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The Romans named Mercury after the messenger of the gods in ancient Rome because Mercury in its motion is the quickest of all the planets. It is also the closest to the Sun, and the smallest with a radius of 2440 km, what is barely larger than the Moon. Its semi-major axis of orbit around the Sun is approximately 58 million km, or approximately 0.4 times the semi-major axis of the Earth's orbit.
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Dimensions of the planets
(credit: JPL/NASA) |
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Mercury has no natural satellite. Being close to the Sun, it is a very hot planet. Moreover, as its atmosphere is almost non-existent it does not heat (no greenhouse effect as on Earth or Venus). The temperature difference between day and night is thus enormous. During the day the temperature reaches 430 °C at the surface, and at night it goes down to -180 °C.
Mercury has a mass of 3.302 × 10 23 kg, or 0.05 times the mass of the Earth. It rotates one day in 58.646 Earth days and its revolution around the Sun takes 87,969 Earth days. It is also animated by a motion called libration . |
