1) The rings of Uranus were unexpectedly discovered in 1977 when astronomers observed nine symmetrical dimming events before and after a star was occulted by Uranus, indicating the presence of a ring system. 2) Voyager photos in 1986 confirmed Uranus has faint, narrow rings that are darker than Saturn's rings and are confined by shepherd moons. 3) Jupiter's ring was suggested based on 1974 data but was directly photographed by Voyager in 1979, revealing it to be faint and not visible from Earth with smaller particles than Saturn's rings.

1. Planetary Ring Systems
Saturn's Rings
Saturn's spectacular ring system was first discovered by Christiaan Huygens with a telescope that
was very small by modern standards. It is easily visible from Earth with a small telescope, so
Saturn's rings are quite well known.

2. It is less well known that the other Jovian planets also have ring systems. They are not easily visible
and were not discovered until relatively recently.
Rings of Uranus
The rings of Uranus were discovered unexpectedly on March 10, 1977 by a group of astronomers led
by James Elliot. These astronomers were studying an occultation of the star, SAO 158687, by
Uranus. In an occultation, the planet passes in front of the star. Studying the starlight after it passed
through the atmosphere of Uranus would tell the astronomers something about the planet's
atmosphere.
However something unexpected happened. The star's brightness dimmed nine times before the
occultation and, in a symmetrical pattern, nine times after the occultation. Astronomers interpreted
these data as a system of nine rings orbiting Uranus. Fewer brightness decreases or the lack of a
symmetrical pattern would have suggested previously undiscovered moons. The symmetry of the
pattern however forced astronomers to conclude that Uranus has rings.
When the Voyager mission flew by Uranus in 1986, photos confirmed that Uranus has a faint ring
system. The rings are much narrower and darker than Saturn's rings. Voyager photos revealed
shepherd moons confining the narrow rings around Uranus. The darkness of the rings suggests the
individual ring particles are not icy like in Saturn's rings.
Jupiter's Ring
Mario Acuna and Norman Ness suggested, on the basis of indirect data from the 1974 Pioneer 11
flyby of Jupiter, that Jupiter might have a ring. At the time few astronomers took the suggestion
seriously. When the Voyager mission flew past Jupiter in 1979 however it directly photographed the
ring around Jupiter.
Unlike Saturn's easily visible ring system, Jupiter's ring is faint and not visible from Earth. The
individual particles in Jupiter's ring are much smaller than those in Saturn's rings. Many are perhaps
only a few millionths of a meter in diameter. Particles this small would not last very long. So, either
Jupiter's ring is, in astronomical terms, short-lived or the ring particles are replenished somehow.
Rings of Neptune

3. By 1979 astronomers knew that Saturn, Uranus, and Jupiter all had rings. So they asked if Neptune
also had rings. They had to wait a decade until the Voyager spacecraft reached Neptune to find the
answer.
Several astronomers tried to observe occultations of stars by Neptune to see if they could discover
rings like they were discovered around Uranus. These experiments produced conflicting results.
Some astronomers observed brightness decreases like those for Uranus. Others found no evidence
for rings. What was going on?
When the Voyager mission finally reached Neptune in 1989, photographs revealed five very thin
narrow rings. Two of the rings originally appeared as one ring. More interestingly however
Neptune's rings are clumpy. Some portions of a ring are thicker that other portions. The clumps
explain why the occultation experiments produced conflicting results. The experiments could detect
the thicker portions of the rings but not the thinner portions.
Saturn's rings are the most spectacular, but ring systems are a feature of all the gas giant planets in
the solar system.
Further Reading
Chaisson, E, and McMillan, S. Astronomy Today 5th ed., Pearson, 2005.
Beatty, J.K., O'Leary, B., and Chaikin, A. The New Solar System 2nd ed., Cambridge, 1982.
https://suite.io/paul-a-heckert/m372dj