Viking's Martian Organics: A New Look at 50-Year-Old Data

The Viking 1 and Viking 2 missions, which landed on Mars in 1976, included three experiments designed to detect life. These experiments yielded positive results. However, another instrument, the Gas Chromatograph-Mass Spectrometer (GC-MS), reportedly did not detect organic molecules, leading project scientists to conclude that Mars was lifeless.

Now, a team of scientists led by Steve Benner, a professor of chemistry at the Foundation for Applied Molecular Evolution, proposes a different interpretation of the Viking data.

"Benner indicates that the GC-MS did detect organic molecules, but through their degradation products."

The Original Viking Puzzle

The GC-MS operated by heating samples of Martian soil, first to 120 degrees Celsius and then to 630 degrees Celsius, to vaporize any organic compounds. The mass spectrometer detected an unexpected release of carbon dioxide along with methyl chloride and methylene chloride.

The original Viking team interpreted the carbon dioxide as residual and the methyl chloride as terrestrial contamination from cleaning solvents, postulating an unknown oxidant was responsible for destroying any organics. This oxidant was also used to explain away the positive results from the other three life-detection experiments.

A New Chemical Clue: Perchlorate

Benner disputes the cleaning solvent interpretation for methyl chloride, noting its gaseous state at relevant temperatures. The resolution to the puzzle, according to Benner, emerged in 2008 when NASA's Phoenix lander discovered perchlorate on Mars.

In 2010, astrobiologist Rafael Navarro-González demonstrated that heating organics in the presence of perchlorate produces methyl chloride and carbon dioxide. This reaction yields approximately 99% carbon dioxide and 1% methyl chloride, aligning with the GC-MS observations.

Reinterpreting the Data

This reinterpretation suggests that the GC-MS did detect organics, but in a degraded form.

"This finding supports the possibility that the three initial life-detection experiments—the Label Release, Pyrolytic Release, and Gas Exchange experiments—may have indeed found evidence of life, removing the need for a previously hypothesized strong, undiscovered oxidant."

A Model for Martian Life

Benner and colleagues have developed a model, named BARSOOM (Bacterial Autotrophs that Respire with Stored Oxygen On Mars), to describe potential Martian microbes. This model proposes autotrophic bacteria that perform photosynthesis and store oxygen to use when dormant, which could explain oxygen emissions detected by the Gas Exchange experiment.

Benner asserts that the initial misinterpretation of GC-MS results has delayed astrobiological research on Mars for 50 years. He advocates for renewed scientific debate regarding the Viking evidence for life on Mars, particularly as the 50th anniversary of the Viking landings approaches.