Goals: NASA's Viking mission to Mars was composed of two pairs of spacecraft -- Viking 1 and Viking 2 -- each consisting of an orbiter and a lander. The spacecraft were designed to take high-resolution images of the Martian surface, characterize the structure and composition of the atmosphere and surface, and search for evidence of life.

Accomplishments: Viking 2 lander set down on Utopia Planitia and operated until April 1980. The four Viking spacecraft provided numerous new insights into the nature and history of Mars, producing a vivid overall picture of a cold weathered surface with reddish volcanic soil under a thin, dry carbon dioxide atmosphere, clear evidence for the existence of ancient river beds and vast floods, and no detectable seismic activity.

Although no traces of life were found, Viking found all elements essential to life on Earth -- carbon, nitrogen, hydrogen, oxygen and phosphorus -- were present on Mars.