Asteroids are the rubble left over from the formation of the solar system. A collision with Earth of a 1 km sized asteroid would cause severe damage. If the asteroid was 10 km in size, it would wipe out all life. There are potentially several hundred thousand such 'Near Earth Objects', or NEOs, in space, any one of which could be a potential collider. Scientists have suggested several methods man could use to deflect a NEO, given enough advance warning. Here are some of them.