First Ring Around Jupiter Is Discovered

Jupiter became the third planet known to possess a ring; it was photographed by the Voyager 1 probe and raised new questions about the physical properties of the Jovian system.


Detection of the Jovian rings provides both an object lesson in the nature of thought processes at work in scientific communities and important new information about the character of the outer solar system. The enormous quantities of data returned by the Voyagers also raised entirely new questions concerning planetary and solar system origins. Uranus (planet);occultation mission

Clearly, some scientists became so entrapped in the theoretical models required to explain the long-known rings of Saturn that they failed to interpret correctly several kinds of pre-Voyager data suggesting the presence of Jovian rings. One wrote off the drop in radiation levels near the equator of Jupiter (first recorded by Pioneer 10 six years before Voyager 1 photographed the rings) as a false reading, possibly caused by equipment malfunction. The Hawaii team that obtained ground confirmation of the rings—using only a moderately large reflector with a mirror diameter of 2.2 meters—once alerted to look for the rings, accepted photographic evidence that most likely would not have led to the same conclusion before the Voyager 1 mission. The ring discovery showed that theories and models, valuable as they are for maintaining the elements of rigor and verification in research, occasionally lead scientists to look only for what they are predisposed to find and to overlook that which they previously have ruled out.

The Jupiter ring system, in itself, turned out to be a relatively minor chapter in a burst of discovery about the outer planets. The Uranus observations in 1977 and Voyager’s flyby of Jupiter in 1979 shattered ring theories based on Saturn models and collectively implied that ring systems are typical of the giant planets beyond Mars. The subsequent arrival of Voyager 2 at Saturn released a torrent of information about ring systems and underscored the relative simplicity of the Jovian ring. Voyager went on to explore the Uranus system in 1984, as astronomical evidence of a ring around Neptune appeared, and the Neptune ring was confirmed by direct observation in 1989.

The ring system around Jupiter has been incorporated into a far more complex set of models than most scientists could have perceived prior to the Voyager missions. Ring systems are not the smooth and uniform objects they were once thought to be. Instead, they contain myriad structures, many of which still elude explanation. The rings of Jupiter, although hardly as visually spectacular as the Saturn system, nevertheless appear to be more typical of ring formation and history than the major rings of Saturn. The Jupiter ring system, those of Uranus and Neptune, as well as some of the minor rings of Saturn, are all made up of extremely small particles and some, astonishingly close to their primaries, raise a host of unsolved questions. By far the most unsettling aspect of these rings is that many of them appear to be much younger than the estimated 4.5-billion-year age of the solar system. So, too, do most of the tiny shepherd moons, particularly those well inside the Roche limit, wherein solid bodies should not be able to survive the gravitational stresses caused by their primaries.

Computer models suggest that satellites with diameters of about 20-50 kilometers, lodged amid the debris of the rings and subject to fierce radiation, could not survive much longer than one billion years. Smaller bodies might be even younger, perhaps only a few thousand years old.

Jupiter’s ring system, like most, is ever changing. Material attaches to the shepherd moons, while other material is stripped away by radiation and other effects. Shepherd moons may sweep clean for a time wide swaths in the particle belts. Most of the rings appear doomed to destruction by the forces around them, but others will replace them. The rings of Jupiter belong to a planetary system almost as complex as the solar system itself, a dynamic and incredibly varied system the study of which has breathed new life into planetary sciences. Astronomy;planets
Jupiter (planet);ring system
National Aeronautics and Space Administration;Voyager missions
Voyager missions
Planets;ring systems

Further Reading

  • Burns, Joseph A., Mark R. Showalter, Jeffrey N. Cuzzi, and James B. Pollack. “Physical Processes in Jupiter’s Ring: Clues to Its Origin by Jove!” Icarus 44 (1980): 339-360. Discussion of the physical forces involved in creating and maintaining Jupiter’s tenuous ring system. Recounts early theories proposed before discovery of the shepherd moons and the mechanics of the shepherd system.
  • Cuzzi, Jeffrey N., and Larry W. Esposito. “The Rings of Uranus.” Scientific American 257 (July, 1987): 52-66. The best discussion in popular scientific literature of the dynamics of narrow, dusty rings such as those around Uranus and Jupiter. Particularly useful on the nature of shepherd moons.
  • Elliot, James, and Richard Kerr. Rings: Discoveries from Galileo to Voyager. 2d ed. Cambridge, Mass.: MIT Press, 1987. Highly readable and nontechnical account of the series of ring discoveries around Jupiter, Saturn, and Uranus from 1977 to 1986. Authors describe these as one of the major scientific events of the late twentieth century and discuss problems and theories derived from them. Useful account of technology involved in the discoveries and of the human element of excitement in the research teams.
  • Esposito, Larry W. “The Changing Shape of Planetary Rings.” Astronomy 15 (September, 1987): 6-15. Excellent summary, by the chair of the Voyager Rings Science Working Group, of a decade of discovery. Shows that the trend of research supports theories that the Jovian rings—and probably those of Uranus as well as some Saturnian rings—may be much younger than their primary planets.
  • Harland, David M. Jupiter Odyssey: The Story of NASA’s Galileo Mission. London: Springer-Praxis, 2000. A detailed scientific and engineering history of the Galileo program, but also includes extensive discussion of Voyager program events and results.
  • Irwin, Patrick G. J. Giant Planets of Our Solar System: Atmospheres, Composition, and Structure. London: Springer-Praxis, 2003. Provides an in-depth comparison of Jupiter, Saturn, Uranus, and Neptune, incorporating data obtained from astronomical observations and planetary spacecraft encounters.
  • Jewitt, D. C., and G. E. Danielson. “The Jovian Ring.” Journal of Geophysical Research 86 (1981): 8691-8697. Early summary of apparent physical properties of the rings and questions raised of origin and maintenance under measured conditions.
  • Owen, Tobias, et al. “Jupiter’s Rings.” Nature 281 (1979): 442-446. The initial report from the research team on the existence of the rings. Summarizes properties and problems presented by the discovery.
  • Smith, Bradford A., et al. “The Jupiter System Through the Eyes of Voyager.” Science 204 (1979): 927-950. Summary of observations of the Voyager spacecraft, which places the rings in context with other knowledge about the Jovian system.

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