Plate Nº 59 · recorded October 10, 2026
Space & AstronomyReported finding
Webb Telescope Spots Unexpected Shifts in Chariklo's Rings Over Just a Few Years
JWST data show Chariklo's inner ring grew more opaque while its outer ring grew less opaque in a few years, challenging assumptions about the stability of small-body ring systems.
By Marcus Bennett3 min read621 words
In brief
- JWST observed Chariklo during a stellar occultation on October 18, 2022, the first such event planned specifically for the telescope.
- Chariklo is roughly 250 kilometers across and orbits about 17 times farther from the Sun than Earth, between the paths of Saturn and Uranus.
- Compared with observations from the previous decade, the inner ring showed higher opacity and the outer ring showed lower opacity.
- The relative motion between Chariklo and JWST during the occultation was only 2.5 kilometers per second, allowing unusually fine spatial reconstruction.
- The study, led by IAA-CSIC, was published in Science Advances on September 15, 2026 (DOI: 10.1126/sciadv.aeh4794).
Chariklo's two rings changed in measurable ways in less than a decade. New observations from the James Webb Space Telescope (JWST), published in Science Advances on September 15, 2026, show the inner ring grew more opaque while the outer ring grew less opaque.
Chariklo is a small, roughly 250-kilometer-wide object about 17 times farther from the Sun than Earth. It travels between the orbits of Saturn and Uranus. In 2013, astronomers discovered two dense rings circling it, the first rings ever seen around a small Solar System object.
"By comparing JWST observations with those obtained during other stellar occultations over the last decade, we discovered opposite changes in the two rings: while the inner ring shows significantly higher opacity, the outer ring shows lower opacity," said Pablo Santos-Sanz, the study's lead author and a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) in Spain.
How do astronomers measure rings that no telescope can image?
The key observation occurred on October 18, 2022. JWST watched Chariklo briefly pass in front of a distant star, an event called a stellar occultation. As Chariklo and its rings crossed the line of sight, they blocked tiny slivers of starlight for fractions of a second.
Each dip in brightness reveals the width, density, and structure of whatever crossed the star's path. Direct imaging was not an option. Chariklo sits too far away and its rings are too narrow for any current telescope, including JWST, to resolve.
A rare advantage came from geometry. As the occultation unfolded, Chariklo moved relative to JWST at only 2.5 kilometers per second. That unusually slow relative speed let researchers reconstruct spatial details with high precision.
What did it take to point JWST at the right pixel?
The observation marked the first time astronomers specifically predicted a stellar occultation for JWST and successfully carried it out. Doing so required knowing three positions to extreme accuracy: the orbit of Chariklo, the location of the background star, and JWST's path around the L2 Lagrange point, a gravitationally stable region about 1.5 million kilometers from Earth.
ESA's Gaia mission supplied the precise stellar position. "Achieving this required knowing with extraordinary precision the orbit of Chariklo, the position of the star — thanks to ESA's Gaia mission — and the trajectory of JWST itself around the L2 Lagrange point," said Yücel Kilic, a postdoctoral researcher at IAA-CSIC and co-author. JWST relies on periodic station-keeping maneuvers to remain in that orbit.
What could be causing the changes?
The team compared the 2022 JWST data with occultation observations collected over the previous decade. The opposite opacity shifts, more blockage by the inner ring and less by the outer, emerged consistently from statistical tests.
Exactly why remains uncertain. Three possibilities stand out:
- Genuine physical evolution inside Chariklo's rings, possibly driven by particle collisions, gravitational nudges from unseen shepherd moons, or dust interactions
- Differences introduced by the filters used on different telescopes during different occultations
- Some combination of both effects
The authors acknowledge they cannot yet separate these factors.
What does this mean for ring systems around small worlds?
Until now, astronomers largely treated rings around small bodies as stable, long-lived features. Chariklo's shifting rings suggest otherwise.
"Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability," Santos-Sanz said. "The ability to detect these changes opens a new window for understanding the evolution of these systems."
The IAA-CSIC team led the project end to end: predicting the occultation, securing JWST time, analyzing the photometric data, and modeling the ring structures. Collaborators from Brazil, France, Hungary, and the United States contributed to the analysis.
via dx.doi.org (Original)
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