Which Planets Have Rings?

19 Jun , 2014 by Video

You think only Saturn has rings? Well, think again. Rings are actually extremely common in our Solar System – they’re all over the place. So which planets – and other objects – sport rings?

Consider Saturn and its beautiful ring system. For most of human history, we had no idea planets could even have rings. Without a telescope, Saturn just looks like another bright star in the sky. But when Galileo turned his telescope to the heavens in 1610, he noticed that the planet had funny ears or handles on either side. He thought these might be moons connected to the planet.

Christiaan Huygens in 1655 first identified the rings as a disk around the planet, and not moons at all. And now with our modern telescopes and spacecraft, we can study Saturn in great detail. We can see dozens of minor gaps and rings, and small moons that shepherd the rings with their gravity. Saturn’s stretch out to a distance of almost 500,000 kilometers, but with a thickness of as little as 10 meters.

But Saturn isn’t the only planet in the Solar System with rings. In fact, there are a bunch. The next planet to be discovered to have rings is Uranus. These were discovered in 1977 by a team of astronomers who were looking to study the atmosphere. They were expecting it to pass in front of a star – known as an occultation – and were surprised when the light from the star dimmed and brightened several times before the event.

Rings of Uranus

Rings of Uranus

We now know there are 13 distinct rings around Uranus, and they’re tilted over on their side, just like the planet. Unlike Saturn, they are much thinner and darker, reflecting less of the light that hits them.

The next planet to be found with rings was Jupiter. It was found in 1979 by NASA’s Voyager 1 spacecraft which completed a flyby of the giant planet. Jupiter has four major rings, stretching out to an altitude of about 225,000 km. Jupiter’s rings are dusty, with all the ice blasted away by solar radiation and interaction with the gas giant. It seems that impacts on Jupiter’s moons replenishes the rings.

Jupiter's Rings

Jupiter’s Rings

The final planet with rings is Neptune, uncovered in 1984 by astronomers using the La Silla observatory in Chile. They were photographed by NASA’s Voyager II spacecraft in 1989. Neptune has 5 distinct and narrow rings, which are primarily made of dark dust.

Those are the only planets in the Solar System which have rings. It’s possible that some of the other planets had rings in the past, though. There could be events, like the break up of a Moon, or destruction of a comet that might have given Venus, Earth, or even Mars a temporary ring or two for a few million years.

The labeled ring arcs of Neptune as seen in newly processed data. The image spans 26 exposures combined into a equivalent 95 minute exposure, and the ring trace and an image of the occulted planet Neptune is added for reference. (Credit: M. Showalter/SETI Institute).

The labeled ring arcs of Neptune as seen in newly processed data. (Credit: M. Showalter/SETI Institute).

There might also be a ring system around Pluto. We’ll need to wait for close observations from New Horizons in 2015 to know for sure.

We now know that even asteroids have rings. In 2014, astronomers found a multiple ring system around the asteroid Chariklo. They watched how the light from a star dimmed as Chariklo passed in front. Just like Uranus, it dimmed slightly twice before the occultation, and twice after, indicating two rings.

Here’s the amazing thing. Astronomers have even discovered rings around an extrasolar planet. Using the SuperWASP telescope, they observed strange dimming as a planet passed in front of its parent star. The strange behavior means there’s a ring system around the planet, stretching out 60 million km out from the surface. That’s about 100 times bigger than Saturn. There are three main rings in the system, but astronomers think that each one could be made of thousands and thousands of smaller rings.

Since rings are so common in our Solar System, and these faint hints of rings in other systems, we can safely assume we’ll find rings systems everywhere in the Milky Way.

What do you think? Where else in the Universe should we go looking for rings?

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June 22, 2014 4:25 PM

Hey Fraser
SuperWASP’s discovery paper of that ring-system is here: http://arxiv.org/abs/1108.4070