How to defend Earth from incoming asteroids

There are about a million near-Earth asteroids that are large enough to damage or destroy a major city, as evidenced by the explosion over Chelyabinsk, Russia, this past February of a meteor that injured more than 1,000 people. This month, Ukrainian astronomers detected a 1,350-foot-wide asteroid that made a close… » 10/18/13 5:06pm 10/18/13 5:06pm