"The search for dangerous asteroids is about to begin in earnest:

Source: "Astronomy: Watching and waiting," The Economist, December 4th 2008.

The risk:

100 years ago. In 1908 an object about 50 metres (150 feet) across entered the atmosphere above Siberia. When it blew up it flattened some 2,000 square kilometres (800 square miles) of forest.

Experts in the field put the chances of a 1908-style event happening some time this century at about one in ten. That would be devastating if it occurred over a densely populated area—of which there are many more than there were a century ago.

The response:

On December 6th the University of Hawaii will activate a telescope designed specifically to look for dangerous asteroids. It is called PS1, a contraction of Panoramic Survey Telescope & Rapid Response System, and it is the first of four such instruments that will be used to catalogue as many as possible of the 100,000 or so near-Earth asteroids that measure between 140 metres and a kilometre across.

See also my earlier posting on the need to institutionalize a global system for managing this risk.