New observations from the James Webb Space Telescope have revealed unexpected changes in the faint rings surrounding Chariklo, a small body classified as a centaur orbiting between Saturn and Uranus. Rings around Chariklo were first detected in 2013, and follow-up occultation studies were carried out in 2014 and 2017. The most recent dataset, obtained by JWST during a carefully timed stellar occultation in 2022 and analysed in a paper published on Sept. 9 in Science Advances, shows notable differences from the earlier measurements.
The JWST observations indicate that the inner ring has become more opaque while the outer ring appears to have decreased in opacity compared with the previous decade of occultation records. The study authors propose three non-exclusive explanations: the telescope’s higher resolution may have sampled denser and sparser ring regions that ground-based campaigns missed; the physical properties of ring particles could have altered over time; or scattering and absorption that depend on wavelength reveal grain-size or compositional differences now detectable in the infrared. Pablo Santos-Sanz, identified as the study’s lead author, and the team at the Institute of Astrophysics of Andalusia present these scenarios without asserting a definitive cause.
These results relied on a JWST campaign timed to an occultation, a technique necessary because Chariklo’s rings are too faint for direct imaging. To schedule the observation the team used star positions from the European Space Agency’s Gaia mission and precise knowledge of JWST’s orbit roughly 930,000 miles (1.5 million kilometres) from Earth. Chariklo’s relative sky motion during the event — about 1.5 miles per second (2.5 km/s) — allowed fine temporal sampling, but the effort required highly accurate timing and trajectory calculations.
Researchers stress that additional occultations will be essential to distinguish between true temporal evolution of the rings and effects that vary with observing wavelength. Confirmation from future events would clarify how ring systems can form and persist around small, distant bodies, and whether such systems are more dynamic than previously assumed. Until more data are collected, Chariklo’s changing rings offer a rare window into small-body ring physics and the limits of remote sensing techniques in the outer Solar System.
