One of the clearest indicators yet of the presence of life on Mars has been discovered as scientists release the results of a 7-year study of the Martian atmosphere. Using telescopes in Hawaii, researchers detected up to 19,000 tonnes of methane on the planet. Most exciting of all, the methane appeared to build up in the Northern hemisphere during summer months on the planet, which would also be indicative of some kind of biological process. However, caution is being exercised, since it is not impossible that the process producing the methane is geological. We might be seeing something called serpentinisation, which occurs when rocks rich in certain minerals react with water, releasing methane, but the odds certainly now seem to be 50/50 that some kind of primitive microbes are thriving on Mars.