Why the 100-kilometer limit? Pan says that outgassing on smaller objects wouldn't have enough mass to stop the dusty material from flying away. She adds that Kuiper Belt objects wouldn't be expected to have these rings, because they're too far from the sun and thus too cold to experience this outgassing. Even if a Kuiper Belt object moved close enough to a planet to split a little orbiting moon apart, the trajectory would inevitably change the asteroid into a Centaur.
ANALYSIS: First Asteroid Found Sporting a Ring System
Observations of Chariklo are limited so far, but astronomers have seen that it has two rings. They are wider on one side of Chariklo than the other, with the second ring only containing about one-tenth the mass of the first ring.
Pan's team suggests that the ring is not quite circular (elliptical). The particles don't form into a circle due to the individual gravitational interactions between particles. The research implies that for this to happen, you would need to have enough material to create a 1-km (0.62-mile) sized ice ball. A typical particle would also have to be a few meters in size.
When comparing Chariklo's rings to other ringed bodies in the solar system, it appears most similar to Uranus despite its diminutive size.
"The geometry of Chariklo's rings, which are fairly dense and narrow, is most like that of the Uranian rings. Interestingly, some of the Uranian rings are also noticeably elliptical, and studies of the Uranian system inspired our treatment of Chariklo's rings," Pan wrote.
ANALYSIS: Baked Asteroids Suffer Fatigue and Fragment
Pan plans to next examine how the rings became eccentric in the first place. Some kind of perturbation must have forced them to become eccentric instead of circular, she says. She also is interested (more generally) in seeing if it's possible to predict a ring's eccentricity based on its mass and width.
Pan's research, which has been accepted in the Astrophysical Journal, is available in preprint version on Arxiv.