The puzzle of methane on Mars has taken an interesting new twist: For the first time, the gas has been detected within Martian meteorites. The finding adds another layer to the ongoing controversy over the origin of the methane, whether it is abiotic and geological or a potential biosignature of life, either past or present.
The methane was discovered inside the Martian meteorites by an international team of researchers. According to co-author Sean McMahon, a Yale University postdoctoral associate in the Department of Geology and Geophysics: “Other researchers will be keen to replicate these findings using alternative measurement tools and techniques. Our findings will likely be used by astrobiologists in models and experiments aimed at understanding whether life could survive below the surface of Mars today.”
The meteorites are pieces of volcanic rock originating from Mars; all six samples contained methane, which was measured by crushing the rocks and running the released gas through a mass spectrometer. The samples were taken from the interiors of the meteorites, to try to eliminate terrestrial contamination. Two non-Martian meteorites were also examined, which contained lesser amounts of methane. It is thought the methane was released from small trapped pockets of the gas inside the meteorites.
Meteorites such as these are known to originate from Mars since they contain gases in the same proportion and with the same isotopic composition as the Martian atmosphere, as measured by orbiters, rovers, and landers.
The research is a joint project led by the University of Aberdeen, in collaboration with the Scottish Universities Environmental Research Centre, the University of Glasgow, Brock University, and the University of Western Ontario.
The origin of the methane is of course a question the scientists would like an answer to. On Earth, methane can be created biologically by microscopic organisms (the primary source on our planet) or abiotically through volcanism or serpentinization—the interaction of heated water and rock. Even geologically produced methane would be interesting, since it would be evidence for on-going activity on Mars, most likely below ground. Any heat and/or water occurring below the surface would be beneficial for the possibility of other types of organisms.
“One of the most exciting developments in the exploration of Mars has been the suggestion of methane in the Martian atmosphere,” said University of Aberdeen professor John Parnell, who directed the research. “Recent and forthcoming missions by NASA and the European Space Agency, respectively, are looking at this, however, it is so far unclear where the methane comes from, and even whether it is really there. However, our research provides a strong indication that rocks on Mars contain a large reservoir of methane.”
Atmospheric methane has been observed on Mars by telescopes, orbiters, and rovers, most recently by the Curiosity rover. Preliminary data suggests it varies with the seasons and is episodic, concentrated in a few hotspots.
Even if the methane was not produced by life itself, it could still have provided a source of food energy for other organisms, known as methanogens on Earth. Similar microbes could possibly be surviving on Mars even today, below the surface where there is more warmth and protection from the harsh ultraviolet light from the Sun.
As McMahon also noted, “Even if Martian methane does not directly feed microbes, it may signal the presence of a warm, wet, chemically reactive environment where life could thrive.”
Lead author Nigel Blamey, a geochemist at Brock University in St. Catharines, Ontario, added, “We have not found life, but we have found methane that could potentially support microbes in the subsurface.”
From the paper abstract:
“The occurrence of methane in Martian rock samples adds strong weight to models whereby any life on Mars is/was likely to be resident in a subsurface habitat, where methane could be a source of energy and carbon for microbial activity.”
The research team will continue to study other Martian meteorites for additional clues as to how the methane became trapped inside them. If the isotopic ratio of the methane could be determined, it would help in narrowing down whether the source was biotic or abiotic. A related study from 2012 suggested that meteorites on Mars could produce methane themselves after being irradiated with ultraviolet light.
The paper, ‘Evidence for methane in Martian meteorites,’ was just published in Nature Communications. (Note: first written and received in September 2014, before the later confirmation of methane by the Curiosity rover).