NASA are sending a probe into the comet 9P/ Tempel-1, early on the morning of 4 July 2005. This is a unique event, from which they hope to find out how comets are made. Are they balls of ice and mud, the harbourers of life's components, or just solid rocks of sterile cosmic debris? The Deep Impact programme hopes to provide the answers, but this destructive act is not without its critics. The Sky at Night explores the pros and cons of hitting a comet.

The search for life elsewhere in our Universe has long been the Holy Grail for astronomers. Planets around distant stars have recently been discovered and we now realise that solar systems like our own could be widespread. So is life on Earth unique? With missions to Mars, Saturn's moon Titan and Jupiter's moon Europa, we could be nearing an answer. No definitive traces of life have been found elsewhere, but astronomers are probing ever deeper on our nearest planetary neighbours and across our Universe for the signitures of life. Patrick Moore discusses the issue with Professor Monica Gardy and Professor Simon Conway Morris.Chris Lintott spends a night meteor-watching with Dr John Mason, Martin Mobberly and Martin Andrews. Every year the Earth passes through dusty tail remnants of the comet Swift-Tuttle. These enter Earth's atmosphere-forming meteor showers called the perseids, this year they are at their maximum in mid-August.