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∆ Ancient craters cover most of Mercury, making it look much like the Moon. This image is a mosaic of hundreds of separate smaller pictures taken by the space probe Mariner 10 .

∆ With a diameter of 3,000 miles (4878 km),Mercury is much smaller than the Earth and only a little bigger than the Moon.

Terrific temperatures The long days and nights make Mercury at the same time scorching hot and freezing cold. During the day, the Sun blazes down relentlessly, baking the surface to temperatures up to about 842°F (450°C). That is hot enough to melt the metals lead, tin and zinc. When the Sun goes down and night falls, temperatures plunge rapidly. By the end of the long night, the dark surface of Mercury is a deep-frozen -292°F (–180°C). On Earth, this would be nearly cold enough to turn the air that we breathe into liquid.

Mercury ’ s long days All planets spin around in space like a top as they travel in orbit around the Sun. The Earth spins around once a day. The other planets spin around in different periods of time. Mercury spins round very slowly. It takes nearly 59 days to spin around once. This slow spin gives Mercury a very long “day,” or time between sunrise and sunset. Its “day” lasts 88 Earth-days. Its “night” is also 88 Earth-days long.

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