For every potentially damaging asteroid spotted, there are millions falling towards the Earth unseen.
NASA's DART spacecraft successfully slammed into a distant asteroid at hypersonic speed on Monday.
A livestream showed images taken by DART's camera as the cube-shaped 'impactor' vehicle, streaked into the asteroid Dimorphos, about the size of a football stadium.
A car-sized asteroid flew past our planet over the last weekend, in the closest flyby of such space rocks on record. Scientists hardly had any information about it until it departed.
Asteroid 1998 OR2 was discovered by the Near-Earth Asteroid Tracking program at NASA's Jet Propulsion Laboratory in July 1998, and for the past two decades astronomers have tracked it.
While Bennu itself is too small to have ever hosted liquid water, the finding indicates that liquid water was present at some time on Bennu's parent body, a much larger asteroid.
Scientists estimate there is a one-in-2,700 chance of the asteroid slamming catastrophically into Earth 166 years from now.
The round, cookie tin-shaped robots successfully reached the Ryugu asteroid a day after they were released from the Hayabusa2 probe.