NASA celebrated THE Galileo spacecraft's first year in orbit around the giant planet Jupiter on 7 December, 1996. The highlights among its hundreds of images have not been of the planet itself, however, but of its four giant moons, Ganymede, Callisto, Io and Europa. These are called the Galilean moons, after Galileo Galilei, who is credited with development of the first telescope in 1610 and used it to spot the four moons changing their positions as they circled Jupiter. These are mere spots of light viewed from Earth, but they were revealed as miniature planets by the Galileo's predecessors, the Pioneer and Voyager. The Galileo was deployed from the Space Shuttle Atlantis/STS34 in October 1989, and the images taken from it of two of the moons, Io and Europa, are particularly spectacular.
Pock-face
This is the best and highest-resolution image ever taken of the moon Io, a world of sulphur volcanos and geysers which spew sulphur dioxide and other gases high into space. This unique view also shows the atmosphere of Jupiter as a backdrop (seen as blue in this near-infra-red view). The black and red materials on Io's pock-marked face reveal the most recent volcanic deposits, probably just a few years old. The active volcano Prometheus is near the centre.
Source: Flight International
