Life on Mars? We may have found it -- and killed it
In 30 years, we've learned not all life depends on water
By TOM PAULSON
We may have already encountered Martian life about 30 years ago and accidentally killed it, according to a new analysis of NASA's Viking mission to Mars presented Sunday at a major astronomy conference in Seattle.
"It's a plausible hypothesis that explains the Viking results quite well," said Dirk Schulze-Makuch, an astrobiologist at Washington State University who studies the interplay of microbes, water and geology. Schulze-Makuch spoke Sunday at the American Astronomical Society meeting, which continues through Wednesday in Seattle.
When the Viking 1 and 2 Mars Landers dropped onto the Martian surface in 1976 to look for signs of living creatures, the scientific consensus was that they had failed to find any.
But Schulze-Makuch and his German colleague, Joop Houtkooper of Justus Liebig University, argue that the failure could have been more about how the scientific community defined life at that time. Back then, the WSU researcher noted, the definition assumed that any form of life would be based on water.
"Life does need a solvent, because otherwise you would just be a rock," Schulze-Makuch said Sunday. "But there is no reason the solvent always has to be water."
Since the Viking missions, he noted, bacteria and other microbes have been found in extremely hot and chemically toxic environments. Some of these "extremophiles" -- found in hellish places such as undersea volcanoes -- actually thrive on chemicals such as hydrogen peroxide that are hostile to most other living creatures.
A previously confusing finding on Mars by the Viking Landers was evidence of chemical oxidation. Scientists at the time assumed this meant the Martian surface was a highly reactive place, but further missions to Mars failed to find any evidence of oxidative chemistry.
Schulze-Makuch and Houtkooper suggest that the hydrogen peroxide detected by Viking could have come from killing Martian microbes that, like some peculiar creatures on Earth, use hydrogen peroxide the same way humans use water.
The Mars landers did all their chemical analyses by mixing samples with water -- a step that would have prompted a powerful chemical reaction in any microbe full of hydrogen peroxide, killing it and releasing the peroxide.
"Something had to oxidize for Viking to get those results," Schulze-Makuch said. Since nothing in Mars' soil or atmosphere appears capable of causing such a reaction, he said it's reasonable to suggest that it could have been a Martian microbe.
"It makes sense," the WSU astrobiologist said. This inadvertent destruction of microbes also would explain some of the other findings from Viking, he said, such as the lack of any detected organic compounds associated with living creatures.
Martian microbes, living on a cold planet, might be expected to use hydrogen peroxide because of its lower freezing point.
"It is interesting to note that the Viking experiments were conducted under too warm and wet conditions from the perspective of the hydrogen peroxide hypothesis for Martian life," the authors conclude in their report. "If the hypothesis is true, it would mean we killed the Martian microbes during our first extraterrestrial contact."
Schulze-Makuch said he and Houtkooper presented their findings in the hope that future missions looking for evidence of life on other planets or large moons will consider all possible forms of life. He said they already are talking with scientists working on the upcoming Mars Phoenix Mission, which plans to launch in August and then land near a polar region on Mars in 2008.
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