that were returned to Earth in late 2020. NASA's OSIRIS-REx probe encountered Bennu in 2020 and collected samples that were returned to Earth in late 2023.
Bennu and Ryugu are considered near-Earth asteroids because they orbit the Sun within the orbit of Mars; however, they are not considered a hazard to Earth, with closest approaches of approximately 3 and 1 million kilometers, respectively. Both Bennu and Ryugu are relatively small compared to Polana. Bennu has a diameter of approximately 0.6 kilometers, about the size of the Empire State Building. Ryugu is twice as large, but Polana dwarfs both of them, at approximately 53 kilometers across. Scientists believe that Jupiter's gravity pushed Bennu and Ryugu out of their orbit near Polana.
"They are similar enough to be confident that all three asteroids could come from the same body," Arredondo said.
The team observed that the asteroids' spectral data showed variations 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 journeys through our solar system since the impact that may have formed them,” said SwRI’s Dr. Tracy Becker, a co-author on the paper. Bennu and Ryugu are now much closer to the Sun than Polana, so their surfaces could be more affected by solar radiation and solar particles.
Polana is also likely older than Bennu and Ryugu and would therefore have been exposed to micrometeoroid impacts for a longer period, Becker added. This could also change aspects of its surface, including its composition.
