After reviewing data received when NASA’s OSIRIS-REx mission recovered a sample of the asteroid Bennu in October 2020, scientists have discovered something astounding. After collecting a sample of dust and rock from Bennu’s surface, the spacecraft would have sunk into the asteroid if it hadn’t instantly fired its engines to back away.
Unexpectedly, it turns out that the particles comprising Bennu’s shell are so loosely packed and weakly bonded to one another that a person would feel very little resistance if they stepped upon the asteroid. It would be like going into a children’s playground filled with plastic balls.
Kevin Walsh, a member of the OSIRIS-REx research team from the Southwest Research Institute in San Antonio, stated, “If Bennu were entirely packed, it would indicate virtually solid rock, but we detected a great deal of empty space on the surface.”
The most recent discoveries regarding the surface of Bennu were published on July 7, 2022 in the journals Science and Science Advances by Dante Lauretta, the main investigator of OSIRIS-REx at the University of Arizona in Tucson, and Kevin Walsh. These unexpected findings add to the mystery that has captivated scientists during the OSIRIS-REx mission, since Bennu has constantly shown to be unpredictable.
Bennu offered its first surprise in December 2018, when a NASA probe landed at the asteroid. The OSIRIS-REx team discovered a rocky, boulder-strewn surface instead of the predicted sandy beach based on Earth- and space-based telescope measurements. Additionally, researchers determined that Bennu was ejecting rock fragments into space from its surface.
“Our assumptions regarding the surface of the asteroid were entirely off,” stated Lauretta.
The OSIRIS-REx expedition, which recovered a sample and relayed beautiful photos of Bennu’s surface to Earth, provided the most current evidence that the asteroid was not what it seemed to be. The sample location was surrounded by a huge wall of rubbish, as Lauretta put it. When we saw what had happened, we both exclaimed, “Holy cow!”
Astroid close to Earth Bennu is a pile of leftover rocks and boulders from the formation of the solar system. On October 20, 2020, the OSIRIS-REx spacecraft of NASA briefly landed on Bennu and gathered a sample for return to Earth. During this incident, the spacecraft’s arm penetrated the asteroid’s surface far deeper than anticipated, demonstrating that Bennu’s surface is weakly bonded. Now, scientists have utilized OSIRIS-REx data to revisit the sample-collection event and get a clearer understanding of how the loose top layers of Bennu are kept together.
Given how lightly the spacecraft touched the surface, mission scientists were perplexed by the abundance of strewn pebbles. Even stranger was the fact that the spaceship left a 26-foot-wide (8-meter-wide) crater. “Each time we tried the sample collection method in the laboratory, we hardly produced a divot,” Lauretta explained. Lauretta stated that the mission crew chose to send the spacecraft back to take further images of Bennu’s surface “to assess how much of a mess we caused.”
The volume of debris seen in before and after photographs of the “Nightingale” sample site was studied by researchers. In addition, they examined acceleration data gathered during the spacecraft’s touchdown. This data indicated that when OSIRIS-REx touched the asteroid, it encountered the same amount of resistance as when a human presses the plunger of a French press coffee carafe. “When we ignited our engines to leave the surface, we were already plummeting into the asteroid,” said Ron Ballouz.
Ballouz and the research team used numerous of computer simulations based on satellite images and velocity data to assess the density and cohesiveness of Bennu. Engineers altered the surface cohesion parameters of each simulation until they discovered the one that most closely matched their actual data.
Now, this detailed knowledge about Bennu’s surface will assist scientists in better interpreting remote observations of other asteroids, which may be valuable for designing future asteroid missions and creating measures to protect Earth from asteroid crashes.
Bennu-like asteroids, that are solely held together via gravity or electrical force, pose a different hazard than solid asteroids since they might potentially dissolve in Earth’s atmosphere. Patrick Michel, an OSIRIS-REx scientist, stated, “I think we’re just at the beginning of knowing what these entities are, since they act in really surprising ways.”