I Geoff Watts presents the cutting-edge science programme. This week he looks at the biggest object ever placed in orbit - the Mir space station, and investigates what will happen when it falls to Earth later this month. When it does, its debris will rain down from the sky and scatter across an area the size of Siberia. The Russians are hoping to ensure that Mir's plunge will be a safe one, but the odds are against them - there is a chance of a fragment hitting a human being atjust over 100 to one. Producer Alexandra Feachem. E-MAIL: scirad@bbc.co.uk