Nasa Cannot Monitor Most Potentially Devastating Asteroids

Asteroid 2012 DA14 will not hit Earth when it whizzes past us on Friday - but we may not be so lucky in future, space experts fear. Although the 150ft (45m) rock will zoom harmlessly by our planet on its record near approach this week, it is just one of up to a million "near-Earth objects" which astronomers believe could one day pose a serious threat.

A program set up by NASA to monitor so-called "NEOs" a decade and a half ago has so far tracked fewer than 10,000, meaning the vast majority are still hidden. Most of the larger specimens, which could have the potential to wipe out entire continents, have been found but even small asteroids like 2012 DA14 could be powerful enough to destroy an entire city if they plunged down to Earth.

Now experts are calling for greater monitoring of small NEOs measuring less than a kilometre across, and for a contingency plan in the event of a likely impact...