Detecting and deflecting the asteroid threat

For the inhabitants of the Russian city of Chelyabinsk, the events of 15 February 2013 will never be forgotten.

Just after nine o’clock in the morning, as commuters made their way to work along the city’s snow-covered roads, and schoolchildren settled down for their lessons, a 20 metre diameter meteorite - travelling at an estimated 12 miles per second - exploded above the city with a force equivalent to 30 Hiroshima bombs.

Amazingly, no one was killed. But the resulting shockwave and shower of cosmic debris wreaked havoc over a wide area: damaging thousands of buildings, putting around 1600 people in hospital and drawing international attention to a risk that astronomers, scientists and Hollywood film-makers have been nervously contemplating for decades.

Every year, around 40,000 tonnes of space rock falls to the earth. This is mostly in the form of dust and small meteorites but occasionally something more substantial will enter our atmosphere. The Chelyabinsk meteor was thought to be the largest object of its kind since the so-called 1908 Tunguska event, when an asteroid of around 40m diameter devastated a 2000km2 area of remote Siberian forest.