Phobos, one of the moons of Mars, 1976.
© National Aeronautics & Space Administration / Science & Society
Photographed by one of the Viking Orbiters. Mars has two small irregularly shaped moons, Phobos, some 22 kilometres acros, and Deimos which is even smaller. Both moons are bare and rocky and are pitted with impact craters. The composition of the moons is similar to that of bodies from the asteroid belt between Mars and Jupiter, suggesting that Phobos and Deimos are captured asteroids which have settled into orbit around Mars. Two Viking spacecraft were launched towards Mars by NASA in 1975, each carrying a lander spacecraft and an orbiter. Both succesfully landed their probes on Mars to study the Martian environment, soil constituents and to search for simple life forms.