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PHOTO CAPTION                                     P-47935
                                                  October 18, 1996

Volcanic hot spots and auroral emissions glow on the dark side of Jupiter's
moon Io in the image at left. The image was taken by the camera onboard
NASA's Galileo spacecraft on 29 June, 1996 UT while Io was in Jupiter's
shadow. It is the best and highest-resolution image ever acquired of hot
spots or auroral features on Io. The mosaic at right of 1979 Voyager images
is shown with an identical scale and projection to identify the locations of
the hot spots seen in the Galileo image. The grid marks are at 30 degree
intervals of latitude and longitude. North is to the top.

In the nighttime Galileo image, small red ovals and perhaps some small green
areas are from volcanic hot spots with temperatures of more than about 700
kelvin (about 1000 degrees Fahrenheit). Greenish areas seen near the limb,
or edge of the moon, are probably the result of auroral or airglow emissions
of neutral oxygen or sulfur atoms in volcanic plumes and in Io's patchy
atmosphere. The image was taken from a range of 1,035,000 kilometers (about
643,000 miles).

Launched in October 1989, Galileo entered orbit around Jupiter on December
7, 1995. The spacecraft's mission is to conduct detailed studies of the
giant planet, its largest moons and the Jovian magnetic environment. The Jet
Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of
Space Science, Washington, DC.