astroengine writes "The first planet-wide studies of methane on Mars — incorporating billions of measurements made by NASA's Mars Global Surveyor spacecraft — shows gas concentrations peak in autumn and plummet in winter. Scientists have found significantly higher methane concentrations in the Tharsis, Elysium and Arabia Terrae regions. Tharsis and Elysium are home to Mars' most massive volcanoes and Arabia Terrae has large quantities of subterranean frozen water. This indicates the gas could be generated by geological or biological activity. 'It could be geology or biology, but it is not coming from another source. There is a seasonal pattern, so it could only be a local origin,' Sergio Fonti, with Italy's Universita del Salento, told Discovery News."