This old photograph, taken by Mariner 10 in 1974, clearly shows Mercury's broken and crater-filled surface. The deep pits, seen in many parts of the planet in the image, are where meteorites, comets and asteroids travelling through space have collected.

Some craters are characterised by lines radiating out from their edges like a rounded gap. These "crater streams" are formed when Mercury was struck so violently that it broke apart, ejecting the soil contained in the impact far away. As this dust and rubble falls to the ground in straight lines, a distinctive scar forms around the perimeter of the pit.

These craters and traces of Mercury have been named by various authors, one of them being the famous children's book author Dr Seuss. This nomenclature, as well as the global changes of the planet's regions, stimulate the imagination.

Image description:

This binary image scan of Mercury's hemisphere, taken against a black space background, darkens as it moves towards the centre of the planet, while its outer edges are illuminated. The surface is covered in different shades of grey and blotches, dotted with craters of all kinds. In particular, a crater in the centre of the planet stands out, surrounded by white and striated crater rays.

This binary scan of a hemisphere of Mercury, presented against a black space background, gradually darkens towards the centre of the planet, while the edges are brightened. The surface is covered in varying shades of grey and blotches, with craters of all sizes. In particular, a crater in the centre of the planet is particularly prominent, surrounded by striated crater rays.

This dual-image scan of one hemisphere of Mercury against black space is shaded towards the centre of the planet and the outer edges are illuminated. The surface is covered with craters of all kinds, with various shades of grey and blotches. In particular, a crater in the centre of the planet leaves a white trail surrounded by striped crater rays.