In a case of life imitating art, a 100-metre-wide asteroid has triggered global planetary defence procedures for the first time, after telescope observations revealed it had a chance of colliding with Earth in 2032. To find out what happens now and how worried we should be, Ian Sample hears from Richard Binzel, a professor of planetary sciences at MIT and inventor of the Torino scale, which is used to categorise the threat posed by objects such as asteroids and comets
