The near-Earth asteroid has a surface similar to a plastic bullet pit

“At the time we fired our thrusters to leave the surface, we were still plunging into the asteroid,” said Ron Ballouz, an OSIRIS-REx scientist based at Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, in a statement. Ballouz co-authored a pair of July studies published in the journals Science and Science Advances on the discovery.

“If Bennu was completely packed, it would imply almost solid rock, but we found a lot of empty space on the surface,” said study co-author Kevin Walsh, a member of the OSIRIS-Scientific team. REx from the Southwest Research Institute in Boulder, Colorado. , in a report.

So what would have happened if the spacecraft’s thrusters hadn’t fired right away?

“OSIRIS-REx may have sunk deeper inside the asteroid, which is both fascinating and frightening,” said study co-author Patrick Michel, a scientist at OSIRIS-REx and research director at the National Center for Scientific Research of the Côte d’Azur. ‘Observatoire d’Azur in Nice, France.

Bennu defies expectations

When the spacecraft arrived at Bennu in December 2018, the OSIRIS-Rex team was surprised to find that the surface of the asteroid was covered in rocks. Previous sightings had prepared them for sandy beach-like terrain.

Scientists also saw particles from the asteroid release into space.

“Our expectations for the asteroid’s surface were completely wrong,” study author Dante Lauretta, principal investigator of OSIRIS-REx at the University of Arizona, Tucson, said in a statement.

The spacecraft captured images of the site where it collected a Bennu sample, which further baffled the team. Although OSIRIS-REx tapped the asteroid very gently, it kicked up a massive amount of rocky debris and left a crater 26 feet (8 meters) wide.

“What we saw was a huge wall of debris radiating from the sample site,” said Lauretta, regent professor of planetary sciences and cosmochemistry at the University of Arizona’s Lunar and Planetary Laboratory. “We were like, ‘Holy cow!’ Whenever we tested the sample collection procedure in the lab, we barely did a divot.”

Before and after photos from the touchdown site show the dramatic difference. The footage reveals what looks like a depression on the surface, with several large boulders at its base. The sampling event itself likely caused this sunken landform. The asteroid’s dark surface also has more reflective dust near the collection point, showing where rocks were moved during the event. These changes are evident in the slider below.

When analyzing the spacecraft’s acceleration data, the team determined that it encountered very little resistance, about the same amount someone might feel when pushing the plunger of a French press. .

Knowing more about Bennu’s composition can help scientists study other asteroids, whether the goal is to plan missions like OSIRIS-REx or to protect Earth from potential collisions with space rocks.

An asteroid like Bennu, which barely holds together, could smash through Earth’s atmosphere, which could pose other risks even if it’s not a direct hit.

“We have to continue to physically interact with these bodies because that’s the only way to really determine their mechanical properties and their response to external actions,” Michel said. “Images are crucial but don’t give us the answer of whether they are weak or strong.”

OSIRIS-REx – which stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer – was NASA’s first mission sent to a near-Earth asteroid, and once there it performed the orbit the closest to a planetary body by a spacecraft to date. Bennu is the smallest object ever orbited by a spacecraft.

The memory of Bennu’s spacecraft is the largest sample collected by a NASA mission since moon rocks were brought back by Apollo astronauts.

Once OSIRIS-REx approaches Earth in 2023, it will jettison the capsule containing the sample, which will pass through Earth’s atmosphere and parachute into the Utah desert.

If OSIRIS-REx is still healthy after depositing the sample, then it will begin a new expedition to study other asteroids.