Rings of Saturn
Huygens' ring hypothesis and later developments

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 (13,000 mi). 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 (39,900 mi). 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 (25,000 mi). 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.
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