Astronomers using the James Webb Space Telescope discovered that Chariklo, an icy body measuring about 250 kilometres across, carries two narrow rings that are actively changing on timescales of years. Published in September 2026, the findings reveal opposite shifts in opacity between the inner and outer rings.
Rings were once considered the exclusive domain of giant planets like Saturn, Uranus, Neptune, and Jupiter. That assumption broke down when astronomers detected two narrow rings orbiting Chariklo, a tiny icy object belonging to the Centaur population. These objects travel on unstable orbits among the giant planets, situated around 17 times the distance between Earth and the sun.
Now, new observations captured by the James Webb Space Telescope are upending what scientists thought they knew about how these delicate structures behave. Rather than remaining static, the rings of this small body appear to be changing over timescales measured in years.
Stellar Occultation and the Webb Telescope
Because Chariklo and its rings are far too small and distant for direct imaging, even with advanced observatories, researchers rely on a technique called stellar occultation. This method measures the precise dip in light from a background star when an object passes directly in front of it. On October 18, 2022, the Webb telescope monitored the star Gaia DR3 6873519665992128512 as the asteroid passed close by, with the rings crossing the line of sight while the main body missed the star by a narrow margin.
The effort required extraordinary precision. Teams had to account for the orbit of Chariklo, the position of the star provided by the European Space Agency’s Gaia mission, and the trajectory of the Webb telescope itself around the L2 Lagrange point located about 1 million miles beyond Earth. The observatory follows an orbit around this region that requires periodic station-keeping maneuvers.
Opposite Shifts in the Inner and Outer Rings
By comparing the Webb data from 2022 with historical occultation records from 2013, 2014, and 2017, researchers discovered that the two rings are behaving in starkly contrasting ways. The dense inner ring, designated C1R and measuring roughly six to seven kilometres wide, showed an increase in opacity. Meanwhile, the outer ring, C2R, which spans only about two to four kilometres wide, showed a significant drop in opacity compared to earlier measurements.
According to accounts of the paper from the Paris Observatory, the analysis pointed to 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 to 2017 levels. Radial positions for both rings remained essentially unchanged.
Evaluating Material Loss Versus Grain Optics
Opacity measures how strongly ring material blocks background starlight rather than providing a direct weighing of the mass. A ring can alter its opacity because it has gained or lost material, because collisions have shattered larger fragments into smaller light-blocking grains, or because different wavelengths interact differently with specific particles.
If the outer ring is genuinely losing material, models estimate a median spreading timescale of only 0.36 years unless confinement or replenishment mechanisms maintain it. Alternatively, some models suggest the weak infrared signature could be reproduced if the outer ring is dominated by silicate grains roughly 0.2 to 0.5 micrometres across. Such particles block visible light efficiently while becoming far less apparent at the near-infrared wavelengths observed by Webb.
Reassessing Small Body Ring Dynamics
The findings challenge long-held assumptions that ring systems around small bodies maintain long-term stability. The inner ring’s stronger opacity is difficult to explain through wavelength effects alone, pointing instead to potential new material inputs or collision-driven pulverization.
Future visible-light occultations will test whether grain optics or actual physical dispersion drive the observed changes in the outer ring. Until then, the active evolution documented across nearly a decade of records demonstrates that small body ring systems are far more dynamic than previously understood.
