Which planets have ring systems?
Sen—In July 1610 Italian astronomer Galileo Galilei saw something curious through his new telescope. Saturn appeared to be accompanied by two smaller bodies either side. Other observers noted instead how Saturn appeared 'oval'. It was only in 1655 when Dutch astronomer Christiaan Huygens turned a more-improved telescope towards the planet that he was able to see it surrounded by a 'disc'—something unknown in astronomy up until then.
Today we call this structure, 282,000 kilometers in diameter, the 'rings' of Saturn. And although Huygens thought it was solid, we now know it's composed of billions upon billions of fragments, ranging from the size of houses down to fine specks of dust.
The fragments are composed of 99.9 per cent water ice with a small amount of other chemicals. Each one of these fragments is in its own orbit around the planet. The ring system is by-far the gas planet's most impressive feature. Though undoubtedly the most impressive ring system in our Solar System, Saturn is not the only planet which has rings.
The next most prominent rings belong to Uranus—a smaller, colder gas planet over twice as far from us as the 1.2 billion kilometer-distant Saturn. The rings weren't discovered until 1977, and the first good view was by NASA's Voyager 2 probe during a fly-by in 1986.
Uranus's main rings are narrower than Saturn's numerous tori. They're composed of fragments up to 20 meters in size and are darker than Saturn's. They span 98,000 kilometers in diameter and their chemical composition is a mystery.
The rings of Uranus as imaged by the Hubble Space Telescope. Image credit: NASA/ESA/M. Showalter (SETI Institute).
The two other giants in our Solar System, Jupiter and Neptune, also have rings. But these can't be seen from Earth as they're too faint.
Space probes detected a three-structure ring system around Jupiter in 1979. A thin, outer region called the 'Gossamer rings', a main, flat central ring and a thinner, inner ring called the 'Halo'. They're created by the fine dust thrown off by Jupiter's moons and span 214,200 kilometers in diameter.
Neptune has five main rings which were discovered by Earth-based observations in 1984. In 1989 they were imaged by Voyager 2 during its flyby.
Like Jupiter, Neptune's 63,000 kilometer-diameter rings are very tenuous and, like Uranus, are very dark.
And it isn't only giant planets with ring systems. Centaurs, small icy bodies making their way from beyond Neptune in the Kuiper Belt, where they likely originated, in towards the inner Solar System, may also have rings.
Observations of the largest Centaur, Chariklo, which measures 248 by 258 by 302 kilometers, have shown it to have two rings. Evidence has also been found for rings/arcs of material around Chiron, the first Centaur discovered and the second largest of the known population.