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This picture of Io, the innermost Galilean satellite, was taken by Voyager 1 on the morning of March 5, 1979 at a range of 377,000 kilometers (226,200 miles). The smallest features visible are about 10 kilometers (6 miles) across.
The reddish, white and black areas are probably surface deposits, possibly consisting of mixtures of salts, sulfur and sublimate deposits of possible volcanic origin. Many of the black spots in these pictures are associated with craters of possible volcanic origin. The lack of impact craters on Io suggests that the surface is relatively young compared to the other Galilean satellites and some of the terrestrial planets such as Mercury and the Moon.
The Voyager Project is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif.