Could we have missed life on Mars?
Thirty years after NASA's Viking mission carried out a series of experiments on Mars, new research suggests that scientists too quickly dismissed possible signs of life there.
Back in July and August of 1976, Viking 1 and 2 became the first crafts to land successfully on another planet. Researchers immediately carried out tests on samples of soil that had been scooped up and dumped into test chambers inside the landers.
One of those tests, called the labeled release test, produced results at both landing sites that met all the agreed-on criteria for a positive detection of living microbes in the Martian soil. They showed that nutrients added to the soil had been broken down and given off as carbon dioxide gas, which is what happens when microorganisms eat the nutrients.
When those results first came in, the scientists were excited about the apparent signs of life.
But they were soon baffled by contradictory results from another test, called a gas-chromatograph mass spectrometer, designed to analyze the chemical composition of the soil. That test seemed to show that there was no organic material -- compounds containing the element carbon, which form the basis of all known life.
Seeing those results, most people gave up on the possibility of life on the surface of Mars.
The new research, published last week in the Proceedings of the National Academy of Sciences, used the same spectrometer test on several Mars-like environments on Earth -- and found no signs of organic compounds here, either.
"Our work clearly shows that the argument that was the most compelling to rule out the possibility of life on Mars now was wrong," said Rafael Navarro-González of the National Autonomous University of Mexico, who conducted the new research. "So this opens up the possibility that there could be biological activity on Mars."
Gilbert Levin, who designed and ran the labeled release test, said he had always doubted the results of the spectrometer test and felt that his initial readings were right. The new study, with which he was not involved, "drives a spike in" the idea that the spectrometer test results invalidate the life-detection evidence.
A Russian mission in 1996 was supposed to check the results of the Viking tests, but it crashed into the desert in northern Chile shortly after takeoff. The current American mission to Mars, which logged its 1,000th Martian day last week, has looked for signs of surface water -- which it hasn't found -- but is not equipped to look for signs of microbial life.
Navarro-González said his results make it a top priority to conduct further tests on Mars to answer the question once and for all.
A device on the Phoenix mission slated for launch next year could investigate the presence of organic compounds. And it could also identify exactly what those organic molecules are, which might provide additional evidence for living organisms, if they are present.
If we do find molecules indicative of life during future Mars missions, Navarro-González said, that would suggest that "Viking did detect biological activity, and we didn't realize it."
(Correction: Because of a reporting error, a story in Monday's Health/Science section about the possibility of life on Mars incorrectly described NASA's 1976 Viking mission as the first successful landing on another planet. Viking 1 and 2 were the first spacecraft to land on Mars, but three Soviet landers had previously reached Venus.)
