The Viking 1 lander which arrived on Mars in July 1976: Scientists now believe there is strong evidence of microbial life in the soil samples analysed by Viking 1
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.
'This suggests a robust biological response,' say the researchers, from the University of Siena and California's Keck Institute. Read More