The OSIRIS-REx spacecraft and its PolyCam instrument collected 12 images to make this mosaic of asteroid Bennu on December 2, 2018. The spacecraft was just 15 miles (24 km) from the asteroid. Scientists were surprised to see Bennu’s surface strewn with boulders. Image via NASA/ University of Arizona.
Why does near-Earth asteroid Bennu have so many boulders on its surface? Prior to late 2018, when NASA’s visiting spacecraft OSIRIS-REx visited Bennu, scientists expected the asteroid to have a surface entirely or partly coated in a fine regolith of sand and pebbles. In fact, the REx in OSIRIS-REx stands for Regolith Explorer. But OSIRIS-REx found Bennu’s surface strewn with boulders and large rocks. This month (October 21, 2021), scientists announced they might now have an answer to asteroid Bennu’s boulder mystery.
The new study, published in the peer-reviewed journal Nature on October 6, 2021, comes from the University of Arizona. The study suggests that porous rocks are responsible for the lack of fine regolith on Bunnu’s surface.
Asteroid Bennu’s boulder mystery: rocks but no sand
Scientists had thought Bennu would be covered in fine regolith. Close-up images from a spacecraft showed it nearly completely covered in large boulders. How could that ...