From NASA's Planetary Photojournal
This color image, acquired during Galileo's ninth orbit (C9) around Jupiter, shows two volcanic plumes on Io. One plume was captured on the bright limb or edge of the moon, erupting over a caldera (volcanic depression) named Pillan Patera. The plume seen is 140 kilometers (86 miles) high. The second plume, seen near the terminator, the boundary between day and night, is called Prometheus after the Greek god of fire. 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). Plumes on Io have a blue color, so the plume shadow is reddish. The Prometheus plume can be seen in every Galileo image with the appropriate geometry, as well as every such Voyager image acquired in 1979. It is possible that this plume has been continuously active for more than 18 years. In contrast, a plume has never been seen at Pillan Patera prior to the recent images.
Color images from orbit C9 have been merged with a high resolution mosaic of images acquired in various orbits to enhance the surface detail. North is to the top of the picture. The resolution is about 2 kilometers (1.2 miles) per picture element. This composite uses images taken with the green, violet, and near-infrared filters of the Solid State Imaging (CCD) system on NASA's Galileo spacecraft. The C9 images were obtained on June 28, 1997 at a range of more than 600,000 kilometers (372, 000 miles).
Image Title: Color Mosaic and Active Volcanic Plumes on Io
Catalog #: PIA01081
Target Name: Io
Spacecraft: Galileo Orbiter
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Last Modified On: Monday, December 18, 2000