Though Saturn’s rings are the most famous, there are actually five known ringed bodies in the solar system: Uranus, Neptune, Jupiter and a centaur known as Chariklo. Now, scientists are looking to add a sixth body to the pantheon of ringed objects: Chiron, yet another centaur.
Centaurs are rocky, so-called “minor planets” that possess qualities of both asteroids and comets. Scientists only recently detected Chariklo’s ring system, and the finding was surprising – centaurs were thought to be mostly dormant. After observing Chiron pass in front of a bright star in 2011, the shadows and other optical features revealed by blocking the star’s light indicate that Chiron, too, might be the proud owner of a ring system.
“It’s interesting, because Chiron is a centaur—part of that middle section of the solar system, between Jupiter and Pluto, where we originally weren’t thinking things would be active, but it’s turning out things are quite active,” says Amanda Bosh, a lecturer in MIT’s Department of Earth, Atmospheric and Planetary Sciences.
Chiron was first discovered in 1977, and is believed to be one of some 44,000 centaurs in the solar system. In 1993 and 1994, an MIT scientist named James Elliot first estimated Chiron’s size, and also observed it exhibiting comet-like behavior – jets of water and dust spewing from the surface. This was the first indication that Chiron (and perhaps other centaurs) weren’t as dormant as once thought.
By charting its orbit, researchers calculated that Chiron would pass in front of a star on Nov. 29, 2011, and made arrangements to have access to telescopes. Still, even with that certainty, the team had to be diligent in their observation.
“There’s an aspect of serendipity to these observations,” Bosh says. “We need a certain amount of luck, waiting for Chiron to pass in front of a star that is bright enough. Chiron itself is small enough that the event is very short; if you blink, you might miss it.”
Though a solid body would create a predictable pattern when blocking the star’s light, the researchers noticed symmetrical, sharp features about 300 km from Chiron, at the beginning and end of the event. Such unusual features indicate that dust may be partially blocking some of the light as well. While it’s possible that Chiron has symmetrical dust and/or gas jets, the observations could also indicate a ring or shell of dust surrounding the centaur.
Such a scenario, however unlikely it may be, isn’t impossible. Centaurs have gravity just like everything else in the universe, and if another body of some sort were to break up, it’s possible that the resulting debris could get stuck in Chiron’s gravitational pull. Though an independent group has combined their findings with MIT’s and reached the same conclusion that Chiron has rings, more event observations are necessary for confirmation.
“If we want to make a strong case for rings around Chiron, we’ll need observations by multiple observers, distributed over a few hundred kilometers, so that we can map the ring geometry,” says Jessica Ruprecht, a researcher at MIT. “But that alone doesn’t tell us if the rings are a temporary feature of Chiron, or a more permanent one. There’s a lot of work that needs to be done.”