When the two Viking landers set down in the summer of 1976, we held our breaths, waiting to hear if these spacecraft would find signs of life on Mars. The two landers were identical and carried identical equipment. Both performed the Labeled Release Experiment, designed to detect life in soil samples scooped up from Mars’ surface. But the results were inconclusive, and, although some scientists tried for a year or so afterwards to find a biological explanation to prove that there was life on Mars, the ultimate consensus was that, no, the Viking landers did not find Martian life. This week, though, an international team of mathematicians and scientists reach a different conclusion in a paper published in the International Journal of Aeronautical and Space Sciences. These scientists – who studied the mathematical complexity of the Viking results – say the Vikings did find life on Mars 36 years ago.

What does mathematical complexity have to do with Martian life? Remember that, in mathematical representations of the world, a living system (like a microbe) is more complicated than a system that is purely physical (like a rock).

The Viking landers didn’t worry about mathematical complexity in this way. They were designed to use their robotic arms to scoop up soil samples and study the Martian soil with three separate experiments. The Labeled Release Experiment had the most interesting result, because it appeared to show signs of microbial metabolism in the soil. In other words, researchers at first thought they had found signs of the process by which a living microbe gets its energy and nutrients. That finding caused a flurry of excitement! Meanwhile, however, the other two Viking experiments failed to reveal organic molecules – molecules containing carbon – in the Martian soil. And organic molecules are necessary for life as we know it.

Ultimately, scientists became convinced that the positive results from the Labeled Release Experiment were likely caused by chemical reactions – not biological ones – from highly oxidizing soil conditions. Iron oxide in Mars’ soil is what gives Mars its red color, after all, so this explanation made sense to all, back in 1976 and 1977 when these experiments were being discussed in journals and at meetings of space scientists.

Fast forward 36 years to our time, and to a team of researchers led by Giorgio Bianciardi of the University of Siena. These researchers took a different approach to analyzing the Vikings’ results. They obtained hard copies – actual print outs – of Viking data from the original researchers. They then distilled the Viking Labeled Release data into sets of numbers and analyzed the results from a numerical perspective, looking for the mathematical complexity that is the signature of life.

And, according to these researchers in their paper in the International Journal of Aeronautical and Space Sciences, they found it. They say they found close correlations between the Viking experiment results’ complexity and those of biological data sets from earthly life, adding:

This suggests a robust biological response.

Other researchers do not agree, of course, which is why no one is shouting “life on Mars!” from the rooftops. Critics say these researchers’ method has not been proven to be able to differentiate between living systems and systems that are purely physical, even here on Earth.

Yet it is intriguing to hear a different interpretation of the results of the 1976 Viking Labeled Release Experiment after so many years. Perhaps it will lead to new experiments to be conducted on Mars, and new results, in the search for life on this neighboring world.

Bottom line: An international team of researchers has taken a numerical approach to analyzing results of the Viking landers Labeled Release Experiment from 1976. They say the Viking experiment from 36 years ago did show the existence of life on Mars.