Eruption of a volcano on Io. Composite image made by the Voyager 1 spacecraft showing a volcanic plume on Io, one of the moons of Jupiter. The plume is the semicircular blue, green and red feature extending above the moon's limb at centre left. The plume is about 400km in diameter and about 200km high. Loki is thought to belong to a class of volcanoes with very long eruptive periods, and is the most thermally active area of Io. This image is a combination of frames taken through blue, violet and ultraviolet filters, and was taken on 5 March 1979.