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PHOTO CAPTION                                     P-47962
                                                  October 23, 1996

Scientists believe that water-ice frosts are the likely cause for the
brightening seen around the circular rims of these craters located at a high
northern latitude (57 degrees) on Jupiter's moon Ganymede in this image
taken by NASA's Galileo spacecraft on September 6, 1996. The image, just
recently radioed to Earth from the spacecraft, shows the same kind of
bright, high-latitude surface areas as those first seen by the Voyager
spacecraft in 1979, but at higher resolution (this image spans about 18
kilometers or 11 miles on a side). Even though the Sun is shining from the
south, the north-facing walls of the ridges and craters are brighter than
the walls facing the Sun. This is interpreted to mean that the very bright
north-facing slopes are covered with surface water- ice frosts, and that
these frosts preferentially accumulate in such high- latitude locations.
Galileo scientists say that at the high resolution seen in Galileo images,
the high-latitude brightness seen by Voyager is partly attributable to
frosts forming on cooler, north-facing slopes.

The right-hand side of the image is dominated by a north-south line of
impact craters; the smallest ones at the top are about 2 kilometers (1.2
miles) in diameter and the large one at the bottom is about 5 kilometers
(about 3 miles) in diameter. Ganymede is the largest moon in the solar
system, larger than the planet Mercury and nearly the size of Mars.

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.