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Mercury is the closest planet to the Sun and is the smallest of the 8 planets that orbit the Sun. Because Mercury is so relatively close to the Sun, its surface temperature can reach about 800° (F) (430° Celsius), but because Mercury doesn’t have an atmosphere, it doesn’t retain heat and, consequently, nighttime temperatures can plummet down to -280 Fahrenheit (-170 degrees Celsius). It is believed the planet was named after the Roman deity, Mercury (the messenger to the gods), because it orbits the Sun every 116 days and, therefore, appears to move very quickly across the heavens.

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