NASA's Mars rover Curiosity's discovery of organic compounds in the ground and plumes of methane in the air opens two potentially related investigations into whether or not the planet most like Earth in the solar system also hosted life.
The methane spikes, announced by scientists at a press conference Tuesday, may be the easier issue for rover scientists to tackle since it is basically a waiting game to see if the plumes reoccur.
Between late November 2013 and late January 2014, samples of the atmosphere collected and analyzed by Curiosity showed a 10-fold increase in concentrations of methane, a gas which on Earth is strongly tied to life.
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When the next sample was taken two months later, the gas was gone, a mystery in and of itself since methane gas should last for 300 years in the Martian atmosphere.
The rover, which is now exploring the base Mount Sharp, a three-mile high mound of sediment rising from the floor of its Gale Crater landing site, will continuously sniff the air for methane, said lead scientist John Grotzinger, with the California Institute of Technology in Pasadena.
If higher concentrations are detected, the rover's onboard chemistry lab will attempt to enrich the samples by scrubbing away atmospheric carbon dioxide, leaving more methane for analysis. Detailed studies of how quickly the methane dissipates could provide clues about its origin and what causes its periodic release. For now, scientists suspect the methane burp came from somewhere in or near Gale Crater.
If a very large burst of methane was detected, scientists could attempt to chemically analyze its isotopic composition, which again might provide insight into whether it was produced by past or present day microbes, or if it is a byproduct of geochemical processes, such as meteorite impacts or hydrated mineral transformations.
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The emissions show that "Mars is currently active and that the subsurface is communicating with the atmosphere," Curiosity participating scientist Sushil Atreya, with the University of Michigan at Ann Arbor, said at the American Geophysical Union press conference.
The scientists had news about ancient Mars too, revealing – after 18 months of analysis – that chlorobenzene organics were detected in samples drilled out from an ancient mudstone called Cumberland.
"We knew we were on to something but it's hard to know for sure that it wasn't a false positive until you've analyzed more rocks," Grotzinger said. "You don't want to get faked out if it was contamination from the instrument."