Pearl, 9.35pm Ah, the final frontier. What happens if we mess up the Earth to such an extent that humans have to colonise other planets and stars? This programme examines the possibilities. The main problem would seem to be that the nearest star, after the sun is not particularly handy. Voyager, the Nasa space probe, is on its way to the outer limits of the galaxy at 40,000km/h, but even shifting at that speed it will take 25,000 years to get to our closest star. One way of reaching these distant destinations quicker could be solar sails. Gossamer-light and spanning hundreds of kilometres, these vast, delicate ships could hurtle through space pushed by the light from our sun. This is the mode of transport envisaged by Les Johnson of Nasa at any rate. Another problem with staying on Earth is the sun, now 30 per cent hotter than it was at the time of the formation of the Earth and getting warmer. In half a billion years, the sun will be so hot the Earth will be uninhabitable. Could neighbouring Mars be the next place mankind makes home? Informative but frightening. Presented by Sam Neill (above).