Mariner 9 and Viking 1 orbiting Mars, illustration. Trajectories and orbits of the space probes Mariner 9 (blue track) and Viking 1 (purple) around Mars (centre right). Mariner 9 was launched in May 1971; it collected more than 7000 images which enabled the mapping of most of the Martian surface; it also imaged the two moons of Mars, Deimos and Phobos (red tracks). Viking 1 was launched on 20 August 1975 and on 19 June 1976 was put in a temporary orbit (dashed purple line) which was then lowered to the final orbit (solid purple line). Viking 1 and its twin probe (Viking 2) collected about 52,000 images of Mars. Each Viking also had a lander unit which relayed back information from the Martian surface.