Multiple image of the Martian surface and Viking Lander, 1976.
© National Aeronautics & Space Administration / Science & Society
This shows many images of the colour scale on the lander, used to calibrate the pictures, against the Martian surface. 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.