Polar ice cap on Mars, 1976.
© National Aeronautics & Space Administration / Science & Society
Taken from a Viking Orbiter, this shows one of the Martian ice caps, made up of frozen water and carbon dioxide. Two Viking spacecraft were launched towards Mars 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 - none were found.