Martian methane

A group of astronomers headed by Michael Mumma of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has reported in substantial spatial and temporal detail the first definitive detection of methane (CH₄) in the atmosphere of Mars. The Martian atmosphere consists overwhelmingly of oxidized gases such as carbon dioxide; reduced gases such as methane were known to be rare. In 2003 and 2006, using two telescopes on Mauna Keain Hawaii, the group observed much of the planet’s surface spectroscopically at IR wavelengths to confirm the presence of methane and determine its seasonal and “ariegraphic” distribution. (A Martian season is about six months long.) Mumma and company found extended plumes of methane that appear to emanate at substantial rates from three localized sources in the northern summer (see the figure). They suggest that the summer emergence results from the unfreezing of pores and fissures connecting with underground accumulations of the gas, and that oxidation in winter dust storms accounts for the very meager methane signal remaining at the start of spring. Is the methane biogenic? On Earth 90% of it is, the rest coming from inorganic geochemistry. If it is biogenic on Mars, it could be a vestige of life long extinct or a sign of ongoing life in warm precincts deep underground, perhaps energized by molecular hydrogen from the hydrolysis of water by radioactivity. Isotopic ratios measured by future IR missions to Mars should help determine the methane’s origin. (M. J. Mumma et al., Science Express 323 , 1041, 2009, http://dx.doi.org/10.1126/science.1165243 .)