On 4 July 2005 a 350-kg copper ‘bullet’, release from NASA’s Deep Impact spacecraft, slammed into the surface of comet Tempel 1 at a velocity of 10.3 km/s. The impact, which was the equivalent of 4.7 tonnes of TNT, created an enormous ejecta plume and a crater on the comet around 100 m wide and 30 m deep.