A leading European Space Agency scientist has reignited the debate about life on Mars by claiming that gas detected in the planet's atmosphere can only be explained by the presence of living organisms. Vittorio Formisano at the Institute of Physics and Inter planetary Science in Rome says measurements from the agency's Mars Express spacecraft, which has been orbiting the planet since December 2003, suggest there is far more methane there than previously thought. Although some scientists believe the gas might be produced by volcanic activity, Dr Formisano said Martian soil microbes were the most likely source