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Dione reveals its past via contrasts in this view from NASA's Cassini spacecraft. The features visible here are a mixture of tectonics -- the bright, linear features -- and impact cratering -- the round features, which are spread across the entire surface. Tectonic features tell the story of how Dione (698 miles or 1,123 kilometers across) has been heated and cooled since its formation, and scientists use those clues to piece together the moon's past. Impact craters are evidence of external debris striking the surface, and thus they tell about the environment in which the moon has existed ove…
