Mercury is a heavily cratered planet. Its surface is similar to the surface of our Moon. Cratering on Mercury triggered volcanic eruptions that filled much of the surrounding area. The largest crater on Mercury is the Caloris Basin which is 800 miles (1,300 km) across. It may have been formed by as asteroid hitting Mercury. Many of the craters on Mercury have been named for writers, musicians, painters, and other artists.
There are also areas of relatively flat planes on Mercury; these are called planitas.
Lines of mountainous cliffs, rupes, scar the surface of Mercury. These long lines were probably formed when the planet cooled about 4 billion years ago, causing these lon cracks to form.