Viking Mission May Have Missed Mars Life, Study Finds National Geographic News

If future missions are to set the record straight, the study’s authors add, scientists may need to change the ways in which they search. NASA’s Viking Mission to Mars put two landers on the red planet in 1976. Their experiments uncovered mysterious chemical activity in the Martian soil but no clear evidence of life.
Now scientists suggest that telltale signs of life could have been there all along, but Viking’s testing methods were not robust enough to recognize them.