Asteroid that passed near Earth has a surface similar to a bullet pit, study finds

Asteroid that passed near Earth has a surface similar to a bullet pit, study finds

A near-Earth asteroid called Bennu has proven to be full of surprises – the most recent of which is that it has a surface similar to a pool of plastic balls, according to NASA scientists.

The new revelation comes after the space agency successfully sampled the asteroid in October 2020.

During the historic collection event, the sampling head of the OSIRIS-REx spacecraft sank 0.5 meters into the asteroid’s surface.

Apparently Bennu’s exterior is made of loose particles that aren’t held together very tightly, based on what happened when the spacecraft took a sample.

Had the spacecraft not triggered its thruster to retreat after its rapid collection of dust and rocks, it could have sunk directly into the cosmic object.

“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 two studies published in July in the journals Science and Science Advances on the discovery.

Bennu is a spinning top-shaped debris pile asteroid made up of rocks held together by gravity. It is about a third of 500 meters wide.

“If Bennu were fully compacted, it would imply nearly solid rock, but we found a lot of empty space on the surface,” study co-author Kevin Walsh, OSIRIS-REx science team member at Southwest Research Institute in Boulder, Colorado, said in a statement.

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

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

Fortunately, the spacecraft and its precious sample return to Earth. The Bennu sample is expected to arrive in September 2023.

Bennu defies expectations

When the spacecraft arrived at Bennu in December 2018, the OSIRIS-Rex team was surprised to find that the asteroid’s surface was covered in rocks. Previous sightings have prepared them for sandy, seaside terrain.

Scientists also saw particles from the asteroid being launched 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 footage of where it collected a Bennu sample, which further confused the team. Although the OSIRIS-REx spacecraft struck the asteroid very gently, it kicked up a huge amount of rocky debris and left an eight-meter-wide crater.

“What we saw was a huge wall of debris radiating from the sample site,” said Lauretta, professor of planetary sciences and cosmochemistry at the University of Arizona’s Lunar and Planetary Laboratory.

“We were like, ‘Shit!’ Every time we tested the sample collection procedure in the lab, we got virtually no dirt.”


The before and after photos of the landing site show the difference. The footage reveals what appears to be a depression on the surface, with several large boulders at its base.

The sampling event itself likely caused this sunken relief.

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.

By analyzing the spacecraft’s acceleration data, the team determined that it encountered very little resistance, about the same amount someone would feel when pushing through a ball pit.

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

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

“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 they don’t tell us if they are weak or strong.”

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

The memory of the Bennu 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 launch the capsule containing the sample, which will soar through Earth’s atmosphere and parachute into the Utah desert.

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

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