While the smell of methane is not always to be welcomed here on Earth, methane is usually a strong indication that something organic or animal related is going on.  Consequently, it was with regret that NASA/JPL scientists working on data from the Mars Rover Curiosity noted that the gas analyser which uses laser spectrometry to examine the constituents of the Martian atmosphere had not found signifciant amounts of methane, with its concentration, at best, being at only circa 3 parts per billion.  

Scientists had been hoping that the continous presence of significant amounts methane would be a key signature indication that life forms were currently or had been recently on the planet. Methane concentrations degrade naturally under ultra violet light.  So while one-off volcanic eruptions could cause methane concentrations to rise temporarily, for continously stable methane concentratons in the atmosphere, life would have to be present.  Measurements of the Martian atmopshere will continue.