For the first time, astronomers are observing a ring system forming in real time around the comet-like object Chiron. This distant body, orbiting between Saturn and Uranus, shows changing rings with each observation. The discovery could reveal how such systems develop in the outer solar system.
Chiron, a comet-like object that follows a path around the sun between the orbits of Saturn and Uranus, has been caught in the act of developing new rings. Every observation of Chiron reveals slight differences in its ring structure, marking the first time scientists are witnessing such a formation process unfold live.
Rings around small solar system bodies are not unprecedented. The asteroid Chariklo and dwarf planets Haumea and Quaoar also possess small ring systems, all detected through stellar occultation—a technique that maps how an object's orbiting material blocks a distant star's light. "There are only maybe 20 objects that have been observed through stellar occultations, so observing four of them with rings is high statistics," says Bruno Sicardy at the Paris Observatory in France. He adds, "There are hundreds or thousands of bodies out there, so there must be hundreds of ring systems," predicting many more discoveries ahead.
Sicardy and his team analyzed data from a 2023 stellar occultation event. Prior studies had suggested three rings around Chiron, but this observation revealed an additional disc of material enveloping those rings and extending farther from Chiron's surface, along with a previously unseen ring even more distant.
"Nature is showing us a ring in the formation stage, which is very lucky for us, because when we look at Saturn’s rings or Uranus’s rings, or even Chariklo’s rings, they basically always stay the same," Sicardy notes. Observing this dynamic process offers insights into ring formation mechanisms. Team member Chrystian Pereira at the National Observatory of Brazil explains, "[This could] shed light on the specific conditions that allow the formation, persistence or dissipation of rings, and may ultimately explain why such systems are only found in the cold, icy regions of the solar system."
The findings appear in The Astrophysical Journal Letters (DOI: 10.3847/2041-8213/ae0b6d).