Martian Methane: Carbon compound hints at life

Evidence that parts of ancient Mars had oceans and might have supported some form of life in the past grabbed front-page headlines just a few weeks ago (SN: 3/27/04, p. 195: Available to subscribers at Signs of Water Flow: Oceans of data point to ancient Martian sea). But detection of the simple carbon compound methane in the Martian atmosphere by both ground-based telescopes and an orbiting spacecraft spotlights an even more intriguing possibility: There might be primitive life, even today, on the Red Planet.

By analyzing data collected by an earthbound telescope in 1999, Vladimir A. Krasnopolsky of the Catholic University of America in Washington, D.C., and his colleagues have measured Martian methane at 11 parts per billion. They’ve posted an abstract on the Internet and plan to announce their findings at a meeting of the European Geosciences Union in Nice, France, later this month, Krasnopolsky says.

Other planetary scientists announced last month that a spectrometer aboard the European Space Agency’s Mars Express spacecraft (SN: 2/21/04, p. 125: Available to subscribers at A view of Mars, European style) found methane at a concentration of about 10.5 ppb in the planet’s atmosphere. Vittorio Formisano of the Institute of Physics and Interplanetary Space in Rome presented the findings at a press conference last month in Paris.

The agreement of the ground-based–telescope results with the Mars Express data is “very reassuring,” says Krasnopolsky’s collaborator Toby Owen of the University of Hawaii in Honolulu.

Both sets of findings corroborate data that Michael J. Mumma of NASA’s Goddard Space Flight Center in Greenbelt, Md., presented last September at a meeting of the American Astronomical Society in Monterey, Calif. In 2003, using sensitive spectrometers at two large ground-based telescopes, Mumma’s team detected methane in the Martian atmosphere at concentrations ranging from 10 parts to 30 ppb.

Methane is an intriguing compound to find in the Martian atmosphere because it can’t survive there long. It takes sunlight only about 400 years to break down methane in the Red Planet’s atmosphere. The similar concentrations of methane detected over a 5-year period therefore suggest that the lost material is continuously replenished.

Krasnopolsky’s team calculates that comets striking Mars couldn’t deliver enough methane to replace what’s lost. It’s possible that the methane could be seeping out from underground reservoirs of material left over from the planet’s formation. Or, as on Earth, the organic compound could be a by-product of bacteria on or beneath the surface of the planet.

One of the locations where Mumma’s team found elevated methane lies above Meridiani Planum, the equatorial region where the NASA rover Opportunity found signs of a past ocean. That site might still contain underground deposits of water and, if so, “could potentially support active life forms,” Mumma notes.

Such musings are “all very hypothetical,” he emphasizes. But one test may discern whether the Martian methane has a biological origin. On Earth, methane made by living things has a ratio of carbon-12 to carbon-13 that’s slightly elevated compared with methane produced by nonbiological sources. If organisms on Mars were similar to those on Earth, they, too, would produce methane with an elevated ratio.

Members of Krasnopolsky’s team have proposed that a spectrometer sensitive enough to detect the slight difference in carbon ratio could be part of a Mars lander laboratory planned for launch in 2009. A space-based infrared spectrometer, proposed by Mumma’s team for launch at the end of the decade, would also have the capability to determine carbon-12–carbon-13 ratios.