Key points from article :
100-metre wide space rock slipped through Nasa’s detection systems.
Asteroid "2019 OK" passed by a fifth of the distance to the moon.
Largest asteroid to pass so close to earth in the last century.
Direct hit would have created a blast wave causing localised devastation to an area roughly 50 miles across.
Brazilian observatory spotted it on 24 July just hours before its close encounter with Earth.
Originally seen on 7 July, but it was moving too slowly to be identified as a near-Earth object.
How many times this situation has happened without the asteroid being discovered at all?