NASA's Viking Mission to Mars was composed of two spacecraft, Viking 1 and Viking 2, each consisting of an orbiter and a lander. The primary mission objectives were to obtain high resolution images of the Martian surface, characterize the structure and composition of the atmosphere and surface, and search for evidence of life. Viking 1 was launched on August 20, 1975 and arrived at Mars on June 19, 1976. The first month of orbit was devoted to imaging the surface to find appropriate landing sites for the Viking Landers. On July 20, 1976 the Viking 1 Lander separated from the Orbiter and touched down at Chryse Planitia (22.48° N, 49.97° W planetographic, 1.5 km below the datum (6.1 mbar) elevation). Viking 2 was launched September 9, 1975 and Lander touched down at Utopia Planitia (47.97° N, 225.74° W, 3 km below the datum elevation) on September 3, 1976. The Orbiters imaged the entire surface of Mars at a resolution of 150 to 300 meters, and selected areas at 8 meters. The Viking Landers transmitted images of the surface, took surface samples and analyzed them for composition and signs of life, studied atmospheric composition and meteorology, and deployed seismometers. 2 Lander ended communications on April 11, 1980, while Lander 1 lasted until November 13, 1982, sol 2,245. (A sol is a Mars day of 24.66 hours.) Lander 1 was scheduled to be shut down after the first year (669 sols) but through the efforts of Meteorology Science Team Member, Atmospheric Sciences Professor Jim Tillman, the project agreed to continue the mission until NASA Jet Propulsion Laboratory, shut down its computer facility that handled all spacecraft data and provided engineering results for the Mission Operations staff. To enable continued Mission Operations, Tillman and his staff, enhanced his Viking Computer Facility to replicate Mission Operations processing from raw binary spacecraft bits to finished Meteorology and Engineering data, the later enabling continued Lander engineering analyses and operation from approximately sol 1,000 through 2,245.

The results from the Viking experiments gave the first, and still the most comprehensive view of Mars to date of any single mission. Volcanoes, lava plains, immense canyons, cratered areas, wind-formed features, and evidence of surface water are apparent in the Orbiter images. The planet is divided into two main regions, northern low plains and southern cratered highlands. Superimposed on these regions are the Tharsis and Elysium bulges, which are high-standing volcanic areas, and Valles Marineris, a system of giant canyons approximately 5,000 km (3,000 miles) long, near the equator. The surface material at both landing sites can best be characterized as iron-rich clay. Measured temperatures at the landing sites ranged from 150 to 250 K, with a variation over a given day of 35 to 50 K. Great seasonal dust storms, pressure changes, and transport of atmospheric gases between the polar caps were observed. The biology experiment produced no evidence of life at either landing site.