The Viking Missions:

 Viking 1 and 2 were designed after the Mariner spacecraft. This design can be seen in the photo above. They consisted of an orbiter and lander. The orbiter weighed 900 kg and the lander 600 kg. Both landers contained experiments to search for Martian micro-organisms. Approximately 75 percent of what we know about Mars, we learned from the two Viking missions.

 Viking 1 :

Viking 1 went into orbit about Mars on June 19, 1976. The lander touched down on July 20, 1976, on the western slopes of Chryse Planitia. The results of these experiments are still being debated. The lander provided detailed color panoramic views of the Martian terrain. It also monitored the Martian weather. Viking 1 lander was accidentally shut down on November 13, 1982, and communication was never regained. The Viking 1 Lander took over 2,450 photos.

 Viking 2:

Viking 2 went into orbit about Mars on July 24, 1976. The lander touched down on August 7, 1976 at Utopia Planitia. The results of these experiments are still being debated. The lander provided detailed color panoramic views of the Martian terrain. Overall 2,170 photo's of the surface were taken. It also monitored the Martian weather. Viking 2 lander used Viking 1 orbiter as a communications relay and had to be shut down at the same time as the orbiter on August 7, 1980.

 Mars Pathfinder: