Asteroid NASA’s OSIRIS-REx mission landed on had a surface like a ‘pit of plastic balls’

Bennu turned out nothing like scientists had expected.

Mike Brown / reuters

Nearly two years ago, NASA made history when its OSIRIS-REx spacecraft briefly “tagged” 101955 Bennu to collect a regolith sample from the surface of the asteroid. While the mission won’t return to Earth until late next year, NASA shared new information about the celestial body. In an update published this week (via Mashable), the agency revealed OSIRIS-REx would have sunk into Bennu had the spacecraft not immediately fired its thrusters after touching the asteroid's surface.

"It turns out that the particles making up Bennu’s exterior are so loosely packed and lightly bound to each other that if a person were to step onto Bennu they would feel very little resistance, as if stepping into a pit of plastic balls that are popular play areas for kids," NASA said.

That’s not what scientists thought they would find on Bennu. Observing the asteroid from Earth, the expectation was that its surface would be covered in smooth, sandy beach-like material. Bennu’s reaction to OSIRIS-REx’s touchdown also had scientists puzzled. After briefly interacting with the asteroid, the spacecraft left a 26-foot (8-meter) wide crater. In lab testing, the pickup procedure “barely made a divot.”

After analyzing data from the spacecraft, they found it encountered the same amount of resistance a person on Earth would feel while squeezing the plunger on a French press coffee carafe. “By the time we fired our thrusters to leave the surface, we were still plunging into the asteroid,” said Ron Ballouz, a scientist with the OSIRIS-REx team.

According to NASA, its findings on Bennu could help scientists better interpret remote observations of other asteroids. In turn, that could help the agency design future asteroid missions. “I think we’re still at the beginning of understanding what these bodies are, because they behave in very counterintuitive ways,” said OSIRIS-REx team member Patrick Michel.