The WIRED Guide to AliensDetermining whether the methane was produced by microbes or geological processes will be tricky, but that’s part of the reason why Giuranna and other scientists studying Mars are so excited about Curiosity’s new methane detection. On Sunday, NASA scientist Paul Mahaffy said that “with our current measurements, we have no way of telling if the methane source is biology or geology, or even ancient or modern.” But a suite of hyper-precise instruments orbiting Mars hundreds of miles above Curiosity might be able to help answer these questions.In a case of cosmic good fortune, the Mars Express orbiter happened to be performing spot tracking observations of the Gale crater right around the time Curiosity detected the methane spike. Spot tracking focuses the satellite on a specific area as it passes overhead and allows its onboard instrumentation to perform hundreds of measurements during its brief flyby. This allows scientists to create data averages, rather than relying on single observations, to get a more accurate picture of what is happening in the Martian atmosphere. In this case, the Mars Express orbiter was doing spot tracking 20 hours before Curiosity’s methane detection, as well as 24 and 48 hours after the detection.As an added bonus, the ExoMars Trace Gas Orbiter also was performing atmospheric observations at around the same time as Mars Express, but at a higher latitude. Together these measurements will be used to confirm Curiosity’s detection of a methane spike and add constraints that will help scientists determine things like when the methane release started and how long it lasted. But the real prize, says Giuranna, would be determining how the methane is produced.This involves analyzing the ratio of methane and its isotopologues, which are methane molecules in which one of the constituent atoms—carbon or hydrogen—has a different number of neutrons from a ‘normal’ methane molecule. Based on the ratio of methane and its isotopologues, Giuranna says scientists can get an idea of the process that created it. Even though there is hardly any methane in the Martian atmosphere, he says the most recent spike observed by Curiosity, which registered 21 parts per billion, would be more than enough for the Trace Gas Orbiter to tease apart these methane ratios and point to their origin.We’re probably going to have to wait a few weeks before scientists can complete their analysis of the data from the Mars Express and the Trace Gas Orbiter. Neither of the orbiters have relayed their data back to Earth yet and there’s a chance that the Trace Gas Orbiter didn’t register any methane. Indeed, the first major data dump from the Trace Gas Orbiter, published by Giuranna and his colleagues earlier this year, showed that the satellite hadn’t detected any methane in the Martian atmosphere. Giuranna says there are many possible explanations for such a discrepancy, such as a “destruction mechanism” capable of removing methane from the atmosphere.If the Trace Gas Orbiter didn’t register a methane spike this time around, Giuranna says they’ll probably have to wait for the sensitive instruments aboard the ExoMars rover to hit the ground on the Red Planet in 2020 before he and his colleagues can dig deeper into the origin of Martian methane.
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“We need to have process representation to understand these mechanisms,” says Eric Kort, an atmospheric scientist at the University of Michigan, “so we can say, for example, with certain changes to temperature and the hydrological cycle, we’d expect methane emissions to increase by X amount.” Without that understanding, Kort suggests, we’re unable to answer some important questions about what looms ahead.