Deep Impact comet strike. Illustration of the Deep Impact space probe (lower left) as its impactor hits the nucleus of comet Tempel 1 (centre). This NASA mission was launched in January 2005. The impactor was released on 3 July 2005, and hit the comet around a day later on 4 July 2005. The 500 kilogram impactor, travelling at 10 kilometres per second, blasted a large crater in the comet and ejected material into space. Sensors on the space probe monitored the explosion to discover the composition of the comet, which consists of material from the beginning of the solar system some 5 billion years ago. The comet material was found to contain more rock, and less ice, than expected.