|This image acquired by the Galileo spacecraft shows two volcanic plumes on Jupiter's moon Io. One plume was captured on the bright limb or edge of the moon, erupting over a caldera (volcanic depression) named Pillan Patera. The second plume, seen near the terminator, the boundary between day and night, is called Prometheus. The shadow of the airborne plume can be seen extending to the right of the eruption vent. (The vent is near the center of the bright and dark rings).