False-colour version of a Mariner 10 photograph of the surface of Mercury, the innermost planet, showing its heavily cratered surface. Mariner 10 was the first spaceprobe to visit the planet, making three separate encounters during 1974-5. This image is a mosaic constructed from photographs taken as the spacecraft left the planet after its first fly-by on March 29, 1974. Various shades of blue colouring