Mars exploration. Artwork showing the orbits of the space probes Mariner 9 (blue track) and Viking I (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 I was launched on August 20th 1975 and on June 19th 1976 was put in a temporary orbit (dashed purple line) which was then lowered to the final orbit (solid purple line). Viking I and its twin probe (Viking II) collected about 52,000 images of Mars. Each Viking also had a lander unit which relayed back information of the Martian surface.