Deep Impact probe. Image 1 of 3. Illustration of the Deep Impact space probe firing an impactor to- wards the nucleus of comet Tempel 1 (lower left). The 500 kilogram impactor, travelling at 10 kilometres per second, will blast a large crater in the comet and eject material into space. Sens- ors on the space probe will monitor the explosion. The material inside the comet will be unchanged since the beginning of the solar system 5 billion years ago. This will provide information about the solar system's history. This NASA mission is due for launch in January 2004. For a sequence showing the impact, see images R250/139-141.