Video: Asteroid alert

Are we ready for it? (Image: Don Davis/NASA) The LSST telescope will sweep the entire sky in just three nights (Image: LSST Corporation)

See the world’s most spectacular impact craters

IT LOOKS inconsequential enough, the faint little spot moving leisurely across the sky. The mountain-top telescope that just detected it is taking it very seriously, though. It is an asteroid, one never seen before. Rapid-survey telescopes discover thousands of asteroids every year, but there’s something very particular about this one. The telescope’s software decides to wake several human astronomers with a text message they hoped they would never receive. The asteroid is on a collision course with Earth. It is the size of a skyscraper and it’s big enough to raze a city to the ground. Oh, and it will be here in three days.

Far-fetched it might seem, but this scenario is all too plausible. Certainly it is realistic enough that the US air force recently brought together scientists, military officers and emergency-response officials for the first time to assess the nation’s ability to cope, should it come to pass.

They were asked to imagine how their respective organisations would respond to a mythical asteroid called Innoculatus striking the Earth after just three days’ warning. The asteroid consisted of two parts: a pile of rubble 270 metres across which was destined to splash down in the Atlantic Ocean off the west coast of Africa, and a 50-metre-wide rock heading, in true Hollywood style, directly for Washington DC.

The exercise, which took place in December 2008, exposed the chilling dangers asteroids pose. Not only is there no …