Martian moon Phobos. This is the first image of the moon captured by the Viking 1 spacecraft on 25th July 1976.Phobos is the larger and innermost of the two Martian moons. An irregular shape, it measures 19 by 21 by 27 kilometres, and orbits some 6000 kilometres above the Martian surface, taking 7.6 hours to complete an orbit. Stickney Crater (top) is 10 kilometres across. Viking 1 was launched on 20 August 1975 and on 19 June 1976 entered orbit around Mars. 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.