The Earth just experienced the equivalent of strolling down the street and minding your own business when suddenly a baseball whistles by your ear. That baseball was asteroid 2019 OK, a previously undetected rock that zoomed by a little close for comfort Thursday.
First thing to note is the asteroid didn't actually hit us. It passed by safely. The rock is estimated to be somewhere between 56 feet (17 meters) and 128 feet (39 meters) in diameter.
The All-Sky Automated Survey for SuperNovae (ASAS-SN) project run by Ohio State University scans the sky for interesting happenings. ASAS-SN tweeted a look at the asteroid's trajectory, which came within 0.19 lunar distance of Earth. Lunar distance is the moon's average distance to Earth. If you come within 1 lunar distance, you're cosmically fairly close to our planet.
It's quite delightful that this sneaky asteroid didn't meet Earth directly. ASAS-SN tweeted that an asteroid of this size "would make quite a mess if it did collide: ~1 km crater, several megatons TNT equivalent at impact."