Viking 1 leaves for Mars. Courtesy of NASA

The Viking missions to Mars were part of a series of U.S. efforts to explore and better understand the red planet. Each of the two Viking spacecrafts consisted of an orbiter and lander. The landers were sterilized before launch to prevent contamination of Mars with organisms from Earth. Their objectives were to obtain highly detailed pictures of the Martian surface, learn about its composition, and search for life.

Viking 1 was launched on Aug. 20, 1975, followed by Viking 2 on Sep. 9 of the same year. The two orbiters mapped the entire surface of Mars with excellent detail. Each landed safely but found no evidence of life in the soil or atmosphere.

The Viking missions did discover ice on Mars which makes it possible that life existed there many years ago. They also learned a great deal about Martian weather and their close-up images reveal interesting geologic features.

Some of the data returned from these two spacecraft are shown in the image archive below. With this data, scientists began to make educated guesses about what the interior, surface history, and evolution of Mars must be.