488-20 years

It has been 20 years since the world woke up to the news that a half mile diameter asteroid, 1997 XF11, discovered by Space Watch on Kitt Peak, had a slight chance of impacting the Earth in 2028. The NASA and JPL's Center for Near Earth Object Studies or CNEOS (see-neos) for short maps space rocks orbits, predicts when they will come close to us, and reliably determines each one's chance of impacting Earth.