This is an image of Io.
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Evolution of Io
Io is the smallest of the major Galilean satellites, with a size that could be that of the rocky core of one of the other Galilean moons. Io is heated through the process of tidal forcing, which causes the moon to be volcanic. Since the density indicates that the composition
of Io is mostly rocky, there is the possibility that Io started out similar in character to the other icy moons and lost it's icy mantle over time due to tidal forcing.
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