NASA scientists were not expecting a dark, cold asteroid to be geologically active.
But in January 2019, while looking at photos of the asteroid, an OSIRIS-REx mission scientist noticed bright dots next to the asteroid Bennu that were definitely not background stars.
Those dots turned out to be small pieces of rock, seemingly shooting from the 800-foot asteroid.
Since the OSIRIS-REx spacecraft arrived at Bennu at the end of 2018, scientists have detected more than 300 events of particles shooting out of the asteroid and counted more than 600 individual particles.
These tiny rocks range in size from a quarter of an inch to two inches wide.
Now scientists have a couple of ideas about what’s causing these “particle ejection events.”
Because Bennu is so small (relatively) and has no atmosphere, it absorbs and releases a large amount of heat from the Sun every 4.3 hours as it turns on its axis. That repetition of absorbing and releasing heat stresses Bennu’s rocks.
The stress on the rocks can cause them to break, releasing debris as small rock particles.
Another theory is that tiny meteoroids are hitting Bennu on a regular basis, and those impacts send debris into space.
As the OSIRIS-REx team prepares to take a sample of the asteroid in October, scientists are doing everything they can to solve Bennu’s mysteries.