Mercury is the nearest planet to the sun, orbiting at an average distance of about 58 million kilometers. Because Mercury is the closest planet to the sun, it moves the faster than any other planet in our solar system travelling at an average speed of nearly 48kms. per second and completing an orbit in just under 88 days. Mercury is very small and rocky. Most of the surface has been heavily cratered by the impact of meteorites, although there are also smooth, sparsely cratered plains.

The Caloris Basin is the largest crater, measuring about 1300kms. across. It is thought to have been formed when an asteroid sized rock hit the planet, and is surrounded by concentric rings of mountains thrown up by the impact. The surface also has many ridges that are thought to have been formed when the hot core of the young planet cooled and shrank about four billion years ago, buckling the planet's surface in the process. The planet rotates about its axis very slowly, taking nearly 59 Earth days to complete one rotation. As a result, a solar day on mercury is about 176 Earth days- twice as long as the 88- day Mercurian year.

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