According to new observations from the James Webb Space Telescope (JWST), the ring system surrounding Chariklo, a small centaur object orbiting between Saturn and Uranus, appears significantly different than it did in previous studies. Chariklo, a rare type of solar system body that exhibits traits of both asteroids and comets, spans approximately 400 miles (250 kilometers) in diameter. It was the first small solar system body found to possess rings, discovered in 2013 and subsequently observed via ground-based telescopes in 2014 and 2017.
A study published on September 9 in the journal Science Advances highlights the contrast between those earlier views and JWST’s 2022 observations. Researchers noted a decade of transformation in the ring structure. Pablo Santos-Sanz, a researcher at the Institute of Astrophysics of Andalusia and lead author of the study, stated that comparisons revealed opposite changes in the two rings: while the inner ring demonstrated significantly higher opacity, the outer ring appeared less opaque.
The authors proposed three potential explanations for these shifts. First, JWST’s superior resolution may have revealed denser and sparser zones within the rings that previous instruments could not detect. Second, the material composition or grain structure of the rings may have physically changed. A third possibility is that the telescope captured grains with optical properties dependent on wavelength, allowing scientists to observe variations in composition and grain size that account for the apparent opacity changes.
Santos-Sanz emphasized that these findings suggest small, ringed bodies in the distant solar system are more dynamic than previously assumed, even when far from a planet’s gravitational influence. “Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability,” he said. The researchers added that future theoretical observations during the next stellar occultation—when Chariklo passes in front of a star—would help confirm whether the changes are temporal or due to scattering effects.
These observations also mark a milestone for JWST as the first instance where scientists planned a viewing campaign specifically timed around a stellar occultation. Because Chariklo’s rings are too faint for direct imaging, astronomers must rely on measuring brightness fluctuations as the object transits a background star, a technique similar to studying exoplanet atmospheres. Chariklo’s low relative speed of 1.5 miles per second (2.5 kilometers per second) facilitated high-resolution imaging. To achieve the necessary timing precision, researchers utilized data from the European Space Agency’s Gaia mission, which maps over 2 billion stars, alongside calculations of JWST’s position roughly 930,000 miles (1.5 million kilometers) from Earth.
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