Does Mars Methane Indicate Life Underground?
for National Geographic News
|October 7, 2004|
Data obtained by the Mars Express probe that is currently orbiting the red planet show that water vapor and methane gas are concentrated in the same regions of the Martian atmosphere, the European Space Agency recently announced.
The finding may have important implications for the possibility that microbial life could exist on Mars. If microbes are making methane in the Martian atmosphere as part of their living process, they would rely on water.
Some scientists remain skeptical, however. They are not convinced that the new methane measurements are real and statistically valid. Even if the overlap exists, they say, it could just as easily be explained by other processes.
Vittorio Formisano of the Institute of Physics and Interplanetary Science in Rome, Italy, lead the team that made the recent announcement. In March the same researchers said they had detected methane in the Martian atmosphere. The scientists used the Planetary Fourier Spectrometer (PFS) on Mars Express, an instrument that maps infrared radiation on Mars.
Now new PFS data shows that at 10 to 15 kilometers (6.2 to 9.3 miles) above the Martian surface, water vapor is well mixed and uniform. Close to the planet's surface, however, water vapor is two to three times more concentrated in three equatorial regions than in other areas.
The data also shows concentrations of methane in the same areas where water vapor and underground water ice are more concentrated. A water-ice layer a few tens of centimeters (8 to 12 inches) below the surface was detected by NASA's Odyssey spacecraft, which is also orbiting Mars.
"This overlap [of methane and water vapor] points to a common underground source in the same regions," Formisano said in an e-mail interview.
Formisano stresses that an underground source doesn't prove there is microbial life. The methane could be a byproduct of volcanic gassing. Or it could be the chemical reaction between water and rocks in the soil and crust.
However, there is a possibility that the methane is produced by organisms called methanogens, which are microbes that produce methane as a waste product of their life process. The gas would be released to the surface and into the atmosphere.
Scientists have speculated that the methane-producing bacteria may live in water below the presumed ice table.
The new results suggest that whatever is producing the methane is ongoing, because methane can only survive in the Martian atmosphere for a few centuries.
Some scientists are skeptical about the detection of methane on Mars. Bruce Jakosky, a planetary geologist at the University of Colorado in Boulder, has studied atmospheric water on Mars for 25 years. He says he is not yet convinced that the methane measurements are real and statistically valid.
"Also, there is nothing in the water vapor measurements to suggest that there's a need to invoke a subsurface source," he said. "The distribution of water vapor is controlled primarily by the circulation of the atmosphere and the motions of the wind. If the water vapor and methane correlate, I would be more inclined to think the methane is also being redistributed by the wind."
Jakosky says there would have to be a "humongous" source of methane for the gas to be hovering over one region without being redistributed. "It's just not physically plausible," he said.
The evidence for an underground ice table around the Martian equator is also controversial. This is based on Odyssey's detection of hydrogen atoms in the top layer of the soil. Some experts interpret the hydrogen as being locked in ice and others say it could come from minerals affected by water in the past.
Formisano presented his results on September 20 at the International Mars Conference in Ischia, Italy. But the findings have not been published yet, which Jakosky says makes it difficult for the science community to evaluate.
"It's frustrating that we increasingly seem to be doing science by press release," Jakosky said. "It's time for these guys to publish their results."
Mars is the planet in our solar system that most closely resembles Earth. It has a rocky surface, perhaps making it easier for life to gain a foothold.
Earlier this year, NASA announced that its roving robot Opportunity had found evidence that water once soaked the planet Mars. Pictures from the rover's panoramic imager revealed salt-laden sediments that would have been shaped by flowing water or maybe a great Martian lake or sea.
Mars may not have only been wetter in the past, but could have had a denser atmosphere. There is the possibility that life arose on Mars, only to die out as conditions on the planet changed. Some researchers have suggested that future searches for life should focus on extinct, rather than current, life.
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