There are eight planets in our solar system including Earth. So far, no life as we know it exists on any planet other than our own.

Mercury

Mercury, the planet closest to the Sun, has almost no atmosphere, and its dusty surface of craters resembles the Moon. The planet was named for the Roman god Mercury, a winged messenger, and it travels around the Sun faster than any other planet. Mercury is difficult to see from Earth—in fact, the famous astronomer Nicolaus Copernicus, for all his years of research and observation, never once was able to see Mercury.

A photo of a section of Mercury's Shakespeare Quadrangle showing remarkably Moon-like craters. The pictures were taken by the Mariner 10 mission, the only spacecraft to visit Mercury so far. The MESSENGER mission, launched in 2004, entered Mercury's orbit in March 2011.

• Size: Two-fifths the size of Earth in diameter; second smallest in the solar system
• Diameter: 3,032.4 miles (4,880 km)
• Surface: Covered by a dusty layer of minerals (silicates), the surface is made up of plains, cliffs, and craters
• Atmosphere: A thin mixture of helium (95%) and hydrogen
• Temperature: Mercury alternately bakes and freezes, depending on what side is lit by the Sun. The sunlit side can reach up to 950° F (510° C) and the dark side can drop as low as –346° F (–210° C)
• Rotation of its axis: 59 Earth days
• Rotation around the Sun: 88 Earth days
• Your weight: If you weigh 100 pounds on Earth, you would weigh 38 pounds on Mercury.
• Distance from Earth: 57 million miles, at the closest point in its orbit
• Mean Distance from Sun: 36 million miles (57.9 million km)
• Satellites: 0
• Rings: 0

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