Asteroid Bennu is made up of ‘quick pebbles’ that nearly engulfed a spacecraft

(ORDO NEWS) — In October 2020, a small spacecraft briefly landed on an asteroid to collect soil samples and bring them back to Earth.

Almost two years later, scientists learned that if the OSIRIS-REx spacecraft had extended its stay just a little bit longer, it could literally sink right into the asteroid.

This is because the Bennu asteroid is not at all what scientists predicted. Instead of being a hard piece of rock, Bennu is actually made up of small, pebble-like particles that are loosely bonded to each other.

It looks more like a children’s pool with plastic balls, according to NASA experts. “Our expectations for the surface of the asteroid were completely wrong,” said Dante Lauretta, OSIRIS-REx principal investigator and lead author of a recent paper detailing her findings.

OSIRIS-REx arrived at the asteroid in December 2018 on a mission to collect a sample from Bennu and bring it back to Earth for analysis. The spacecraft landed on Bennu in October 2020 and scooped up rock fragments with a robot arm.

The OSIRIS-REx then immediately started its engines and took off. The spacecraft’s sampling head touched Bennu’s surface for about 6 seconds, which was enough.

The short rendezvous made a strong impression on Bennu, and the result was a chaotic explosion of pebbles, after which a crater 8 meters wide was formed.

“Every time we tested the sampling procedure in the lab, we were just barely on time,” recalls Lauretta . But after reviewing the footage from taking a real sample, scientists were left in confusion. “What we saw was a huge wall of debris radiating from the sampling site. We yelled “Holy cow!”

After analyzing the amount of debris seen in the before and after images of the landing site, the scientists learned that the OSIRIS-REx encountered extremely little resistance when landing on the asteroid – no more than if you “pressed the French press plunger,” NASA writes.

In other words, this resistance is nowhere near what one would expect when landing on a solid rock body. By the time the spacecraft fired up its engines, it was actually already sinking into the asteroid.

When OSIRIS-REx first arrived at the asteroid, close-up images of Bennu showed that its surface was filled with boulders, not sand as expected. The photos also showed Bennu slowly spewing pebbles into space.

“I think we’re still at the beginning of understanding what these bodies are because they behave in a very counterintuitive way,” Patrick Michel, OSIRIS-REx scientist, explained in a NASA press release.


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