If you ever pictured yourself standing boldly on the surface of an asteroid, like Bruce Willis in Armageddon, maybe think again. Asteroids have very little gravity for a start and if you picked one like Bennu, you’d sink just like in a ball pit. NASA’s OSIRIS-REx sample collection didn’t encounter a solid surface but a loose collection of debris, according to new research.
NASA’s OSIRIS-Rex studied this celestial body for 505 days and even flew down to its surface to collect a sample. But the collection went a bit too well. It appears that its collecting arm penetrated about half a meter (1.5 feet) into the asteroid within seconds of touching down.
"It turns out that the particles making up Bennu's exterior are so loosely packed and lightly bound to each other that they act more like a fluid than a solid," UArizona Regents Professor of Planetary Sciences Dante Lauretta, the mission's principal investigator, said in a statement.
Lauretta is the lead author of a paper describing the unusual consistency of the surface of Bennu published in Science. A second paper, published in Science Advances, was lead by Kevin Walsh, a member of the OSIRIS-REx science team with Southwest Research Institute in Boulder.
The spacecraft risked being swallowed whole by the asteroid as it collected the sample. As OSIRIS-REx touched the ground in October 2020, pebbles began flying about. The timely ignition of its thruster kept it safe and led to the creation of a puzzling large crater 8 meters (26 feet) across.
"By the time we fired our thrusters to leave the surface we were still plunging into the asteroid," said Ron Ballouz, a former postdoctoral researcher at UArizona’s Lunar and Planetary Laboratory who is now based at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
Images taken during and after the sample collection descent, together with hundreds of simulations, revealed that Bennu is a lot less solid than previously expected. And this finding might have important consequences for planetary defense strategies.
Bennu is a Near-Earth Object that might impact Earth next century. Given how loose it is, the effect of the atmosphere would be different compared to a more solid asteroid.
OSIRIS-REx will deliver its precious sample to Earth next September and will then continue towards another dangerous object, asteroid Apophis, which it will reach in 2029.