December 20, 2014
Step aside Saturn: Little asteroid has rings too
It is not just Saturn and the giant gas planets of the solar system that bear rings. For the first time, rings have been found around an asteroid, a study published today shows.
The asteroid, known as Chariklo, is more than 621 million miles (1 billion km) from Earth, circling the sun in an orbit between Saturn and Uranus.
On June 3, 2013, astronomers at seven different locations in Chile, Brazil, Uruguay and Argentina were standing by to observe the asteroid as it passed in front of star, relative to the telescopes' lines of sight. They hoped the dips in starlight, caused by the asteroid passing in front of the star, would reveal details of the 154-mile (248-km) asteroid's size and shape.
They ended up with much more. Analyzing flickers of light during the occultation revealed two dense rings circling Chariklo.
Previously, only the giant planets Saturn, Jupiter, Uranus and Neptune were known to have rings.
"We weren't looking for a ring and didn't think small bodies like Chariklo had them at all," lead astronomer Felipe Braga-Ribas, with Brazil's National Observatory in Rio de Janeiro, said in a statement. "The discovery ... came as a complete surprise."
Chariklo's rings have crisp edges, a feature typically caused by the gravitational effects of a small embedded moon or moons.
"It's likely that Chariklo has at least one small moon still waiting to be discovered," Braga-Ribas said.
Chariklo's inner ring is 4.3 miles (7 km) wide and the outer ring is 1.9 miles (3 km) wide. The bands are separated by a 5.6 mile (9 km) wide gap.
"It was quite amazing to realize that we were able not only to detect a ring system, but also pinpoint that it consists of two clearly distinct rings," astronomer Uffe Grae Jorgensen, with the University of Copenhagen in Denmark, said in a statement.
The origin of the rings is not known, but scientists suspect they formed after another body crashed into Chariklo, forming a debris disk of icy particles.
The research is published in this week's issue of the journal Nature.