Saturn’s magnificent rings have been known since Galileo observed the planet’s “ears” in his telescope. In the last few decades, researchers found rings (albeit less shiny ones) around the other giant planets — Jupiter, Uranus, and Neptune. And now the small asteroid Chariklo has joined the ring cycle: observations revealed it has two narrow rings, probably composed of water ice. It’s an intriguing discovery, since nothing else we’ve found at intermediate sizes has rings, leading to questions of how they form, how stable they may be, and whether there might be other beringed objects out there.

Beyond size, another challenge is Chariklo’s location between Saturn and Uranus. It orbits in a long ellipse, ranging from 13 to nearly 19 times farther from the Sun than Earth. This position, along with its composition of rock and ice, marks Chariklo as a “centaur.” Just like mythological centaurs are half human and half horse, astronomical centaurs combine features of asteroids and comets. (Centaurs would grow comet-like tails if they fell closer toward the Sun.) Tens of thousands of centaurs may lurk among the giant planets, though most of those are much smaller than Chariklo, the largest known centaur. [Read more…]