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Mars, the fourth planet from the Sun, is more like Earth than any other body in our solar system. It has mountains and valleys, polar ice caps, and dry riverbeds. It has seasons, an atmosphere with clouds, winds and dust storms, and a solid rocky surface. But Mars is only half as large as our planet. Its thin atmosphere is 95 percent carbon dioxide. And it's a very cold place--in winter it often falls to minus 118ºC (minus 180ºF). No liquid water exists there today, but Mars' many dry riverbeds, both large and small, prove that water once flowed on its surface. |
