Tiny Asteroid with Ring System a Surprising First Find for Astronomers

Astronomers have spotted an asteroid with Saturn-like rings, the smallest celestial body ever to be documented with a ring system.

Writing in the journal Nature, an international team of astronomers describe their discovery on the asteroid Chariklo, which is only 250 km wide.

Ring systems are typically associated with giant planets such as Saturn and Uranus, which dwarf an asteroid like Chariklo .

Chariklo belongs to a class of space objects called Centaurs, which have irregular orbits and properties resembling both asteroids and comets. These distant objects are difficult to study because of their their small size and how far away they are, and astronomers were only able to spot the rings around Chariklo when the light from a disant star became blocked when Chariklo passed in between that star and Earth last summer, the Nature blog reported.

As astronomers were observing the anticipated dip in brightness as the asteroid traversed the star, they noticed something else peculiar - two smaller dips in brightness. This anomaly led them to the evidence of rings around the asteroid, one 7 kilometers wide, the other 3 km wide and separated from the other by a 9 km gap.

"For me, it was quite amazing to realise that we were able not only to detect a ring system, but also pinpoint that it consists of two clearly distinct rings," research team member Uffe Gråe Jørgensen of the Niels Bohr Institute, University of Copenhagen, said in a statement. "I try to imagine how it would be to stand on the surface of this icy object -- small enough that a fast sports car could reach escape velocity and drive off into space - and stare up at a 20-kilometer wide ring system 1000 times closer than the Moon."

"Our best guess for the origin of the rings is that there was a collision on Chariklo and that this collision injected a disc of material around the body," Bruno Sicardy, from the Paris Observatory, France, told BBC News.

By studying the composition of the rings, astronomers will be able to get clues about their origin, James Bauer, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, California, told the Nature blog.

Baurer said that it is unlikely given the thousands of small bodies in the solar system that have not been studied that Chariklo is the only asteroid with a ring system.

"I think there is a good chance we'll see another ring system around a small body, somewhere in the outer Solar System," he said. "If you start birdwatching and see a bird for the first time, the chances are it's going to be a common bird."