Chariklo: First Asteroid With Rings

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The Centaur minor planet with its ring system. European Southern Observatory

Saturn used to be the only place in the solar system we knew of that had rings. They gave it an eerie, alien appearance through a telescope. Then, using better telescopes and spacecraft missions that flew by the outer planets, astronomers found out that Jupiter, Uranus, and Neptune also had ring systems. That spurred a great deal of scientific re-thinking about rings: how they form, how long they last, and what kinds of worlds could have them.

Rings Around an Asteroid? 

The situation is still changing, and in recent years, astronomers discovered a ring around a minor planet called Chariklo. It's what they call a Centaur-type asteroid. That's a small body in the solar system that crosses orbits with at least one giant planet. There are at least 44,000 of these little worldlets, each measuring at least a kilometer (0.6 miles) across or larger. Chariklo is quite large, about 260 kilometers (about 160 miles) across—and is the largest Centaur found so far. It orbits the Sun out between Saturn and Uranus. Centaurs are not dwarf planets like Ceres, but objects in their own right.

How did Chariklo get its rings? It's an interesting question, especially since no one ever considered that such small bodies COULD have rings. The best idea put forth so far is that ancient Chariklo may have been involved in a collision with some object out in its neighborhood. That's not unusual—many worlds of the solar system were largely formed and shaped through collisions. Earth itself has been affected by collisions.

It's possible that a moon of one of the gas giants was tidally "shoved" into Chariklo's path. The resulting crash would have sent a lot of debris spinning out to space to settle into orbit around this little world.

Another idea is that Chariklo could have experienced a kind of "cometary" activity when material from under its surface sprayed to space. It would have created the ring. Whatever happened, it left this world with a ring of particles that contain water ice and are only a few miles wide. Scientists have named the rings Oiapoque and Chui (after rivers in Brazil). 

Looking for Rings in Other Places

So, do other Centaurs have rings? It would make sense to find more that do. They could be experiencing collisions and outgassing events that leave debris in orbit around them. Astronomers have looked around Chiron (the second-largest Centaur) and found evidence for a ring there, too. They used an event called a "stellar occultation" (where a distant star is covered by Chiron as it orbits the Sun). The light from the star is "occulted" not only by the Centaur ​but also by any material (or even an atmosphere) around that world. Something is blocking the light from the star, and that could be ring particles. It could also be a shell of gas and dust or possibly even some jets shooting material up from Chiron's surface.

Chiron was the first one discovered, in 1977, and for a long time, astronomers assumed Centaurs were not active: no volcanism or tectonic activity. But, mysterious brightenings of Chiron set them to thinking again: maybe something's going on at them. Studies of light from occultations showed traces of water and dust at Chiron. Further studies turned up the tantalizing promise of a possible ring system. 

If they do exist, Chiron's two possible rings would stretch out some 300 kilometers (186 miles) from the center of Chiron and would be about 3 and 7 kilometers (1.2 and 4.3 miles) wide. What could cause these rings? Certainly the jets of material that have been inferred from other observations could be populating a ring system. Astronomers see a similar "populating" going on at Saturn, where jets of material from the moon Enceladus are populating the nearby E ring.

It's also entirely possible that Chiron's rings (and those around other Centaurs, when found) could be the leftovers of their formation. That makes sense since their formation involved collisions and close encounters between rocky bodies. This leaves a lot of work for astronomers to do, uncovering other rings and explaining the ones that do exist. The next steps will be to answer such questions as "How long will the rings last?" and "How are such rings sustained?" Scientists who are working on defining the rings around Chiron will continue looking for more evidence and answers. 

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Petersen, Carolyn Collins. "Chariklo: First Asteroid With Rings." ThoughtCo, May. 22, 2018, thoughtco.com/asteroid-rings-3072201. Petersen, Carolyn Collins. (2018, May 22). Chariklo: First Asteroid With Rings. Retrieved from https://www.thoughtco.com/asteroid-rings-3072201 Petersen, Carolyn Collins. "Chariklo: First Asteroid With Rings." ThoughtCo. https://www.thoughtco.com/asteroid-rings-3072201 (accessed May 28, 2018).