Mars appears red because iron oxide dust covers much of the rocky surface.

The longer version

Iron in Martian dust behaves much like rust on Earth. Minerals containing iron reacted with oxygen long ago, producing reddish oxides that spread across the surface as fine grains. Grains coat rocks, slopes and plains alike. Winds lift this dust into the atmosphere and carry it worldwide, tinting the sky a pale butterscotch shade.

The color is only skin deep. Beneath the dust, much of the terrain is dark volcanic rock, and polar caps of water and carbon dioxide ice sit at the poles. Because the grains are so fine, dust storms can envelop the whole planet and take weeks to settle.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.