The new analysis centres on one of the three experiments carried by the probe: the Labeled Release (LR) experiment. This instrument searched for signs of life by mixing samples of Martian soil with droplets of water containing nutrients and radioactive carbon. If the soil contained microbes, the reasoning went, they would metabolise these carbon atoms and nutrients and release either methane gas or radioactive carbon dioxide, either of which would tip off the probes that life existed in the soil.

That's exactly what happened. But other experiments aboard Viking didn't back up the LR, and NASA scientists had to dismiss the LR's findings as anomalous.

But now an analysis by a University of Southern California neurobiologist (and former NASA space shuttle project director) and a mathematician from Italy's University of Siena could reverse that thinking. They used a technique called cluster analysis, which clusters together similar-looking data sets, to see what would happen. They found the analysis created two clusters: one for the two active experiments on Viking and the other for five control experiments.

Further, when they compared Viking's data to confirmed biological sources on Earth, like temperature readings from a lab rat, the analysis correctly clustered the biological readings with the active Viking experiment data, separate from the non-biological data in the control experiments. All that essentially means that the cluster analysis, when fed a good deal of data from both biological and non-biological sources, correctly separates the two types of data. And when it does so, it lumps the Viking data into the "biological" category.

That's not concrete evidence for microbial life on Mars. It's merely concrete evidence that there is a stark difference between Viking's LR experiment data and the control experiment data. And it's evidence that the Viking data tracks with biological rather than non-biological data. More study is necessary (isn't it always?), but if the cluster analysis is to be believed then our first shot at detecting microbial life in the soils of Mars may have hit pay dirt - and we didn't even realise it.

[NatGeo]