A small icy world orbiting between Saturn and Uranus is offering astronomers a new perspective on how rings can evolve. Chariklo, a Centaur measuring about 250 kilometres across, is surrounded by two narrow rings--an unusual feature first identified in 2013.
New observations from the James Webb Space Telescope suggest that these rings are not static. The denser inner ring, known as C1R, appears to have become significantly more opaque over recent years, while the fainter outer ring, C2R, has weakened.
A precise stellar alignment
Webb examined Chariklo during a 2022 stellar occultation, when the object and its rings briefly passed in front of a distant star. Although the telescope cannot directly resolve the rings, the subtle changes in starlight provided a highly detailed measurement of their structure.
The analysis found that C1R's equivalent width--a measure combining ring density and apparent breadth--increased by around 50% compared with earlier observations. Meanwhile, C2R showed an equivalent width roughly 60% lower than measurements recorded in 2017.
Researchers say a simple transfer of material between the rings is unlikely, as the inner ring's rise is far greater than the outer ring's apparent loss. One possibility is that collisions between larger particles created fine debris, making C1R more effective at blocking light. The outer ring may be losing small grains as solar radiation gradually alters their orbits.
Clues to ring formation
A small, as-yet-undetected moonlet may also help confine or replenish Chariklo's rings. Such "shepherd" bodies are known to shape ring structures around larger planets and could play a similar role around smaller Solar System objects.
The findings, published in Science Advances, add to growing evidence that rings can form and change around worlds beyond the giant planets. Chariklo joins other small bodies, including Haumea and Quaoar, known to host ring systems.
Future occultation observations at visible wavelengths could clarify how particle size and composition influence the changing signals. Chariklo's evolving rings may help scientists build a broader model of how planetary rings emerge, persist and transform across the Solar System.
This research opens a promising path toward understanding dynamic ring environments around even the smallest worlds.
