Guess what? Astronomers have “eliminated most of the risk from global-scale, civilization-ending asteroid impact events during our lifetimes and the lifetimes of our grandchildren.”
They really ought to be bragging about this. But no. It was buried deep in the middle of an article in Sky & Telescope. The article was about the asteroid that hit the Russian city of Chelyabinsk this February. People wondered why astronomers didn’t detect the object before impact. Part of the answer is that it is relatively small, compared to the asteroids we really need to worry about. NASA began a program in 1992 called the Spaceguard Survey Report, with a goal of finding 90% of the objects that are near Earth and larger than 1 kilometer.
And . . . mission accomplished! Now they can look for the smaller stuff, the kind that has the ability to kill people but not wipe out entire civilizations.
(From “The Chelyabinsk Super-Meteor” by Daniel D. Durda in the June 2013 issue of Sky & Telescope.)