Viking 2

Viking 2 landed on Mars in September 1976 -- immediately following the first successful spacecraft landing on Mars by Viking 1 -- and was part of NASA's early two-part mission to investigate the Red Planet and search for signs of life. While neither spacecraft found traces of life, they did find all the elements essential to life on Earth: carbon, nitrogen, hydrogen, oxygen and phosphorus.

Like its predecessor, the Viking 2 mission consisted of a lander and an orbiter designed to take high-resolution images, and study the Martian surface and atmosphere. Both the Viking 1 and 2 landers benefited greatly from their orbiting counterparts, which snapped images that helped mission controllers navigate the landers to safe landing sites.