Photo courtesy of NASA

by Cody Whiteway and Jonathan Woodliffe

Mercury is the planet closest to the Sun. As Mercury rotates slowly on its axis about once every 59 Earth days, it moves in an elliptical or oval-shaped orbit around the Sun, faster than any other planet. A day on Mercury is 58.65 Earth days, a rotation slower than that of any other planet, except Venus. However, Mercury`s year is equal to 87.97 Earth days; it goes around the Sun about once every 88 days, moving about 48 km per second.

Mercury is very close to the Sun, about 46 million km from the Sun at its closest point, and about 69.2 million km at its farthest point. Mercury is about 91.7 million km from the Earth at its closest point. The diamater of Mercury is 4,880 km; the size of Mercury is smaller than any other planet's, except Pluto's. Mercury is only about one-third the size of the Earth. Mercury 's gravity is 38% that of Earth's, approximately a third as strong as that of the Earth. A 100 pound person would only weigh a third of that, or 38 pounds on the surface on Mercury.

Mercury has no greenhouse effect because there is no atmosphere to speak of to trap the heat from the Sun. Mercury's atmosphere is very thin and is made of very small amounts of sodium and helium. Mercury's sky is black, and stars can likely be seen during the day because of the lack of atmosphere. Mercury does not have enough gases in its atmosphere to reduce the amount of heat and light it receives from the Sun. Mercury is dry and extremely hot; the Sun's rays are about 7 times as strong on Mercury as they are on Earth. The temperature of Mercury's surface, on the side of Mercury closest to the Sun, rises to over 400 degrees Celsius during the day. But at night, on the side facing away from the Sun, the temperature drops as low as -193 degrees Celsius.

Mercury is called the small rocky planet. It has a large core or center of liquid iron about 1800 to 1900 km wide in diameter. The outer shell is only 500 to 600 km thick. A magnetic field surrounds Mercury, though it is not as strong as the field around the Earth. Astronomers believe that Mercury's magnetic field is because of its iron-bearing core.

Bibliography and Additional Sources of Information

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