IN 1610, in one of the most dramatic early observations stemming from the invention of the telescope, Galileo Galilei discovered lo, Europa, Ganymede and Callisto — these, in ascending order of distance from the planet, are the four largest satellites of Jupiter. At the moment, NASA's Galileo spacecraft is on an odyssey that brings it close to'each of these Galilean moons. The spacecraft's findings may not be as revolutionary as those of Galileo himself, but they are nonetheless full of surprises and stimulation for planetary scientists. By this measure, the Galileo mission has already been a huge success.
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