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Volcanoes on Io
This color image, acquired during Galileo's ninth orbit 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 after a South American god of thunder, fire and volcanoes. The plume seen by Galileo is 140 kilometers (86 miles) high and was also detected by the Hubble Space Telescope. The Galileo spacecraft will pass almost directly over Pillan Patera in 1999 at a range of only 600 kilometers (373 miles).The second plume, seen center near the terminator (boundary between day and night), is called Prometheus after the Greek fire god. The red shadow of the 75-kilometer (45-mile) high airborne plume can be seen extending below the eruption vent (in the center of the bright and dark rings). Plumes on Io have a blue color, so the plume shadow is reddish (the remainder of white after blue is removed). 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. On the other hand, a plume has never been seen at Pillan Patera prior to the recent Galileo and Hubble Space Telescope images.
North is toward the right of the picture. The resolution is about 6 kilometers (3.7 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 images were obtained on June 28, 1997, at a range of more than 600,000 kilometers (372,000 miles).