In October 2020, a small spacecraft briefly touched down on an asteroid to take a piece to bring towards the earth. Nearly two years later, scientists learned that if the OSIRIS-REx spacecraft had extended its stay even a little longer, it would have sunk directly into the asteroid.
This is because the Bennu asteroid is nothing like what scientists predicted. Rather than being a solid, flying rock, Bennu is actually made up of small pebble-like particles that are not strongly bonded together, creating a lot of space on its surface. It’s more like a plastic ball pit, NASA writes in a new Release. “Our expectations of the asteroid’s surface were completely wrong” Dante Lauretta, principal investigator of OSIRIS-REx and lead author of a recent paper detail the findingssaid in the release.
OSIRIS-REx arrived on the asteroid in December 2018 with the mission of recovering a sample of Bennu and wear it on Earth for analysis. The spacecraft landed on Bennu in October 2020, extending its robotic arm to pick up a piece of the asteroid. OSIRIS-REx then immediately fired its thrusters to get away from Bennu. The spacecraft’s sampling head touched Bennu’s surface for about 6 seconds before withdrawing. By stirring up some of the dust and pebbles on the asteroid, OSIRIS-REx was able to grab a few ounces of material.
The brief encounter left a strong impression on Bennu, resulting in a chaotic explosion of pebbles and one crater 26 feet (8 meters) wide. “Whenever we tested the sample collection procedure in the lab, we barely did a divot,” Lauretta said. But after reviewing the images of the real collection of samples, the scientists remained perplexed. “What we saw was a massive wall of debris radiating from the sample site,” Lauretta said. “We were like, ‘Holy cow!'”
After analyzing the volume of debris seen before-and-after the pictures of landing site, scientists learned that OSIRIS-REx faced as much resistance landing on the asteroid as “a person would feel pressing the plunger on a French-press coffee carafe,” NASA wrote in a statement. That is, the spacecraft encountered very little resistance, certainly not the type of resistance one would expect when landing on a rocky body. As the spacecraft launched its thrusters to departit was sinking into the asteroid.
“If Bennu was completely packed, it would imply nearly solid rock, but we found a lot of empty space on the surface,” said OSIRIS-REx science team member Kevin Walsh. and lead author of a second paper on the composition of Bennu, said in a statement.
When OSIRIS-REx first arrived on the asteroid, close-up images of Bennu revealed that its surface was filled with boulders, rather than the smooth sand surface that had been predicted. The footage also showed Bennu spitting pebbles into space.. “I think we’re still at the beginning of understanding what these bodies are, because they behave in very counter-intuitive ways,” OSIRIS-REx scientist Patrick Michel said in the release. Nasa.
Bennu was filled with surprises. One of the first was its odd shape, similar to a for children spinning top.