When things get too close for comfort

On 15 February 2013, an asteroid 17 metres in size and weighing some 10,000 tons entered Earth’s atmosphere at around 64,000 kilometres per hour, exploding over Chelyabinsk in Russia. The energy released was equivalent to 500 kilotons of TNT, about 30 times that of the Hiroshima atomic bomb. The resulting blast wave damaged buildings and caused injuries to around 1200 people through flying debris and glass splinters. On the very same day, asteroid 2012 DA14, 45 metres in diameter, passed only 28,000 kilometres from Earth, beneath the orbits of TV and communications satellites. Despite the dramatic combination of the two unrelated events, the collision of a large asteroid or comet with Earth is actually a very rare event. But if such an impact were to occur it could trigger the worst natural catastrophe our civilisation has ever experienced. It is worth repeating to be absolutely clear: what we are talking about here is a minuscule risk, but one linked to potentially devastating consequences. Ignoring this risk is socially, politically and also economically very dangerous; it is a subject in which global thinking and acting is vital.