A NASA robotic rover on Mars has detected unusually big seasonal changes in methane, boosting the hopes of some scientists that the planet is home to alien life.
Curiosity – formally known as Mars Science Laboratory – found the gas is more abundant in the atmosphere during late summer at its site in the martian northern hemisphere.
Plumes of methane have previously been detected on Mars by telescopes on Earth. Their origin sparked a debate among scientists because the gas can be produced by rocks as well as microbes.
On Earth methane comes mainly from microbes, including those living in the stomachs of cows and sheep, who belch it into the air.
Mars’s surface is sterile because it has no protection from a deadly bombardment of radiation from space. But some astronomers believe that living organisms could survive underground, where they would be shielded from the radiation.
Methane can also be generated by hydrothermal reactions with rocks. However, the scientists are puzzled because the amount detected increases more than they would expect from such processes.
Chris Webster, who leads the methane-sensing instrument on Curiosity, told Science, the journal of the American Association for the Advancement of Science: “We’re left trying to imagine how we can create this seasonal variation.”
Webster, who is based at NASA’s Jet Propulsion Laboratory in California, has been measuring the amount of methane over two martian years since the rover landed in 2012. A martian year lasts about two Earth years.
He said the increase in the amount of methane in late summer was three times larger than a geological mechanism could explain. He said it was possible that more methane gets released when the rocks are warmer.
But Mike Mumma, a planetary scientist at NASA’s Goddard Space Flight Center in Maryland told Science that a biological explanation was “one that no one talks about but is in the back of everyone’s mind.” He added: “You’d expect life to be seasonal.”
European scientists might be able to solve the puzzle. They have experiments on the European Space Agency’s ExoMars Trace Gas Orbiter spacecraft which arrived at Mars in October 2016.
In April this year, the probe will settle into its final orbit and begin to make detailed mapping of the amount of methane in the Red Planet’s atmosphere.
Related: Our guide to Mars
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