Scientists believe they've found evidence for life on Mars - in data collected 36 years ago.
A new analysis of results from experiments carried out by the 1976 Viking mission to Mars indicates the presence of microbes in the Martian soil.
In three experiments carried out by the two Viking probes, a cocktail of nutrients was added to Martian soil, in the hope that any microbes present would consume the nutrients and release CO2 or methane.
But when one of the experiements appeared to show positive results by producing CO2, the scientists concluded that the cause was probably an oxidizing agent within the soil, as the other experiments failed to find ant organic molecules in the soil.
Now, though, those results have been re-examined with an emphasis on the mathematical complexity of the data. You'd expect more complexity from samples containing biological life than from inert ones - and this is exactly what the scientists found.
And, says the team, the active experiments clearly sorted with terrestrial biological data series whereas the Viking LR control data sorted with known terrestrial non-biological data.
"To paraphrase an old saying, if it looks like a microbe and acts like a microbe, then it probably is a microbe,” says Joseph D. Miller, associate professor of cell and neurobiology at the Keck School of Medicine, University of Southern California.
"The presence of circadian rhythmicity and a high degree of mathematical complexity or order in the LR data most likely means Viking discovered microbial life on Mars over 35 years ago."
Miller stresses that the new analysis is by no means conclusive proof - and calls for specific experiments to be carried out on Mars with the aim of detecting life.
"A smoking gun would be taking a picture under a microscope of Mars bacteria," he says.
"But the case is getting stronger. We know there is sub-surface water ice, and perhaps liquid water in regions that seem to release methane gas into the atmosphere. Water is necessary for life and methane is a potential signature of biology."
Complexity Analysis of the Viking Labeled Release Experiments is available here.