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Take a Whiff of Mars

photography by Chris Robinson

A gas that smells like rotten eggs wafts over Mars, shifting with the seasons. Science has known about it for years.

But why the planet’s methane levels vary with the seasons has never been fully been explained – until now.

A York University planetary scientist conducting research at Gale Crater – the location of NASA’s Curiosity rover – has uncovered a link between the surface rocks and methane in the Martian atmosphere, accounting for both the origin and oscillation of the strange odour.

“This study shows that the methane seen by the Curiosity rover likely originates in the subsurface of Mars,” says John Moores, an associate professor in York’s Department of Earth & Space Science & Engineering who conducted his research in collaboration with NASA’s Curiosity rover science and operations team. 

“It helps to explain the mechanism that produces the seasonal cycle in methane levels that the Curiosity rover recorded on Mars.”

Previous research has shown that methane levels vary from season to season at Gale Crater, a site whose unique environment makes it easier to detect chemical seeps than elsewhere on the planet. It is now understood that there is more methane in the Martian atmosphere when it is warmer and less when it is cooler, a repeatable pattern Moores drew on for his own study. 

To track the movement of methane through the planet’s subsurface, Moores led an international team of researchers in developing a computer model that could compare how much methane found its way into the Martian atmosphere to the amounts measured by the Curiosity rover’s SAM-TLS sample analysis instrument. 

Armed with this data, the researchers then adjusted the enthalpy of adsorption – a measure of how much methane was “stuck” on the planet’s regolith (a soil made up of broken rocks) – until able to produce a match. The findings were startling. 

“We expected these processes to operate in a similar way on Mars because they certainly happen on Earth, so that’s not surprising,” Moores says. “But what did surprise us was how closely everything matched once we started to change how the soil and the methane interacted with one another.” 

Methane emissions on Earth are the exhalations of life, rising from agricultural barns housing animals and from bacteria-laden swamps. Which begs the question: does the presence of the gas on barren Mars indicate there’s life there after all? 

Moores won’t comment. 

“Our study is agnostic about what is actually producing the methane. There are many models that don’t require any biological activity at all,” he says. 

“But those models that do have a biological origin to the methane typically need those organisms to be underground where they would be protected from the intense radiation environment, aridity and cold of the Martian surface. We still have more work to do for testing any hypothesis.”     

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