NASA says Bennu surprises include particle plumes and rough terrain

Asteroid Bennu, the space rock currently orbited by NASA's OSIRIS-REx spacecraft, has offered up a couple surprise discoveries over past weeks, according to the space agency. OSIRIS-REx arrived at Bennu back in December 2018, kicking off a couple years of observations before the spacecraft's eventual return to Earth. If everything goes as planned, NASA will receive a physical sample collected from Bennu.

Bennu is full of surprises, NASA said in a recent statement. Among the unexpected discoveries were particle plumes, and OSIRIS-REx now has the distinction of having made the first close-up observations of these plumes erupting from the surface of an asteroid. The mission's principal investigator Dante Lauretta explained:

The discovery of plumes is one of the biggest surprises of my scientific career. And the rugged terrain went against all of our predictions. Bennu is already surprising us, and our exciting journey there is just getting started.

The particle plumes were discovered on January 6, only days after the spacecraft arrived at Bennu. According to NASA, the asteroid has also revealed other surprises, not the least of which is how rugged it is. The space rock has much more — and quite larger — boulders than NASA had expected, forcing the team to adjust its planned sample collection mission.

Experts had expected Bennu's surface to be relatively smooth and even, but instead it is described as rough and densely covered in boulders. Scientists are evaluating the asteroid in search of a suitable landing site for the spacecraft's sample collection mission, but one hasn't been identified at this time.