Did the Viking missions discover life on Mars 50 years ago? These scientists think so.

NASA's Viking missions to Mars may have discovered evidence for life on the Red Planet after all, according to scientists who are seeking to correct what they believe to be a 50-year-old mistake that has led everybody to think that Mars is lifeless.

Viking 1 and Viking 2 landed on Mars in 1976. On board they carried three life-detection experiments, which produced positive results. But the apparent failure of another instrument, the Gas Chromatograph-Mass Spectrometer (GC-MS), to detect organic molecules necessary for life led Viking Project Scientist Gerald Soffen to conclude, "No bodies, no life."

However, scientists led by Steve Benner, a professor of chemistry at the Foundation for Applied Molecular Evolution in Florida, now argue that the Viking data shows something quite different to what the textbooks say.

"The GC-MS showed an absence of organic molecules, or at least that was the [Viking team's] interpretation," Benner told Space.com. "The problem is that we now know that it did find organic molecules!"

The GC-MS worked by heating samples of Martian dirt — first to 120 degrees Celsius (248 degrees Fahrenheit) to remove any excess carbon dioxide from Mars' atmosphere, and then to 630 degrees C (1,166 degrees F) in order to vaporize any organics present in the dirt so that they could be analyzed by the mass spectrometer.

Puzzlingly, all that the mass spectrometer detected was an unexpected second burst of carbon dioxide and a small quantity of methyl chloride and methylene chloride, when instead there should have been some organic molecules present, if only from meteoritic debris that had built up over billions of years. For there to be none at all, argued the Viking team, required an unknown oxidant. Meanwhile, the carbon dioxide was assumed to have been left over from being observed by the container holding the sample, while methyl chloride was thought to be terrestrial contamination from cleaning solvents originating from the clean room on Earth where the instrument was assembled. This conclusion was bolstered by the fact that, during in-flight tests on the way to Mars, freons such as chlorofluorocarbons that had come from the clean room had been detected.

The problem with that interpretation, according to Benner, is that "methyl chloride is not a cleaning solvent — it's a gas that boils at minus 24 degrees Celsius [minus 191 F]."

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