Should a massive asteroid be on a trajectory to impact the Earth, there wont necessarily be any warning.
DailyStar reports that asteroid 2017-VL2 zipped past the Earth on November 9th, and NASA didn’t even notice.
While the size of the asteroid seems unintimidating, measured 12-36 meters wide, a direct impact could have annihilated an area the size of New York city.
The space-rock came within 76,000 miles of Earth, a very near miss given the astronomical metrics used to measure space.
And NASA didnt see it coming.