10199 Chariklo

10199 Chariklo is a special kind of object in space called a ringed asteroid and centaur. It lives in the outer part of our Solar System, moving between the planets Saturn and Uranus. Chariklo is the largest known centaur, with a size of about 250 kilometers or 160 miles across. It was found on February 15, 1997, by scientists at the University of Arizona’s Spacewatch project at the Kitt Peak National Observatory.

What makes Chariklo truly unique is its ring system. In 2013, astronomers discovered that Chariklo has two thin rings made of icy particles orbiting around it. Chariklo was the first tiny planet ever found to have rings. As of 2025, it is one of only four minor planets known to have rings, along with 2060 Chiron, Haumea, and Quaoar. Scientists are still trying to figure out why Chariklo’s rings stay in place, since they were expected to break apart quickly. Some think that tiny, unseen shepherd moons might be helping to keep the rings stable. The rings might have come from material thrown off Chariklo’s surface or from a moon that broke apart long ago.

Discovery and naming

Chariklo was found on February 15, 1997, by the University of Arizona’s Spacewatch project at Kitt Peak National Observatory. James V. Scotti helped make the discovery using a special telescope, though official records don’t list him as the discoverer. Observatories in Canada, the Czech Republic, and China also watched Chariklo until its discovery was announced on February 24, 1997. It was given the temporary name 1997 CU₂₆ and was the seventh centaur ever found.

Soon after its discovery, scientists studied Chariklo to learn more about it. By March 2, 1999, it received the official number 10199. It was finally named on September 28, 1999. The name comes from Chariclo, a figure in Greek mythology who was the wife of Chiron. She is sometimes described as a sea nymph, a female centaur, or the mother of the prophet Tiresias. An astrologer later created a special symbol for Chariklo based on the symbol for another centaur named 2060 Chiron.

Orbit

Chariklo travels around the Sun between Saturn and Uranus with an average distance of 15.7 astronomical units. It takes Chariklo 62.5 years to complete one orbit around the Sun. Its path is tilted and stretched out, bringing it as close as 13.1 astronomical units to the Sun and as far as 18.4 astronomical units away.

Chariklo is called a centaur because it orbits between Jupiter and Neptune. Centaurs share traits of both asteroids and comets. They are thought to come from areas far beyond Neptune, called the Kuiper belt and the scattered disc. The gravity of large planets like Jupiter and Neptune can change their paths in unpredictable ways. These changes can cause centaurs to leave their area, either by being thrown out of the Solar System, hitting a planet, or becoming a comet that moves closer to the Sun.

Compared to other centaurs, Chariklo’s orbit is more stable. It has a 50% chance of leaving the centaur region in about 7 to 10 million years. Chariklo’s orbit is mostly affected by Uranus, and it will likely come close to Uranus many times over the next 100 million years. Future encounters with Jupiter and Saturn could have bigger effects on Chariklo’s path and might even affect its ring system.

Observation

Chariklo's brightness, or how bright it looks from Earth, changes between 17 and 19 depending on how far it is from us. It looked its brightest in 2003 when it was closest to Earth and the Sun at the same time. Chariklo's brightness also changes because its rings can look bigger or smaller depending on how we see them from Earth.

Chariklo and its rings are too small and far away for today's telescopes to see clearly. Special events called stellar occultations, when Chariklo passes in front of stars, help scientists measure Chariklo's size and rings very accurately. These events led to the discovery of Chariklo's rings in 2013, and many observations since then have been made by teams of professional and amateur astronomers working together.

Physical characteristics

Chariklo is a large asteroid shaped like an oval, with dimensions of about 288 km × 270 km × 198 km (179 mi × 168 mi × 123 mi). Its average diameter is roughly 250 km (160 mi), making it the largest known centaur — a type of object that orbits the Sun between Saturn and Uranus.

The surface of Chariklo looks dark and reddish. In certain types of light, its surface seems to contain water ice, minerals, and complex organic materials. Unlike some similar objects, Chariklo does not show signs of activity like a dusty tail or jets, likely because it is too cold and far from the Sun. However, in the past, it might have been closer to the Sun and more active.

Rings

Main article: Rings of Chariklo

In 2013, scientists discovered that the asteroid Chariklo has two rings. These rings are about 386 and 400 kilometers wide, with the inner ring being about 6.9 kilometers wide and the outer ring being just 0.12 kilometers wide. The rings are roughly 14 kilometers apart from each other.

Finding rings around a small object like Chariklo was a big surprise because rings were thought to only exist around much larger objects. Scientists believe these rings might not last very long unless something is keeping them in place. They named the inner ring Oiapoque and the outer ring Chuí after rivers in Brazil. It’s also possible that another object, Chiron, might have rings too.

Exploration

Main article: Camilla (spacecraft)

There is an idea for a space mission called Camilla, first talked about in June 2018. This mission would send a robot spacecraft to fly past the asteroid Chariklo. During the flyby, the spacecraft would release a small object made of tungsten to create a crater for scientists to study from far away.

The mission would try to stay within budget rules set by NASA. If it happens, the spacecraft would launch in September 2026. It would use the gravity of Venus and Earth to help it travel towards Jupiter.