Decades after analysis of data from soil samples obtained by NASA's Viking probes concluded there was no life on Mars, new analysis has led to conclusion that the first analysis was flawed and that the probes actually found evidence of life on Mars.
The two 1976 NASA space probes, Viking 1 and Viking 2, had brought back photographs and conducted three experiments on Mar's air and soil samples. The experiments looked for evidence of life on Mars. Only one of the experiments called the Label Release experiment found evidence suggestive of life. The Label Release tests found signs of CO2, a gas produced by all living organisms in the soil. But scientists ignored the evidence from this experiment and concluded that though there were signs of geological activity, there were no signs of biological activity on Mars.
The latest analysis by Miller et al., took a different approach based on the idea that biological processes, being more complex than known non-biological process, are associated with greater complexity.
Analysis for complexity yielded results showing correlations between terrestrial data sets and data sets from Viking soil samples. According to the scientists, the high degree of order and complexity their analysis detected is characteristic of biological processes.
The study abstract, said: "We have applied complexity analysis to the Viking LR data. Measures of mathematical complexity permit deep analysis of data structure along continua including signal vs. noise, entropy vs.negentropy, periodicity vs. aperiodicity, order vs. disorder etc....Martian LR active response data cluster with known biological time series while the control data cluster with purely physical measures."
The study continued: "The complexity pattern seen in active experiments strongly suggests biology while the different pattern in the control responses is more likely to be non-biological." The abstract concluded: "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. This suggests a robust biological response. These analyses support the interpretation that the Viking LR experiment did detect extant microbial life on Mars."
The key word in the conclusion is "extant," implying that when Viking 1 and Viking 2 landed on Mars in 1976, there was microbial life on the planet.
Daily Mail reports that reassessment of the evidence was prompted by discovery of substances called "perchlorates" in the soil at the site where the Mars Lander, Phoenix, touched down in 2008. Scientists had earlier assumed contamination when they detected perchlorates in the Viking samples.
But just how conclusive do scientists agree the evidence is?
Critics say the mathematical analytical technique employed has not yet been used successfully used on Earth for distinguishing biological from non-biological processes, so it is too early to draw firm conclusions.
Planetary scientist and astrobiologist at NASA's Ames Research Center in Moffet Field, Calif., Christopher McKay, said: "Ideally to use a technique on data from Mars one would want to show that the technique has been well calibrated and well established on Earth. The need to do so is clear; on Mars we have no way to test the method, while on Earth we can."
Mckay, in an interview with Discovery News, expressed guarded skepticism: "Finding organics is not evidence of life or evidence of past life. It's just evidence for organics."
Discovery News reports that the lead author, neuropharmacologist and biologist Joseph Miller at the University of Southern California Keck School of Medicine, said NASA does not need to send a human expedition to Mars to prove the claim: "The ultimate proof is to take a video of a Martian bacteria. They should send a microscope — watch the bacteria move."
He said: "On the basis of what we've done so far, I'd say I'm 99 percent sure there's life there.'"