NASA's Curiosity rover has detected a 10-fold spike in atmospheric methane on Mars, and organics in a rock powder sample. "This temporary increase in methane -- sharply up and then back down -- tells us there must be some relatively localized source," said Sushil Atreya of the University of Michigan, Ann Arbor, and Curiosity rover science team. "There are many possible sources, biological or non-biological, such as interaction of water and rock."
Curiosity also detected different Martian organic chemicals in powder drilled from a rock dubbed Cumberland, the first definitive detection of organics in surface materials of Mars. These Martian organics could either have formed on Mars or been delivered to Mars by meteorites.
Methane is considered a biosignature gas under Martian conditions -- i.e. an indicator of possible biological activity. It is unstable in the Martian atmosphere, breaking down quickly under ultraviolet light. This means that some source must be producing it at the present time. The primary source of methane on Earth is the biochemical pathway methanogenesis, which occurs in some Archaea. Methanogenesis is an extremely ancient metabolic pathway, which was likely present on the early Earth. However, methane can also be generated nonbiologically by olivine rock interacting with water.
Researchers used Curiosity's onboard Sample Analysis at Mars (SAM) laboratory a dozen times in a 20-month period to sniff methane in the atmosphere. During two of those months, in late 2013 and early 2014, four measurements averaged seven parts per billion. Before and after that, readings averaged only one-tenth that level.
"That we detect methane in the atmosphere on Mars is not an argument that we have found evidence of life on Mars, but it is one of the few hypotheses that we can propose that we must consider as we go forward in the future," Dr. John Grotzinger, Curiosity project scientist at the California Institute of Technology in Pasadena, said on Dec. 16 in a news briefing at the American Geophysical Union's convention in San Francisco.
References:
Webster et al., Mars methane detection and variability at Gale crater
Mahaffy et al., The Imprint of Atmospheric Evolution in the D/H of Hesperian Clay Minerals on Mars