The Martian methane remains a mystery. "In the coming weeks the European Space Agency and NASA are to give the green light for the first joint missions to pursue the exploration of Mars. Despite the many spacecraft orbiting the red planet and the landers on its surface, Mars still holds many mysteries. One of them is the presence of methane discovered five years ago in its atmosphere by ESAs Mars Express and by two telescope observations from Earth. Since then scientists have been investigating the nature and origin of this methane which could, perhaps, be produced by living organisms - but it still remains a great mystery. This A & B-Roll includes interviews with principal scientists working on the subject, including Olivier Witasse, Mars Express Project Scientist at ESA, Vittorio Formisano, PFS Principal Investigator, and Sushil Atreya, leading authority on planetary atmospheres.