Introduction to special issue

Voyage of Discovery

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Science  23 Sep 2005:
Vol. 309, Issue 5743, pp. 2015
DOI: 10.1126/science.309.5743.2015

Voyager 1 was launched on 5 September 1977. Eighteen months later, when it flew by Jupiter and its moons, it began to change our understanding of our solar system. Now, three decades later, it is still doing so.

Passing Jupiter, Voyager 1 discovered nine active volcanoes on the moon Io: the first evidence of a geologically active body elsewhere in our solar system (eight were still active a few months later, when Voyager 2 passed). It also mapped the fractured icy surface of Europa and other moons, studied a huge storm in Jupiter's atmosphere, found that Jupiter had a ring (changing theories about planetary rings) and a magnetic field (changing planetary radio science), and analyzed a variety of new plasma interactions in Jupiter's atmosphere (Science, 1 June 1979*). The next stop, just over 1 year later, was Saturn (Science, 10 April 1981). Here, Voyager 1 found gaps and structure in Saturn's rings and several new moons. It discovered lightning in Saturn's atmosphere. It closely observed Titan, showing that it, like Earth, had a nitrogen-rich atmosphere and dynamic clouds. Its close flyby of Saturn flung Voyager on a long, mostly quiet journey heading out of the solar system. Nearly 25 years after passing Saturn, it is now the farthest-traveled human object.


Four Reports and a Viewpoint in this issue describe Voyager 1's next encounter, with the heliosheath. The heliosheath begins where the solar wind, expanding outward at supersonic speeds, meets interstellar material and slows abruptly, forming a shock wave. This shock expands and contracts with the solar cycle; Voyager 1 crossed it at about 95 astronomical units (AU) from the Sun in December 2004 (Pluto orbits about 40 AU from the Sun). Data returned from Voyager 1 provided an in situ view of this shock (called the termination shock) and its effects on cosmic rays and the solar magnetic field, and of particles and plasmas in the heliosheath. As it has in the past, Voyager's observations have changed our view of the solar system, challenging notions about the origin of certain cosmic rays that were thought to be produced in this region. Voyager 1 will continue to collect data while heading toward an even larger shock marking the edge of our solar system (see the cover for an example), perhaps entering interstellar space in 10 to 20 years. Given the past success of Voyager 1, and of its partner, Voyager 2, which is also approaching the heliosheath after exploring all the giant planets, perhaps we should stay tuned.

  • * These issues of Science, and all others going back to the first issue, are available at and to members of the American Association for the Advancement of Science.

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