The James Webb Space Telescope revealed that the rings of Chariklo, a small asteroid between Saturn and Uranus, are changing in opacity, challenging assumptions about the stability of ring systems around minor solar system bodies.
The James Webb Space Telescope (JWST) has uncovered dramatic changes in the ring system of Chariklo, a small asteroid orbiting the sun between Saturn and Uranus.
The Discovery of Shifting Rings
Chariklo, a Centaur asteroid roughly 250 kilometers in diameter, was first found to have rings in 2013. But JWST’s observations in October 2022, using a technique called stellar occultation, showed that the rings have undergone significant changes over the past decade. By measuring how light from a distant star dimmed as Chariklo passed in front of it, researchers detected opposite trends: the inner ring became more opaque, while the outer ring grew less so.
By comparing JWST observations with those obtained during other stellar occultations over the last decade, we discovered opposite changes in the two rings,
said Pablo Santos-Sanz of the Institute of Astrophysics of Andalusia (IAA-CSIC), lead researcher on the study. Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability.
The Role of Stellar Occultation
The technique of stellar occultation, which tracks how light from a star is blocked by an object, was critical to this discovery. Chariklo’s rings are too faint to be directly imaged by JWST, but the telescope’s sensitivity allowed researchers to measure subtle variations in light as the asteroid passed in front of a star. This method also required precise knowledge of Chariklo’s orbit, the star’s position, and JWST’s trajectory around the L2 Lagrange point—a region of space about 1.5 million kilometers from Earth.
Achieving this required knowing with extraordinary precision the orbit of Chariklo, the position of the star, thanks to the European Space Agency’s Gaia mission, and the trajectory of JWST itself around the L2 Lagrange point,
said team member Yücel Kilic of IAA-CSIC. The JWST follows an orbit around this region that requires periodic corrections through station-keeping maneuvers.
Implications for Ring System Research
The findings have broader implications for understanding ring systems across the solar system. While Saturn’s rings are well-studied, smaller bodies like Chariklo and Chiron—another Centaur with rings—show that even tiny objects can host complex ring structures.
The ability to detect these changes opens a new window for understanding the evolution of these systems and, possibly, that of other ring systems in the solar system,
Santos-Sanz said.
What This Means for Future Exploration
This discovery underscores JWST’s capability to study distant, fast-moving objects with unprecedented precision. The telescope’s infrared instruments and sensitivity to subtle light variations allowed researchers to track changes in Chariklo’s rings despite the asteroid’s small size and distance—around 17 times Earth’s distance from the sun.
As researchers continue to analyze data from JWST, the study of Chariklo’s rings may provide clues about the formation and longevity of ring systems, including those around planets like Saturn and Uranus. For now, the findings remind scientists that even the smallest celestial bodies can harbor mysteries that challenge our understanding of the solar system.
