Cool science news of the week: astronomers have discovered a ring system surrounding an asteroid — the first of its kind known in the Solar System. The asteroid, Chariklo, orbits the Sun between the orbit of Saturn and the orbit of Uranus. Chariklo is about 250 km in diameter (although not quite truly spherical, as far as scientists can tell so far), making it the largest of the known asteroids that orbit between Jupiter and Neptune.
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.
There are only four other known ring systems in our solar system — around Jupiter, Uranus, Neptune and, most dramatically, Saturn — and all the other ones have formed around planets. Astronomers aren’t yet sure if Chariklo’s ring system makes it unique among asteroids. In recent decades, more than 10 other objects in its neighborhood have been searched using a technique similar to Chariklo’s stellar eclipse but have not shown any rings.