A Biological Solution to the Mystery of Methane on Mars

Under simulated Martian conditions, organisms on Earth can produce this critically important biomarker.

Ancient lake sediments in Gale Crater (pictured here by NASA's Curiosity rover) are rich in salts and clays, and so may be a prime location to explore for the possibility of methane-producing archaea in the near subsurface of Mars.

Methane, which can be a biomarker—or indicator of life—on Earth, has been detected by spacecraft orbiting Mars and by the Curiosity rover on the Martian surface. The question of its origin, though—particularly whether it’s of biological or chemical origin—has puzzled scientists for many years. Now a new paper by Debbie Maus from the Technical University Berlin and colleagues (including myself) provides a plausible mechanism for how methane can be produced biologically under certain environmental conditions found on Mars.

The science team put together an experimental chamber in which microbes obtained water exclusively by deliquescence—the process by which substances, mostly salts, absorb moisture directly from the atmosphere until they dissolve in the absorbed water and form a solution. This is critical because the Martian surface is nowadays devoid of liquid water.

Maus mixed different types of Martian analog soils with salts that microbes could use to draw water directly from the simulated atmosphere. Three different types of microorganisms were tested, all of them methanogenic archaea—single-celled microorganisms similar to bacteria that live in low-oxygen environments and produce methane as a result of their metabolism. The team found that two of the three tested organisms produced significant amounts of methane, particularly when exposed to salts and soils similar to some of the clay-rich soils found in ancient lakes on Mars.

The study may be even more relevant to the so-called Recurring Slope Lineae (RSL) on Mars, wet-appearing dark streaks that contain hydrated salts and tend to grow larger during warmer seasons. Some of the streaks have been seen in Gale Crater not far from Curiosity. Last year there was a heated discussion among project scientists whether to drive the rover close enough to the RSL to examine them with Curiosity’s instruments. They decided against it, mostly because of concerns about planetary protection—the rover was not sterilized sufficiently before launch to exclude the danger of contaminating these special sites with life from Earth. But the results from Maus and colleagues should make investigating the RSL even more of a priority—perhaps even with a new mission that can meet the tougher planetary protection requirements.

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