Almost no matter where the methane comes from, it’s an intriguing discovery. If you dropped a molecule of methane into the atmosphere of Mars, it would survive about 300 years—that’s how long, on average, it would take for solar ultraviolet radiation and other Martian gases to destroy the molecule. By rights, the Martian atmosphere should have been scrubbed of its methane eons ago. So, the methane we see must come either from a source that is producing methane today or from a subsurface reservoir that is venting methane produced sometime in the past. On Earth, 95 percent of methane is biological in origin. The class of bacteria known as methanogens feeds on organic matter and excretes methane. They populate our planet’s wetlands, which account for nearly a quarter of the methane present in the Earth’s atmosphere globally. Cows’ gut bacteria are the second largest producers. It is the possibility of microbial life that has propelled the search for methane on Mars.
But even if the methane there comes from geologic processes, it would give us a profound new respect for what looks outwardly like a geologically dead world. Methane can be produced by the geochemical process of serpentinization, which is widespread in Earth’s crust, especially at warm and hot hydrothermal vents on the ocean floor known as Lost City and Black Smokers. This process requires a source of geologic heat as well as liquid water. Those happen to be two main ingredients of life, as well. [...]
Surprisingly, during a single two-month period, four sequential observations reported a spike of 7 ppbv. These values were much too high to explain by comets, meteorites, or dust. They must have been of Martian origin—perhaps a burp from a relatively small and localized subsurface source to the north of the landing site. The Martian winds would blow that methane away over several months, explaining why the signal went away when it did. Alternatively, that pulse could be from a distant and much bigger source, which would require some other unknown mechanism to remove methane quickly. Like the earlier observations of plumes, the spikes seen by Curiosity remain a tantalizing clue to a still-enigmatic Mars.
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