In July 1976, the Viking 1 probe touched down on Mars and failed to find traces of life - but now, three decades later, scientists think the experiment was flawed.
VIking 1 did find evidence of extraterrestrial microbes in soil samples from the Red Planet.
Mathematical analysis of the samples concluded that salts in the soil on Mars 'threw off' initial estimates - and that the soil samples show strong evidence of microbial life.
The new analysis looked for 'complexity' in the samples - an indication of life. To the surprise of the scientists, they found it.
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