From Fox News:
The organisms — called methanogens — are suspected to have been living in water beneath underground ice, where they are disgorging tons and tons of methane.
On Earth, methane is produced in massive quantities by animals such as cows, sheep and goats, as well as by geological processes.
Giant telescopes from Earth and NASA's Mars Reconnaissance Orbiter have spotted a haze of the gas surrounding Mars, and according to some scientists this can only point to the presence of life on Mars.
“Methane is a product of biology,” British Mars expert Professor Colin Pillinger told the London tabloid The Sun Wednesday night.