Astro Rings

Astro Rings
Portrayal of Saturn with Cassini spacecraft

Saturn's vivid rings are well known, but it's not the only ringed planet. And it isn't only planets that have rings. The cosmos has a variety of ringed objects.

Planets with rings
With Saturn's rings known for a good three hundred years, it was something of a surprise suddenly to discover that the other giant planets were also ringed.

In 1977, astronomers observed a stellar occultation of Uranus. In an occultation, the star's light is blocked by the nearer object, such as a planet. This provides clues to features of the object being observed. The team studying Uranus was astonished. They were not expecting rings. A 1984 occultation gave the first evidence that Neptune probably had rings too. NASA's Voyager 2 later confirmed this.

But what about Jupiter? It's the closest of the giant planets, about half Saturn's distance from us. Yet no one had ever seen any sign of jovian rings. Until . . . the Space Age! In 1979, Voyager 1 surprised NASA scientists with an image of rings. Voyager 2 and later missions have provided even more detail of Jupiter's rings. Since the rings are faint and dusty, very large telescopes such as the Keck Observatory are needed to see them from Earth.

A ringed dwarf planet
It's not just giant planets that have rings. In 2017, astronomers observed an occultation of the dwarf planet Haumea. Studying the data, they realized that Haumea has two rings. It isn't the smallest body known to have rings, but it's the most distant Solar System object known to be ringed.

A ringed centaur
In a 2013 occultation, a system of two rings was found around 10199 Chariklo, a centaur orbiting the Sun between Saturn and Uranus. A centaur generally looks like an asteroid, but its composition is somewhat similar to a comet. The dual nature of such an object inspired the name centaur. In classical mythology, the centaurs were half human and half horse.

A mind-boggling ringed exoplanet
Around 435 light years from us in Centaurus, there lies a sunlike star called J1407. Its amazing planet has the lackluster name J1407b. The planet is bigger than Jupiter, and has a ring system some 200 times greater than Saturn's. It's too far away to observe the rings directly, but the discovery team modelled them using data from their observations. One of the team leaders said that “if we could replace Saturn's rings with the rings around J1407b, they would be easily visible at night and be many times larger than the full Moon." [An artist's conception of the rings by Ron Miller]

Messier 57
The Ring Nebula, also known as Messier 57, is some 2500 light years away in Lyra. It's a planetary nebula, created when a sunlike star sloughed off its outer layers as its nuclear fuel ran out. In the center of the Hubble image you can see the white dwarf that the star has become. (The other white dots are foreground objects.)

Hoag's Object
I love the magnificence of Saturn's rings, and the Ring Nebula is fascinating. But what in the known Universe can beat a ringed galaxy? Astronomer Art Hoag discovered the first one in 1950, and it's been named Hoag's Object. It's about 600 million light years away in Serpens, and it seems to be slightly larger than our Milky Way. The yellow nucleus is made up older stars, with young hot blue stars forming the ring. There may be also some star clusters in the gap, but none have yet been found.

You Should Also Read:
Haumea the Ringed Dwarf Planet
Giants and a Last Look Homeward

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