The Enigma of methane
The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, Vittorio Formisano, Istituto di Fisica dello Spazio Interplanetario CNR, Rome, and the rest of the instrument team saw a puzzling signal. As well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane.
On Earth much of the methane in our atmosphere is released by evolved life forms, such as cattle digesting food. While there are ways to produce methane without life, such as by volcanic activity, it is the possible biological route that has focused attention on the discovery.
The discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. ESA plans to find out which it is. Either outcome is big news for a planet once thought to be biologically and geologically inactive.
The Mars Express detection of methane is not an isolated case. While the spacecraft was en route, two independent teams of astronomers using ground-based telescopes started to see traces of methane. After five years of intensive study, the suite of observations all confirmed the discovery and presented planetary scientists with a big puzzle.
The 2016 ExoMars Trace Gas Orbiter is the first in a series of Mars missions to be undertaken jointly by the two space agencies, ESA and Roscosmos. A key goal of this mission is to gain a better understanding of methane and other atmospheric gases that are present in small concentrations (less than 1% of the atmosphere) but nevertheless could be evidence for possible biological or geological activity.