Did Viking Found Life on Mars?

NASA's Curiosity rover is set to land on Mars in August and will hunt for signs of life's potential on ancient Mars. Some scientists still believe that the Viking mission has already found evidence of life.

A view of the boulder-strewn field of red rocks reaches to the horizon nearly two miles from Viking 2 on Mars' Utopian Plain. Image credit: NASA

A six-inch-deep trench in the Martian soil dug by Viking 1 in February 1977. The goal was to reach a foot below the surface for sampling. Credit: NASA

The Curiosity rover is currently on its way to Mars, scheduled to make a dramatic landing within Gale Crater in mid-August and begin its hunt for the geologic signatures of a watery, life-friendly past. Solid evidence that large volumes of water existed on Mars at some point would be a major step forward in the search for life on the Red Planet.

But has it already been found? Some scientists say yes.

Researchers from universities in Los Angeles, California, Tempe, Arizona and Siena, Italy have published a paper in the International Journal of Aeronautical and Space Sciences (IJASS) citing the results of their work with data obtained by NASA's Viking mission.

The twin Viking 1 and 2 landers, which launched in August and September of 1975, successfully landed on Mars in July and September of the following year. Their principal mission was to search for life, which they did by digging into the ruddy Martian soil looking for signs of biological activity.

The Viking Labeled Release experiment added nutrient to samples of Mars soil, and then checked to see if microbes that may have been living in the soil expelled any waste products. Gas was released, but scientists could not rule out that this could have been the result of abiological chemical reactions.

Now, 35 years later, one team of researchers claims that the Viking landers did indeed detect life within their soil samples. Their study looked at the time series of what happened between the moment of adding nutrient and the release of gas, and said it was similar to what happens when microbes living in soil on Earth take up nutrients and exhale waste.

"Active soils exhibited rapid, substantial gas release," the team's report states. "The gas was probably CO₂ and, possibly, other radiocarbon-containing gases."

By applying mathematical tools from the field of complexity analysis to the Viking data, the researchers found that the martian samples behaved differently than a non-biological control group. 

"Control responses that exhibit relatively low initial order rapidly devolve into near-random noise, while the active experiments exhibit higher initial order which decays only slowly," the paper states. "This suggests a robust biological response."

However, a process of conclusively identifying life has not yet been perfected - not even here on Earth.

“It’s an interesting and novel approach, but I don’t think it’s necessarily the definitive proof of life that they are claiming,” says Michael New, Astrobiology Discipline Scientist at NASA. “Are there abiological processes that could also produce that same sort of signal?”

New says just because the pattern seen in the results resembles life, doesn’t necessarily mean it is life.

"In the absence of a predictive model, it's hard to say that when two series of measurements have the same properties, they are produced by the same phenomenon," he says.

The new study shows that questions about the old Viking data still live on. Future missions, including Curiosity rover, will hopefully help us find some answers about the potential for life on Mars.