Forty years ago, two landers in a Martian experiment known as the Viking Labeled Release produced positive evidence for microbial life on the red planet.
Separated by 4,000 miles, both of the Viking landers yielded similar, repeatable results, prompting researchers to conclude – controversially – that Martian life had been detected.
Though many have dismissed the findings as non-biological, the soil materials that would support this explanation have yet to be identified.
With the historical data considered, along with recent evidence of water, complex organic molecules, and methane on Mars, astrobiologists are now warning against ruling out the possibility of life, and instead argue that the evidence shows it ‘must be considered.’
In an article published to the journal Astrobiology, experts from Arizona State University, Tempe, and the National Institutes of Health, Bethesda say the evidence is ‘consistent with a biological explanation,’ suggesting microorganisms on Mars adapted and evolved to meet harsh environmental conditions.
The researchers delved into the findings from the 1976 Viking Labeled Release (LR) experiment, and evaluated the ‘non-biological hypotheses.’
In the LR experiments, samples of Martian soil from both landers were subjected to nutrient injection, preheating, and were even stored in the dark for roughly two months.
The results showed striking similarities to responses seen in terrestrial soil, including data from samples collected in California, Alaska, and Antarctica.
‘Each of these characteristics is reminiscent of responses by a compendium of terrestrial microorganism species, including the initial positive responses, the 160C and 50C heat controls, the reabsorption of evolved gas upon second injection of nutrient, and death from isolated long-term storage,’ the authors note.
Numerous explanations have been proposed over the years to address these findings, including those which have suggested that the results were ‘most likely caused by a non-biological soil oxidant.’
But, no such oxidant that could satisfy all of the findings has ever been identified, and there have been no further metabolic experiments on the red planet.
As manned missions to Mars are now ‘inevitable’ in the years to come, the researchers say it is a concern for health, safety, and biology to explain the results found in 1976.
‘Plans for any Mars sample return mission should also take into account that such a sample may contain viable, even if dormant, alien life,’ the authors write.
And, according to the team, this is the ‘only pristine life-detecting experiment that we will ever have,’ as the Viking landers were heat treated to reduce microbial counts – and no other spacecraft have been since.
Consequently, these untreated craft may have infected the planet with terrestrial ‘hitch-hikers.’
The authors urge future missions to carry out life-seeking experiments, including the search for organic molecules of biological importance.
‘Even if one is not convinced that the Viking LR results give strong evidence for life on Mars, this paper clearly shows that the possibility must be considered,’ says Chris McKay, PhD, Senior Editor of Astrobiology and an astrobiologist with Nasa Ames Research Center.
‘We cannot rule out the biological explanation. This has implications for plans for sample return from Mars and future human missions.’
Source: The Mail