NASA scientists have made what they describe as an “astonishing” discovery about Bennu, the asteroid from which its OSIRIS-REx spacecraft collected a sample of rock and dust in 2020.
The space agency said this week that it turns out that the particles that make up Bennu’s exterior are much more loosely bound than expected. In fact, if you walked on it, there would be virtually no resistance, “like stepping into a pit of plastic balls which are popular playgrounds for children”.
NASA revealed the discovery this week after analyzing data collected during the spacecraft’s brief landing on the asteroid two years ago.
As shown in the video below, the spacecraft touched down on the asteroid before causing an explosion to allow it to collect material. Nine seconds after making contact, the spacecraft fired its thrusters to push it back from the rock below, but NASA said if it hadn’t, it “would have sunk into Bennu.”
Scientists first realized that Bennu might have a loosely bonded surface when they noticed that the spacecraft’s relatively soft touch was flying a huge amount of debris. “Even more bizarre, the spacecraft left a large crater 26 feet (8 meters) wide,” NASA said.
The surprise results were published July 7 in the journals Science and Science Advances.
“These findings add to the intrigue that kept scientists on edge throughout the OSIRIS-REx mission, as Bennu proved to be consistently unpredictable,” NASA said.
Indeed, as the space agency notes, Bennu offered its first surprise when OSIRIS-REx arrived at the asteroid in 2018. Instead of finding a surface resembling a “smooth beach of sand”, what observations telescopes from Earth and space had suggested, the mission team discovered that it was “strewn with rocks”.
To determine the surface density of the asteroid, scientists analyzed spacecraft acceleration data and images captured during the landing process, then ran hundreds of computer simulations until all the data match.
NASA said the data could help it make more accurate remote observations of distant asteroids, which could allow it to make better predictions if one is heading our way.
Scientists believe, for example, that Bennu, which they say is “barely held together by gravity or electrostatic force”, could break up in Earth’s atmosphere and therefore present a different kind of danger than solid asteroids.
“I think we’re still at the beginning of understanding what these bodies are, because they behave in a very counter-intuitive way,” said OSIRIS-REx scientist Patrick Michel.
OSIRIS-REx is on its way back to Earth and is expected to deliver the sample from asteroid Bennu in September 2023.
Scientists believe that Bennu formed during the first 10 million years of our solar system’s existence. The sample could therefore tell more about its origin and perhaps unravel some of the mysteries about the origins of life.