The Viking mission was the first to explore Mars' surface. Two spacecraft, Viking 1 and 2, each with an orbiter and a lander, made the journey to Mars. The landers touched down on Mars' red sand in 1976. They took pictures, studied the surface and atmosphere, and looked for life, while the orbiters gathered data and mapped the entire planet's surface.

Purpose: to study the geology and atmosphere of Mars and look for signs of life
Spacecrafts: Viking 1 and 2, identical orbiters and landers
Lander touchdowns: Viking 1, July 20, 1976; Viking 2, September 3, 1976
Conclusions: found no clear evidence of life
Significance: the first successful landing of an Earth spacecraft on Mars

Image credits: courtesy NASA.