Space rock 10199 Chariklo is no threat to Earth. The small celestial body — about 250 kilometers (155 miles) in diameter — has an orbit around the sun that places it between Saturn and Uranus, meaning that until recently, astronomers had no call to look closely at it. But when Chariklo passed in front of star UCAC4 248-108672 in June last year, astronomers at observatories in South America decided to take a closer look, and found something unexpected: like a miniature version of one of our solar system's gas giants, 10199 Chariklo has a system of rings.

Astronomers spotted noticeable dips in the brightness of UCAC4 248-108672 as the rock passed in front of the star relative to Earth. One large dip was caused by Chariklo itself occluding the star, but the light was also momentarily reduced by something on either side of the body. The astronomers determined the cause of the occlusion to be two rings of orbiting material. Felipe Braga-Ribas, astronomer at Brazil's Observatório Nacional, explained his shock. "We weren't looking for a ring and didn't think small bodies like Chariklo had them at all, so the discovery — and the amazing amount of detail we saw in the system — came as a complete surprise!"

10199 Chariklo's two rings are called Oiapoque and Chuí

The rings are currently known as Oiapoque and Chuí, named for two Brazilian rivers. The rock they orbit is not technically an asteroid: 10199 Chariklo is half-asteroid and half-comet, its irregular and unstable orbit classifying it as a "Centaur." It's the largest of the Centaurs spotted in the area, but it also holds another distinction — it's by far the smallest object astronomers have ever observed to have its own set of rings.