UNC-TV Science: Chariklo

UNC-TV Science: April 7, 2014
Chariklo: The Asteroid that Wears Itself Like a Planet

Planets are the traditional bearers of rings. The four giants – Jupiter, Saturn, Uranus and Neptune – sit within these concentric fields of rocks and ice. In Saturn’s case, its rings dominate its appearance.

For decades, scientists thought that within our solar system, these four planets were unique in their possession of rings. Indeed, the reigning theory suggested only planets and the sun command enough gravity to hold onto all of the tiny pieces that make up a ring system.

Now, an international team of astronomers, including Appalachian State University professor Joseph Pollock has discovered the first asteroid to ever display a ring system.

Photo Courtesy of European Southern ObservatoryWith a diameter of 250 km, the asteroid, called Chariklo, is the fifth and by far the smallest object ever seen with rings. To put that in perspective, driving a lap around Chariklo would be similar to driving from Raleigh to New York City. It belongs to a class of objects called centaurs, which orbit the sun in the vast region of space between Jupiter and Neptune.

Its two rings are densely packed and very thin: just seven and three meters wide respectively with a nine meter space in between.

The team of astronomers reported they discovered the rings by accident. They were trying to more accurately determine Chariklo’s shape by observing what is called an occultation. Occultation occurs when an object passes in front of a star from our point of view on Earth, very much like an eclipse. Astronomers measure the light from the star, and when the object passes, it blocks that light from reaching the telescopes, like casting a shadow. Using the object’s speed and the duration of its shadow, scientists can determine the object’s size.

For a single object, you would expect one long shadow, but when the astronomers measured Chariklo from several observatories in South America, they saw something different. They saw two very brief shadows just before Chariklo’s main body passed over the star and two identical ones just after. These were the rings.

Check out this video from Nature to see what the occultation would have looked like.

The next task for astronomers is to determine how Chariklo’s rings got there in the first place. The team hypothesized that the rings may be the result of Chariklo’s impact with a smaller asteroid. This is how our moon was born, and if Chariklo’s rings indeed formed this way, Chariklo may have a moon of its own in a few million years.

While Chariklo is the first asteroid we’ve seen with rings, this discovery opens the door for other possible ring systems around asteroids. In the study, published in the journal Nature, the astronomers report that they are not sure whether Chariklo’s rings come from some common process or whether it is unique.

- Daniel Lane

Daniel Lane covers science, medicine and the environment as a reporter/writer. He is currently pursuing a master's degree in medical and science journalism at UNC - Chapel Hill.