<P> In 1859, James Clerk Maxwell demonstrated that a nonuniform solid ring, solid ringlets or a continuous fluid ring would also not be stable, indicating that the ring must be composed of numerous small particles, all independently orbiting Saturn . Later, Sofia Kovalevskaya also found that Saturn's rings cannot be liquid ring - shaped bodies . Spectroscopic studies of the rings carried out in 1895 by James Keeler of Allegheny Observatory and Aristarkh Belopolsky of Pulkovo Observatory showed Maxwell's analysis was correct . </P> <P> Four robotic spacecraft have observed Saturn's rings from the vicinity of the planet . Pioneer 11's closest approach to Saturn occurred in September 1979 at a distance of 20,900 km . Pioneer 11 was responsible for the discovery of the F ring . Voyager 1's closest approach occurred in November 1980 at a distance of 64,200 km . A failed photopolarimeter prevented Voyager 1 from observing Saturn's rings at the planned resolution; nevertheless, images from the spacecraft provided unprecedented detail of the ring system and revealed the existence of the G ring . Voyager 2's closest approach occurred in August 1981 at a distance of 41,000 km . Voyager 2's working photopolarimeter allowed it to observe the ring system at higher resolution than Voyager 1, and to thereby discover many previously unseen ringlets . Cassini spacecraft entered into orbit around Saturn in July 2004 . Cassini's images of the rings are the most detailed to - date, and are responsible for the discovery of yet more ringlets . </P> <P> The rings are named alphabetically in the order they were discovered . The main rings are, working outward from the planet, C, B and A, with the Cassini Division, the largest gap, separating Rings B and A. Several fainter rings were discovered more recently . The D Ring is exceedingly faint and closest to the planet . The narrow F Ring is just outside the A Ring . Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales, some related to perturbations by Saturn's moons, but much unexplained . </P> <P> The dense main rings extend from 7,000 km (4,300 mi) to 80,000 km (50,000 mi) away from Saturn's equator, whose radius is 60,300 km (37,500 mi) (see Major subdivisions). With an estimated local thickness of as little as 10 m and as much as 1 km, they are composed of 99.9% pure water ice with a smattering of impurities that may include tholins or silicates . The main rings are primarily composed of particles ranging in size from 1 cm to 10 m . </P>

What do you call the rings around saturn
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