The Viking program consisted of a pair of identical NASA space probes, Viking 1 and Viking 2, which arrived on Mars in 1976. Each spacecraft was composed of two main parts: an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface. The orbiters also served as communication relays for the landers once they touched down. Viking 1 lasted from 1975-1982, while Viking 2 lasted from 1975-1980
The launch of Viking 1 on a Titan 3E/Centaur rocket, 1975-Aug-20
The Viking program's two landing sites, Chryse Planitia (Viking 1, left) and Utopia Planitia (Viking 2, right), 1976
Phobos (left) and Deimos (right) imaged by the Viking orbiters, 1977-1978
Global mosaic of Mars taken by the Viking 1 orbiter at an altitude of 2,500 km, 1980-Feb-22
Dr. Carl Sagan beside the mockup of a Viking lander in Death Valley, California sometime in 1980
Viking 1 (left) and Viking 2 (right) landers spotted by the Mars Reconnaissance Orbiter in December 2006