An asteroid with a dual set of rings is the first body in the solar system of its type ever discovered. This is the first object ever found to have a ring system, except for the four Jovian planets. Discovery of this remarkable feature was made by accident.
Chariklo is a rocky body, 155 miles in diameter that orbits the Sun between the planets Jupiter and Neptune. It was first discovered in 1997, by James Scotti of the Spacewatch program. This object is extremely dark, making it difficult to see in visible wavelengths. When the object was due to pass in front of a dim star, astronomers watched the occultation to measure the exact size of the asteroid.
Astronomers at the European Southern Observatory's La Silla telescope in Chile were one of the seven teams watching the event. They used the "Lucky Imager" that takes 10 pictures a second. They were surprised to find light from the star quickly disappeared twice, then went out for a longer period, then blinked twice more. This showed the light was blocked by a pair of rings surrounding the tiny body.
"It is a similar technique to how the rings of Uranus were discovered and the ring arc of Neptune. This is a great technique for finding faint rings, and the evidence is very credible," James Bauer, planetary astronomer at the Jet Propulsion Laboratory, told the press. Bauer was not involved in the discovery.
The pair of rings surrounding Chariklo are made up from particles of ice and rocky debris. One ring is two miles wide, while the other stretches four miles from one side to another. The pair are separated from each other by an estimated 5.5 miles.
Astronomers are uncertain how the ring system could have formed, or how long they have existed. Most ideas so far center around the idea of collisions creating the debris necessary for the formation of the ring system. It is possible another asteroid collided with Chariklo, and either kicked up ice or shattered, forming the ring system. Another idea is that two small moons of the asteroid collided, forming the ring structure.
The small boulders and pieces of debris may be kept in place partly through the presence of small natural satellites that have not yet be discovered.
"[The rings] may be the remnants of a debris disk, possibly confined by embedded, [half-mile wide] satellites," researchers wrote in the article announcing the discovery.
Discovery of rings around Chariklo suggests other smaller bodies in the solar system may also possess similar features.
