n 2019, when NASA’s OSIRIS-REx spacecraft approached the asteroid Bennu, scientists saw something stunning in the images beamed back to Earth. The surface of the space rock wasn’t calm — instead, swarms of marble-sized rocks were popcorning off the asteroid.

Now, a new study of a meteorite that landed on Earth reveals how this asteroid activity occurs. Small collisions can dislodge the pebbles, which shoot off the asteroid but fall back, drawn in by the space rock’s gravitational pull. Another collision can then smush the loose pebbles back together, creating a kind of cement of minerals from all around the asteroid’s surface.

“It provides a new way of explaining the way that minerals on the surfaces of asteroids get mixed,” Xin Yang, a graduate student at the Chicago Field Museum and the University of Chicago and the first author of the new study, said in a statement.

Meteorite mystery

Previously, astronomers thought that asteroids had to undergo dramatic, high-speed, high-pressure collisions to reshape their surfaces, Philipp Heck, the curator of meteoritics at the Field Museum and the study’s senior author, said in the statement.

However, the new study, published Aug. 11 in the journal Nature Astronomy (opens in new tab), indicates that it actually doesn’t take much to morph an asteroid. The researchers discovered this when they examined a bit of the Aguas Zarcas meteorite, which fell in Costa Rica in 2019. Fragments of the space rock, which acquired a smooth glassy sheen as a result of the heating it experienced in the atmosphere, hit the roof of a house and a nearby doghouse, according to Arizona State University’s Buseck Center for Meteorite Studies.