Europa, the ice-covered moon of Jupiter, has a problem that turns out to be a clue. Almost nothing has left a lasting mark on it. In a Solar System that has been pelting its planets and moons with rock and ice for four and a half billion years, an old surface should be crowded with […] Europa, the ice-covered moon of Jupiter, has a problem that turns out to be a clue. Almost nothing has left a lasting mark on it. In a Solar System that has been pelting its planets and moons with rock and ice for four and a half billion years, an ol... [2855 chars]