In explaining and describing the forces that shape the bubble of solar wind surrounding the Sun, space physicists confront a dearth of information. But observations from space should soon alleviate this situation. Three spacecraft moving away from the Sun—Pioneer 10 and Voyagers 1 and 2—are expected to penetrate the boundaries of the heliosphere within the next few years. All three spacecraft first passed close to Jupiter, but now their extended missions have become exploration of the outer heliosphere.
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