Jupiter's rings are invisible from Earth and do not show any structure similar to the rings of Saturn or Uranus. The rings are made up of dust and rock fragments. They were discovered by Voyager 1 and further investigated by Voyager 2 in 1979. As they contain no ice the rings reflect little light, making them difficult to see. Four of Jupiter's smaller moons orbit within the ring system, and may well be the source of the material which constitutes the rings themselves. NASA's two Voyager spacecraft were launched in 1977 to explore the planets in the outer solar system. Voyager 2 reached Jupiter in 1979 before flying on to reach Saturn in 1981, Uranus (1986) and Neptune (1989).
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