Stop littering in space!

Britain recently began a diplomatic campaign to draw up new rules for responsible behaviour in space; essentially it's a "don't litter" policy intended to reduce the threat posed by decades of irresponsible dumping in orbit. But what’s the scale of the problem of space littering, and how might things go wrong? Adam Murphy spoke to John Zarnecki, emeritus professor of Space Sciences at the Open University and former president of the Royal Astronomical Society, starting with how much detritus we’ve left floating around up there already…