The surface of Mercury is heavily cratered due to impacts from meteorites. It also has lines of cliffs which are up to 3 kilometres (km) high and 500 km long. These escarpments may have been formed by the planet's crust wrinkling as the core cooled and contracted billions of years ago. The surface rocks are generally dark and a poor reflector of sunlight. Mercury has about the density as Earth, though it has only about 5% of the volume and mass of our planet. | |
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