Rings aren’t exclusive to giant planets: Chariklo, an icy body only about 250 kilometres across—shorter than Tasmania is long—carries two narrow rings, and Webb observations suggest they are changing on timescales of years.

Chariklo is an unlikely place to look for a ring system. The icy Centaur is about 250 kilometres across, smaller than the roughly 286-kilometre length given for Tasmania in a Tasmanian government fact sheet. Yet two narrow rings orbit well beyond its surface.

A paper published in Science Advances on 9 September 2026 reports that those rings may be changing over timescales measured in years. A Webb occultation observed in 2022 found the dense inner ring about 50 per cent more opaque than earlier measurements, while the outer ring appeared about 60 per cent less opaque than it did in 2017. Their radial positions were essentially unchanged.

This is one study, not settled consensus. Webb observed in the near-infrared, whereas many earlier measurements were made at visible wavelengths. Some of the contrast could therefore reflect how very small grains interact with different colours of light rather than material physically appearing or disappearing.

The first small body known to have rings

Chariklo belongs to the Centaurs, a population of icy bodies on unstable orbits among the giant planets. Its rings were discovered during a 2013 stellar occultation, when astronomers watched it pass in front of a distant star.

The star briefly dimmed before and after Chariklo itself crossed the line of sight. The symmetric pattern revealed two rings, a result reported in Nature in 2014. It overturned the assumption that rings belonged only to giant planets.

The inner ring, C1R, is the denser component and is approximately six to seven kilometres wide. The outer C2R ring is only about two to four kilometres wide. They orbit roughly 390 and 405 kilometres from Chariklo’s centre, separated by a gap near nine kilometres.

Webb watched a star pass behind the rings

On 18 October 2022, Webb’s Near-Infrared Camera monitored the star Gaia DR3 6873519665992128512 as Chariklo passed close to it. From Webb’s viewpoint the body itself missed the star by only about 7.4 kilometres above its surface, while the rings crossed the line of sight.

The event was observed simultaneously through filters centred near 1.5 and 3.2 micrometres. Of 14,827 exposures, the analysis concentrated on 1,646 images around the predicted occultation. The inner ring produced clear drops in starlight and diffraction features marking sharp edges. The outer ring was only marginally detected at 1.5 micrometres and not detected at 3.2 micrometres.

NASA described the successful observation in 2023, when the analysis was still in progress. Space Daily also reported how Webb had captured Chariklo’s ring system. The newly published paper turns that technical success into a comparison across nearly a decade of occultation records.

The two rings seem to be moving in opposite directions

The 2026 study compared Webb’s data with occultations from 2013, 2014 and 2017. It found that C1R blocked more starlight than before, while C2R blocked much less. Models suggested it was unlikely that Webb had simply sampled an unusually dense part of one ring and an unusually sparse part of the other.

The Paris Observatory’s account of the paper summarised the change as an increase of about 50 per cent in the inner ring’s opacity and a decrease of about 60 per cent in the outer ring’s opacity compared with 2017.

Opacity is not a direct weighing of the rings. It measures how strongly ring material blocks the background star. A ring can become more opaque because it contains more material, because collisions have broken larger pieces into more light-blocking grains, or because a different wavelength interacts differently with the same particles.

A fading ring is only one interpretation

If the outer ring has truly lost opacity over five years, it may be dispersing. The paper estimated a median spreading timescale of only 0.36 years without some form of confinement or replenishment, with a one-sigma range from 0.23 to 0.77 years. The fact that C2R has remained near the same radius since its discovery implies that another process is helping maintain it.

A second explanation is wavelength dependence. Models could reproduce the weak infrared signature if C2R is dominated by silicate grains about 0.2 to 0.5 micrometres across. Such grains can block visible light efficiently while becoming much less apparent at Webb’s wavelengths.

The scenarios are not mutually exclusive. The ring could be dusty and evolving. A future visible-light occultation can test the distinction. If C2R again looks as opaque as it did in earlier visible observations, grain optics become the stronger explanation. If it remains faint, real material loss becomes harder to avoid.

Small rings may need continuous maintenance

The inner ring presents the opposite question. Its stronger opacity is difficult to explain through wavelength effects alone. It may have received new material, or collisions among larger particles may have produced a cloud of smaller grains with more total cross-section.

How either ring remains narrow is unresolved. Proposed explanations include small shepherd moons, resonances linked to Chariklo’s irregular shape, and repeated collisions. Space Daily covered one family of impact models in its report on the possible origin of minor-planet rings.

The most consequential part of the new result is not that the two ring radii moved. They did not, within the measurements. It is that apparently fixed architecture may hide rapid exchanges of dust and debris.

One occultation cannot finish the story

Webb cannot photograph these rings as resolved bands around Chariklo. The system is too small and distant. Instead, astronomers infer its structure from the brief shadows cast when the rings pass in front of a star.

That method is exceptionally sensitive, but each occultation samples particular ring segments at particular wavelengths. The team’s probability modelling argues against local density variations as the sole explanation, yet only repeated observations can separate a temporal trend from particle-size effects with confidence.

Chariklo first showed that a 250-kilometre body can possess rings. The 2026 evidence now suggests those rings are active structures, not merely miniature copies of a static planetary ornament.