Study reveals the asteroid’s sponge-like porous texture

When NASA’s OSIRIS-REx arrived at the asteroid Bennu in 2018, geologists were expecting to find it covered in a layer of smooth dust, known as regolith. Instead the mission found itself above a world of rocks and boulders. Now a new study suggests this rockiness could be down to the asteroid’s sponge-like, porous texture.

To investigate why Bennu has so little regolith, researchers studied infrared emissions from the surface. These showed where the regolith is but also how porous the rocks are, and it seems that the more spongy a rock is, the less likely it is to have dust around it. The investigators think that the porous rocks absorb the impacts of micrometeorites that would otherwise fragment into dust when they hit Bennu.

“Basically, a big part of the energy of the impact goes into crushing the pores, restricting the fragmentation of the rocks and the production of new fine regolith,” says Chrysa Avdellidou from the French National Centre for Scientific Research, who helped with the study. www.asteroidmission.org