Astronomers have observed, for the first time, a ring system forming and evolving around 2060 Chiron — a small icy body orbiting between Saturn and Uranus.
Chiron is a centaur — an object that shares characteristics of both asteroids and comets — approximately 200 km in diameter and takes about 50 years to complete a full orbit around the Sun.
Using data collected from stellar occultation events spanning from 2011 through to 2023 — particularly from Brazil's Pico dos Dias Observatory — researchers identified four distinct ring- or disk-like features around Chiron: three relatively dense rings located roughly 270 km to 430 km from its center, and a fourth, more diffuse feature at approximately 1,400 km.
Lead author Chrystian Luciano Pereira of Brazil's National Observatory said, "This provides a rare glimpse into how such structures originate and change."
Meanwhile co-author Braga Ribas of the Federal University of Technology-Paraná added, "It is an evolving system that will help us understand the dynamical mechanisms governing the creation of rings and satellites around small bodies, with potential implications for various types of disk dynamics in the universe."
Unlike the stable and mature ring systems around giant planets such as Saturn, Chiron's rings appear to be actively forming and changing. That makes this discovery especially significant.
The possible origins for the material around Chiron include a shattered moon or debris from a collision and a comet-like outbursts from Chiron's surface that ejected dust and ice into orbit.
Intriguingly, the outermost feature lies beyond the Roche limit — the distance at which orbiting material typically clumps into a moon rather than remaining in a ring. Pereira remarked, "Beyond that limit, particles forming a ring should naturally begin to coalesce into a satellite – yet something seems to be preventing that from happening."
One explanation is that the system is so young it hasn't yet had time to form a moon, or that the particles are being continually replenished. A specialist at NASA Goddard Space Flight Center, Keighley Rockcliffe (not part of the study), commented, "Maybe it's recently formed and it hasn't had the chance to form a little centaur-let."
This discovery pushes our understanding of ring formation beyond giant planets and shows that smaller bodies in the Solar System can develop ring systems — and may do so actively. Chiron joins the small group of ringed minor-bodies (including 10199 Chariklo, Haumea and Quaoar) — but stands out as potentially the most dynamic of them.
By watching a ring system in formation, scientists can better investigate how disks of material — such as those that form moons, or even planetary rings — evolve. The physical mechanics of why material stays dispersed (and doesn't just clump into a body) are still being explored and could relate to ice vs. rock composition, gravitational resonances, or continual replenishment.
The team say that more occultation observations — where Chiron passes in front of distant stars and the drop in starlight is measured — will help determine changes in ring thickness, opacity and structure, confirming if the rings are truly evolving. Pereira noted, "The ideal scenario to satisfy our curiosity, however, would be a space mission dedicated to in-situ observation of this intriguing system."
In short, Chiron offers astronomers a front-row seat to watch the building blocks of celestial rings at work — an unprecedented window into the Solar System's ongoing dynamism.
