The Mars Curiosity rover is sniffing methane in the Martian air but NASA researchers suspect that the distinctive gas—often a sign of life on Earth—may be leaking from buried deposits and not from microbes living on the Red Planet today, space agency scientists said Thursday. The traces of methane on Mars are tantalising to biologists eager for evidence of life. Astronomers using Earth-based telescopes and satellite readings first started detecting faint plumes of methane on Mars more than a decade ago. But no one could tell whether the gas was a by-product of microbial life, the result of geological reactions or a side effect of meteoroids and cosmic dust raining down on the planet.
In the new research, scientists analysed about six years of atmospheric measurements collected by the NASA robot rover and concluded that Martian methane rises and falls with the seasons, peaking near the end of summer in the planet’s northern hemisphere. On Mars, methane levels ranged between 0.24 to 0.65 parts per billion, compared with levels of about 1800 parts per billion in the air on Earth, the scientists said. “That is a huge change, completely unexpected,” said Christopher R. Webster at the National Aeronautics and Space Administration’s jet propulsion laboratory in California. He leads the team that is sampling the Martian air with a sensor aboard the rover called the tunable laser spectrometer, an instrument specially designed for measuring the gas on Mars.
The researchers discussed their findings at a NASA briefing Thursday and published their research in Science. After ruling out several potential sources, the researchers suggested that methane might be leaking from water-based crystals called clathrates buried in the cold Martian soil. Seasonal changes in temperature could cause the variations in methane levels the rover detected. “The idea that best fits our data is subsurface storage,” said Dr Webster. “Way under the surface of Mars there is methane trapped. We don’t know if that methane is modern or if it is ancient.” In a related finding also published in Science, space agency scientists said that the Curiosity rover found organic molecules contained in samples of three-billion-year-old mudstone on Mars. There is no way, though, to determine if it is evidence of ancient Martian life or not, the researchers said. “Are there signs of life on Mars?” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at NASA headquarters. “We don’t know, but these results tell us we are on the right track.”
Credit: Robert Lee Hotz for The Wall Street Journal, 7 June 2018.