But even if Spaceguard does succeed, another problem remains smaller asteroids, of the size believed to have caused a huge explosion above Tunguska, in Russia, in 1908.

ECONOMIST: A large asteroid sweeps by Earth. Where are the others?

Any NEO that is going to hit the Earth will swing near our planet many times before it hits, and it should be discovered by comprehensive sky searches like Spaceguard.

FORBES: We Probably Wouldn't Even See A Doomsday Asteroid Until It Was Too Late