Back when the first issue of discover hitrnthe newsstands, the solar system was a sleepy place. We had nine planets and dozens of moons, but they seemed like inert, dead places-to the extent that we knew them at all. No action, no change.rnToday the picture couldn't be more different. NASA probes have found evidence of geological activity on at least three planetary bodies: Jupiter's hellish moon Io, Saturn's Enceladus, and Neptune's Triton. The Mars Reconnaissance Orbiter has documented landslides and dust devils on the Martian surface. Observers around the world saw Jupiter whacked by impacts on three occasions, including the dramatic multiple beating it took in 1994 by the comet Shoemaker-Levy 9.
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