Crash and Burn

The Earth is constantly bombarded by small fragments of space debris, but somewhere in the Solar System a sizeable asteroid or comet is probably on a collision course with Earth. We don't know where or when the impact will happen but it may prove catastrophic for life on Earth. In the first of two programmes on the subject, Patrick Moore is joined by Jonathan Tate and Lembit Opik to discuss where this threat comes from and assesses the chances of impact from a Potentially Hazardous Object.