NASA'S Hubble Space Telescope has taken a rare joint portrait of Jupiter and its volcanically active moon Io, as the moon passes above the turbulent clouds of the giant gas planet.

The image, taken on July 24 by the Wide Field Planetary Camera 2, is one of a series of images of Io being taken by Hubble to complement close- up images of Jupiter currently being taken by NASA's Galileo spacecraft, now in orbit around the planet. The first images of Io from Galileo have shown active volcanic plumes and obvious surface changes since the two Voyager spacecraft imaged the moon during their Jupiter flybys in 1979.

The conspicuous black spot on Jupiter visible in the crisp black-and- white image is Io's shadow. The shadow, about the size of Io (2,262 miles across), sweeps across the face of Jupiter at 38,000 miles per hour as the moon orbits 261,600 miles overhead. The smallest details visible on Io and Jupiter are about 100 miles across. Bright patches visible on Io are regions of sulfur dioxide frost. Io is roughly the same size as Earth's Moon.

Though the images from Galileo show much finer detail, Hubble provides complementary information because it can observe Io at ultraviolet wavelengths not seen by Galileo. Hubble also can observe Io at different times than Galileo, and can view Io under more consistent viewing conditions.

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                                   GIF                     JPEG 
PRC96-30  Jupiter and Io      gif/iotrans.gif         jpeg/iotrans.jpg

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