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Io, slightly larger than Earth's moon, is the most volcanically active body in the solar system. Deposits of sulphur dioxide frost appear in white and grey hues, yellowish and brownish hues are probably due to other sulphurous materials. Bright red materials, such as the prominent ring surrounding Pele, and black spots mark areas of recent volcanic activity and are usually associated with high temperatures and surface changes.

CREDIT: NASA/JPL/University of Arizona.