Plot synopsis: Comets pose one of the greatest threats to life on Earth - a threat that can only be countered if we find out more about them. In 2005, in an audacious bid to do just that, NASA scientists launched a space probe to collide with a comet in the emptiness of deep space. This film follows the amazing story of mission Deep Impact, from its inception through to the final nail-biting moments when the probe and comet Tempel 1 met head-on.