A little over a year ago, NASA said there was no life on Mars. Now it turns out that we may have discovered life on Mars over 30 years ago, from soil samples taken during the Viking landings. We just didn't analyze them correctly.
Even as new missions to Mars seek evidence that the planet might once have supported life, we already have data showing that life exists there now?data from experiments done by the Viking Mars landers in the late 1970s, according to US researcher Dirk Schulze-Makuch and German researcher Joop Houtkooper. Schulze-Makuch says, "I think the Viking results have been a little bit neglected in the last 10 years or more, but actually, we got a lot of data there." Recent findings about Earth organisms that live in extreme environments and improvements in our understanding of conditions on Mars have given astrobiologists new ways of looking at the 30-year-old data.
The researchers think that Mars is home to microbe-like organisms that use a mixture of water and hydrogen peroxide as their internal fluid. Such a mixture would provide at least three clear benefits to organisms in the cold, dry Martian environment: Its freezing point is as low as almost negative 60 degrees Celsius, and below that temperature it becomes firm but does not form cell-destroying crystals, as water ice does. Also, H2O2 is hygroscopic, which means it attracts water vapor from the atmosphere?a valuable trait on a planet where liquid water is rare.
Schulze-Makuch says that scientists working on the Viking projects weren't looking for organisms that rely on hydrogen peroxide, because at the time nobody was aware that such organisms could exist. The study of extremophiles, organisms that thrive in conditions of extreme temperatures or chemical environments, has taken off since the 90s, well after the Viking experiments were conducted. He and Houtkooper think that that hydrogen peroxide-containing organisms could have produced almost all of the results observed in the Viking experiments.
Hydrogen peroxide is a powerful oxidant. When released from dying cells, it would sharply lower the amount of organic material in their surroundings. This would help explain why Viking's gas chromatograph-mass spectrometer detected no organic compounds on the surface of Mars.
It would also explain the results of the Labeled Release experiment, in which samples of Martian soil (and the organisms within it) were exposed to water and a nutrient source including radiolabeled carbon. They showed rapid production of radiolabeled CO2 which then leveled off. Schulze-Makuch said the initial increase could have been due to metabolism by hydrogen peroxide-containing organisms, and the leveling off could have been due to the organisms dying from exposure to the experimental conditions.
There is also the possibility that the tests killed the organisms they were looking for. This is consistent with the results of the Pyrolytic Release experiment, in which radiolabeled CO2 was converted to organic compounds by adding samples of Martian soil. Of the seven tests done, three showed significant production of organic substances and one showed much higher production. The variation could simply be due to patchy distribution of microbes. Perhaps most interesting was that the sample with the lowest production?lower even than the control?had been treated with liquid water. Schulze-Makuch says, "If the hypothesis is true, it would mean that we killed the Martian microbes during our first extraterrestrial contact, by drowning?due to ignorance.
"We can be absolutely wrong, and there might not be organisms like that at all, but it's a consistent explanation that would explain the Viking results." The Phoenix mission to Mars, scheduled for August, 2007, offers a good chance to further explore their hypothesis.
Art credit: gimp-savvy.com
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