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It could be a blow for those who believe there’s life on the Red Planet. Spongy minerals at the surface, not living organisms, could be releasing Mars’s mysterious methane.

Methane gas, which chiefly emerges from biological processes, was identified on Mars in 2003. Since then, measurements by NASA’s Curiosity rover and others have shown that on any given day, methane exists in small but significant quantities, and occasionally jumps by a factor of 10.

Because it doesn’t hang around for long, something must still have been creating it.

“The cool thing about methane is that if you see it in the atmosphere that means it’s fresh – it’s being produced now,” says , a geologist at Indiana University in Bloomington.

But a new study is hypothesising that the methane is actually very old and has been locked away, perhaps for billions of years, occasionally pulsing into the atmosphere.

Cat litter

at the Marseille Observatory in France and his colleagues suggest such a storage reservoir could be composed of zeolites: sponge-like minerals with microscopic holes and channels that easily trap and release gases.

On Earth, zeolites naturally form within the voids of volcanic rock or in sedimentary deposits of volcanic materials, such as ash exposed to water. Their ability to trap gases within their holes and channels means they’re highly valued in industry. Cat litter, for example, uses zeolites to capture ammonium and methane and therefore lessen any unwanted stench.

Because their recipe requires volcanic sediments and water, their presence could indicate that ancient Mars had abundant water. Other geological evidence suggests the Red Planet had a watery past, supporting oceans and even tsunamis. And we’ve long known that Mars is littered with volcanic rock, and hosts the biggest volcano in the solar system. So it’s reasonable to expect that it supported zeolites, too.

Plodding on

“From the get-go, the hypothesis that zeolites can absorb the methane is a plausible one,” says , a planetary scientist who works with NASA’s Curiosity rover in search of zeolites.

Ming and others have been looking for zeolites on Mars for over 30 years. “It’s something we always look for every time we get a new analysis,” says , a California-based geologist at the Planetary Science Institute.

Unfortunately, we still haven’t found them. There has been one potential detection from orbit, but it hasn’t been confirmed. And despite searching for them on the ground, Curiosity has yet to find evidence for zeolites in Gale Crater.

“That doesn’t mean that it won’t,” Vaniman says. “The mission is still plodding along and we’ll be looking at more samples so there’s a chance that we might see some. And of course there’s a chance that Gale Crater is just not a place to find them.”

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