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 surface imaging to find appropriate 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 at -1.5 km elevation). Viking 2 followed on September 9, 1975 and Lander 2 touched down at Utopia Planitia (47.97° N, 225.74° W, -3 km) 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 seismology. Lander 2 ended communications on April 11, 1980, while Lander 1 lasted until November 13, 1982, Martian day 2,245. Meteorology Science Team Member and UW Atmospheric Sciences Professor Jim Tillman, and his Viking Computer Facility staff, replicated JPL's Mission Operations computer resources thereby providing Lander engineering data for JPL Operations staff thereby extending the mission from approximately sol (Mars day) 1,000 to 2,245.
The Viking results gave the most comprehensive view of Mars to date of any single mission. Volcano's, 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 near the equator. The surface material is mainly iron-rich clay. Measured atmospheric temperatures at the landing sites ranged from -123° Celsius to -23° C, with a variation over a given day of 6 to 50° C. Great seasonal dust storms, pressure changes, and transport of atmospheric gases between the polar caps were observed. Consensus conclusions are the biology experiment produced no evidence of life at either landing site.
The image and components of the above draw from "Viking Mission to Mars" by Dr. David R. Williams, NASA Goddard Space Flight Center, dwilliam@nssdc.gsfc.nasa.gov.