October 24th, 2012 by James Ayre
NASA’s Mars rover Curiosity has been the subject of rumors lately –specifically, that it may have discovered methane on the planet (Curiosity is the first rover with the ability to do so).
Methane has been previously detected on Mars from a variety of different satellites and telescopes, but until now none of the rovers have been equipped to test for it from the surface.
So far, NASA hasn’t said anything about whether or not it has detected any, leading to some recent speculation that there is an announcement coming.
The previous long-distance observations of methane on Mars haven’t allowed for the kind of detailed analysis that Curiosity is capable of. Curiosity will be able to characterize in great detail whether methane is a constant presence (geologic origin) or more variable (possible organic origin); and the isotope ratio, which can also give insight into its origin.
“Curiosity is toting the Sample Analysis at Mars instrument suite, or SAM, an onboard lab that accounts for more than half of the science payload on the 1-ton rover. Though SAM’s components would ordinarily fill a laboratory here on Earth, they have been miniaturized to roughly the size of a microwave oven in order to fit inside the robot,” Space.com writes.
“SAM’s duty is to analyze gases that are either ‘sniffed’ directly from the Martian atmosphere (which it has done several times) or extracted from soil or powdered rock samples by heating or chemically treating the samples.
“Provided by NASA’s Goddard Space Flight Center, SAM is on the search for compounds of the element carbon, including methane, that are associated with life. SAM will also explore ways in which those compounds are generated and destroyed in the Martian ecosphere.”
“The key question about methane on Mars is not its presence, but its variability,” said Chris McKay, space scientist and Mars specialist at NASA’s Ames Research Center in Mountain View, Calif.
It’s been previously shown that methane can be produced by organics that are falling onto the surface of Mars from space, and then being hit with ultraviolet light.
“So there will certainly be methane at some level, possibly well below one part per billion,” McKay said.
“But what was surprising in the Mars Express results and the Earth-based observations was the variability,” he added, referring to the European Space Agency’s Mars Express orbiter. “Methane on Mars should have a lifetime of 300 years and should not be variable. If it is variable, this is very hard to explain with present theory. It requires unexpected sources and unexpected sinks.”
With regards to Curiosity’s SAM instrument, the main thing is the long-term tracking of methane, mapping the variability.
“If it’s constant, then this can be reconciled with normal processes and a meteoritic source of organics. If it’s highly variable, then all bets are off.”
“Methane should be there,” said astrobiologist Dirk Schulze-Makuch of Washington State University in Pullman.
This view is based on previous independently-done studies that have shown that methane is almost always associated with biological activity or biological activity in the distant past.
“Methane is really quite a rare gas in hydrothermal/volcanic exhalations; thus a methane detection with the rover would be exciting and could point to biology, especially if detected in relatively large amounts,” said Schulze-Makuch.
“Even more exciting,” Schulze-Makuch said, “would be if the carbon in the methane has an isotopic fractionation that is consistent with biology. If the methane is produced by organisms — for example, metabolism — then we expect a shift to the lighter isotopes. In essence because life is lazy, same effect, with less work compared to inorganically produced carbon.”
It’s currently unknown whether any methane detected on Mars will be present in large enough quantities to determine the isotope ratio.
“But it would be very exciting. To try and determine the isotopic fractionation and a good inorganic baseline for carbon would be the next step in my view.”
Image Credits: NASA/JPL-Caltech; NASA
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