Source: http://www.wired.com/wiredscience/2014/0...

For the first time ever, astronomers have discovered a ring system surrounding an asteroid. The finding is a complete surprise to planetary scientists, who are yet unsure exactly how such rings could have formed.

The cosmic bling was found around an object named Chariklo, which orbits in a region between Saturn and Uranus. At 155 miles across, or about the length of Massachusetts, Chariklo is the largest known asteroid in its neighborhood. Looking to get a better idea of its exact size and shape, astronomers trained their telescopes on the giant space rock as it passed in front on a distant star in June 2013. As Chariklo performed its eclipse, researchers noticed something odd: The star’s light flickered just a bit immediately before and after Chariklo’s pass.

The reason for this darkening was the asteroid’s two dense rings, which had briefly blocked the starlight. The thicker inner ring is about four miles wide, while the thinner outer ring is a little less than two miles. Spectroscopic analysis of the starlight also revealed that the rings are composed partially of water ice.

The ice rings reflect light like a mirror, a property that helps explain an earlier anomalous finding regarding Chariklo. After the asteroid was discovered in 1997, its brightness mysteriously dropped off and only came back again in 2008. What apparently happened was that, as Chariklo moved through its orbit, its ring system turned edge-on when viewed from Earth. As they turned back to face us with their flat side, they reflected light toward our planet and Chariklo’s brightness grew by 40 percent.