Located at some two billion kilometers from Earth, Chariklo is a “Centaur object,” belonging to a group of small bodies of the outer Solar System whose orbits lie between those of the giant planets. With a radius of about 125 km, it is the largest known Centaur.
In 2013, a ground-based stellar occultation - the passage of Chariklo in front of a distant star - led to the unexpected discovery of two narrow rings around this object: a discovery that would revolutionize our understanding of small bodies in the Solar System. Located approximately 390 and 405 km from Chariklo‘s center, the rings are only a few kilometers wide.
On October 18, 2022, an international team of scientists led by the Andalusian Institute of Astrophysics (IAA-CSIC) once again used this technique, but this time with the JWST. This was the first stellar occultation specifically planned and successfully observed with the James Webb Space Telescope. Thanks to its ability to observe in the near-infrared, up to about 5 micrometers, the JWST made it possible to study the rings at wavelengths previously inaccessible from the ground.
A striking aspect of the results is that the positions of the two rings are essentially unchanged, but their properties appear to have been modified. The inner ring, C1R, now appears about 50% more opaque than before. Conversely, the outer ring, C2R, exhibits a much weaker signal: its opacity appears to have decreased by about 60% compared to 2017.
These variations do not appear to be attributable simply to the fact that the JWST observed different portions of the rings. They instead indicate that an actual evolution of the system is taking place. For C2R, the decrease in opacity could reflect a gradual loss of material, while the increase in opacity of C1R could result from an influx of material or from the fact that collisions broke larger particles into a multitude of finer grains.
This new observation adds an important piece to the puzzle of the origin, stability, and evolution of Chariklo’s pocket rings.
Future occultations, particularly in the visible spectrum, will make it possible to determine whether the observed changes are continuing and to definitively establish whether they represent a temporal evolution or are effects related to wavelength.
Reference
This work is the topic of an article entitled “JWST stellar occultation reveals unexpected changes in Chariklo’s ring system”, by Pablo Santos-Sanz et al., published in Science Advances, on September 9, 2026.
DOI : https://doi.org/10.1126/sciadv.aeh4794
It has been partly developed in the framework of the ANR project "Roche" (ANR-23-CE49-0012) at the “Laboratoire Temps Espace“ of Paris Observatory - PSL. This project aims at better understanding the environment and the interactions of small bodies of the Solar system. It is also part of the ERC project "Lucky Star" (2015-2021) dedicated to stellar occultations and gathering teams from France, Spain and Brazil.