"One of the best chances for solving Mars's methane mystery may have been lost. The Planetary Fourier Spectrometer (PFS) on board the Mars Express orbiter seems to be broken, perhaps for good."
"In 2004, the PFS found that methane averaged about 10 parts per billion in Mars's atmosphere, suggesting that more than 100 tonnes of the gas is released from the surface each year. That same year, Mike Mumma of NASA's Goddard Space Flight Centre in Maryland spotted levels of 250 parts per billion using a telescope in Hawaii. This week he told an American Astronomical Society meeting in Cambridge that he had spotted levels of 44-63 parts per billion from a different part of the planet."