London, March 27: In a surprising find that indicates that rings surrounding planets may be a more common feature than previously thought, astronomers have now discovered rings around an asteroid-like body whose orbit is between those of Saturn and Uranus.
At just 250 kms away, Chariklo is the smallest celestial body so far found to have rings.
“The discovery was an accident and a surprise,” said lead author Felipe Braga-Ribas, an astronomer at the National Observatory in Rio de Janeiro, Brazil.
Chariklo belongs to a class of objects called “centaurs” which traverse the outer solar system in unstable orbits and can share characteristics with both asteroids and comets.
Because they are small, dark and far away, studying them is a challenge.
Braga-Ribas and his team discovered the rings while observing the way in that the asteroid blocked out light from a distant star as it passed between the star and Earth.
Piecing together results from telescopes at seven sites across South America, the team found narrow rings that were respectively seven and three kms wide.
The same technique was used to discover the rings around Uranus in 1977.
“Finding rings around Chariklo solves a puzzle about the object,” Braga-Ribas added.
A big question is how the rings can be stable, given the asteroid’s tiny mass.
If an impact caused them, it would have to have occurred at very low speed for the particles to remain in the centaur’s orbit.
“I think there is a good chance we would see another ring system around a small body somewhere in the outer Solar System,” Braga-Ribas said in a report published in Nature1.
Rings are interesting celestial features, as they are often a first step in the formation of planets and moons.