Viking Science

[Astrobiology (Journal)] The Viking missions hosted identical payloads on each of two orbiters and landers. All four missions far exceeded their pre-planned operating times and science objectives, with all but one of the 40 science experiments operating fully successfully.

Viking Press kit

Six experiments on each lander were potentially able to detect evidence of life on the mysterious red planet. Only one such experiment obtained significant positive results, and these were not unequivocal because they could possibly be due to nonbiological chemical reactants in the soil.

However, Mars science was greatly advanced by other measurements. These established contemporaneous environmental conditions as well as evidence for conditions in the geologic past that would have been far more favorable for life than conditions today.

Mars remains the most likely place for life to have originated and evolved other than Earth itself, and it remains the prime target for future exploration.

Further, Mars is the only other body in our solar system (and hence, in the universe) potentially inhabitable by the human species.