Professor Paul Murdin assesses whether life really could exist outside our planet. If it does, what form might it take, and could it be as advanced as life on Earth? Or, are we simply alone in the universe?

Prof Murdin is former president of the European Astronomical Society. He has been director of the British National Space Centre and is a fellow of the Institute of Astrononmy at Cambridge University and visiting professor at Liverpool John Moores University. His works include Catalogue of the Universe and Secrets of the Universe.