IF LIFE exists on Titan, Saturn's biggest moon, we could soon know about it - as long as it's the methane-spewing variety. The chemical signature of microbial life could be hidden in readings taken by the European Space Agency's Huygens probe when it landed on Titan in January. Titan's atmosphere is about 5 per cent methane, and Chris McKay of NASA's Ames Research Center in Moffet Field, California, thinks that some of it could be coming from methanogens, or methane-producing microbes. Now he and Heather Smith of the International Space University in Strasbourg, France, have worked out the likely diet...