NASA admits 1000s of 'city killer' asteroids still haven't been found
Tens of thousands of undetected near-Earth asteroids at least 140 metres wide remain, and Earth currently lacks a ready spacecraft capability to actively deflect them.
Scientists Say Heck, Just Nuke a Killer Asteroid Heading for Earth
Nuclear detonations are more likely to deflect large asteroids than to pulverize them because asteroid materials are surprisingly resilient under extreme stress.