No one is suggesting that Mars has flatulent cows, but a new study shows that the Red Planet, like Earth, spews methane. Researchers say it's possible that the gas could be generated by bacteria living beneath the Martian surface.
The methane emissions, observed over three Mars years (seven Earth years), come from three locations and vary with the seasons--strongest in Martian summer and weakest in winter, Mike Mumma of NASA's Goddard Space Flight Center in Greenbelt, Md., and his colleagues report online January 15 in Science.
Methane is a fragile compound, and the variations in its concentration indicate that methane in the Martian atmosphere lasts for less than one Earth year and is constantly being replenished, Mumma says. That suggests that even if the planet isn't biologically active, some unknown geological process is very much alive, continually releasing methane into the air.
To detect the methane, Mumma and colleagues monitored Mars from Earth, using three ground-based spectrometers to spread infrared light into its component wavelengths. Using a new algorithm that removed extraneous signals from Earth's atmosphere, the team detected three absorption features that conclusively prove the presence of methane plumes on Mars.
"Mumma and his team have been painstakingly careful," comments astrobiologist Christopher Chyba of Princeton University. "The reward is that we have observations of methane that show variations over season and by location."
The European Space Agency's orbiting Mars Express had previously found hints of methane, but the craft's spectrometer isn't sensitive enough to make a definitive measurement, says Jack Mustard of Brown University in Providence, R.I.
In 2003, when the observations began, one of the plumes released about 19,000 metric tons of methane. The plumes were detected over locales that show either evidence of ancient ground ice or the flow of liquid water, including the Nili Fossae region, an area east of Arabia Terra and the southeast quadrant of an ancient volcano called Syrtis Major.
Another team recently reported that Nili Fossae contains carbonates, which form only when liquid water is present. …