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Today it's a very dry, very cold place, but Mars once may have had lakes and seas of water. Ancient features seeming to resemble islands, sandbars and shorelines on Earth can be seen in photos of Martian terrain taken from 1976 to 1981 by the Viking spacecraft in orbit around the Red Planet.

Mars, the Red Planet, the fourth planet from the Sun is named for the Roman god of war. Seen as a red dot in Earth's night sky, it is 1.5 times farther from the Sun than the Earth is. The globe of Mars is only half as large as the Earth.

Mars is more like Earth than any other planet. Its period of rotation and the inclination of its axis are similar. Its density indicates it's made of rocky materials, although with less iron and more lightweight elements and volatiles than the Earth. Its atmosphere is thin enough to allow us to see the surface.

• Mars is the seventh largest planet with a diameter only about one-half that of Earth.
• The fourth planet from the Sun, Mars is about half again as far from the Sun as Earth is.
• Mars thin atmosphere is mostly carbon dioxide.
• Mars clouds and haze are blue, while its surface is red.
• Mars surface has craters, hills, valleys, ridges and plateaus.
• Eons ago, liquid water flowed on the now-eroded martian surface.
• The water left on Mars is frozen in the polar ice caps.
• Mars has two moons.
• Mars is 141,600,000 miles from the Sun.
• The diameter of Mars is 4,222 miles.

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Solar System:	The Sun
Inner System:	Mercury	Venus	Earth	Mars
Outer System:	Jupiter	Saturn	Uranus	Neptune	Pluto
Other Bodies:	Moons	Rings	Asteroids	Comets

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