... Credit: Galileo Project , JPL , NASA Explanation: Two sulfurous eruptions are visible on Jupiter's volcanic moon Io in this color composite Galileo image . On the left, over Io's limb, a new bluish plume rises about 86 miles above the surface of a volcanic caldera known as Pillan Patera. In the middle of the image, near the night/day shadow line, the ring shaped Prometheus plume is seen rising 45 miles above Io while casting a shadow to the right of the volcanic vent. ... New Horizons at Io . ...