The Viking mission to Mars sent twin spacecraft to the Red Planet. This image shows a model of one of the Viking spacecraft, which were made of two parts: an orbiter and a lander. The orbiter's initial job was to survey the planet for a suitable landing site. Later the orbiter's instruments studied the planet and its atmosphere, while the orbiter acted as a radio relay station for transmitting lander data. Once on the surface of Mars, the lander surveyed the soil, wind, and atmosphere and conducted numerous experiments to determine the existence of past or present life.