NASA Says This Asteroid Is Like A Chuck E Cheese Ball Pit For Spacecrafts

asteroid bennu
NASA's OSIRIS-REx spacecraft came upon an unsettling circumstance when it attempted to retrieve a sample from asteroid Bennu back in 2020. After analyzing data gathered by its instruments, the team was astonished to ascertain that the spacecraft would have sunk into Bennu had it not fired its thrusters to back away immediately.

The Origins Spectral Interpretation Resource Identification Security - Regolith Explorer (OSIRIS-REx) spacecraft first arrived at asteroid Bennu in 2018. The team found a surface littered with boulders, instead of the smooth, sandy beach they had anticipated based on observations from Earth and space-based telescopes. It was also found that the asteroid was "spitting particles of rock into space," according to NASA.

"Our expectations about the asteroid's surface were completely wrong," remarked Dante Lauretta, principal investigator of OSIRIS-REx.

It seems that Bennu was not done providing surprising results, as researchers have determined that the surface was not only different from what they expected in appearance, but in composition as well. New findings show that Bennu's exterior is so loosely packed and lightly bound to each other, that if someone were to step onto Bennu they would feel little to no resistance. NASA says it would be "as if stepping into a pit of plastic balls that are popular play areas for kids."

"If Bennu was completely packed, that would imply nearly solid rock, but we found a lot of void space in the surface," stated Kevin Walsh, a member of the OSIRIS-REx team.

The latest findings about Bennu's surface has been published in the journals Science and Science Advances on July 7, 2022. It includes when the spacecraft picked up a sample and beamed close-up images of the asteroid's surface back to Earth. "What we saw was a huge wall of debris radiating out from the sample site. We were like, 'Holy cow!'," exclaimed Lauretta.

Scientists were astonished by the shear amount of pebbles that were strewn about, in relation to how gently the spacecraft touched the surface. What was even more surprising to the team was how large of a crater the spacecraft left. The crater was 26 feet (8 meters) wide, according to NASA.

"Every time we tested the sample pickup procedure in the lab, we barely made a divot," stated Lauretta. It was then that the research team decided to send the spacecraft back to the asteroid to take more photographs of Bennu's surface "to see how big of a mess we made," added Lauretta.

Once the new photographs were obtained, mission scientists analyzed the volume of debris in before and after images of the sample site, named "Nightingale". The team also looked at the acceleration data collected during the spacecraft's touch down. That data revealed that as OSIRIS-REx touched the asteroid, it experienced the same resistance as "a person would feel while squeezing the plunger on a French press coffee carafe."

bennu asteroid
Image Credit: NASA

NASA indicated that the team ran hundreds of computer simulations to figure out Bennu's density and cohesion based on spacecraft images and acceleration data. During the simulations, engineers varied the surface cohesion properties in each simulation until the team found the one that most closely matched the real-life data.

One interesting piece of information deduced is the possibility that asteroids that are barely held together by gravity or electrostatic force, like Bennu, could essentially break apart in Earth's atmosphere and present an entirely different type of hazard than solid asteroids.

"I think we're still at the beginning of understanding what these bodies are, because they behave in very counterintuitive ways," said Patrick Michel, an OSIRIS-REx scientist.