Until just over a decade ago, ring systems were thought to be exclusive to the giant planets of the Solar System , such as Jupiter, Saturn, Uranus, and Neptune. However, in 2013, a small body, barely 250 kilometers in diameter and located almost 17 times the distance between the Earth and the Sun, joined this select group. This is Chariklo, a minor body orbiting between Saturn and Uranus, around which two dense rings were discovered.

On October 18, 2022, the Institute of Astrophysics of Andalusia (IAA-CSIC) led the observation with the James Webb Space Telescope (JWST) to study the rings of Chariklo using a stellar occultation, a technique that measures the decrease in a star's light when an object passes in front of it. Now, a new study published in Science Advances and also led by the IAA-CSIC demonstrates, for the first time, that the Chariklo ring system has undergone changes on timescales of just a few years. 

Schematic representation of the stellar occultation by the rings of Chariklo observed with the James Webb Space Telescope (JWST) on October 18, 2022. Comparison with previous occultations shows opposite changes in both rings: C1R exhibits a more intense signal, while C2R appears much fainter. Credit: Yücel Kılıç, Pablo Santos Sanz and Celia Navas (IAA-CSIC)

 

“Comparing the JWST observations with those obtained during other stellar occultations over the last decade has allowed us to discover opposite changes in the two rings: while the inner ring shows a significantly greater opacity, the outer one presents a lower opacity,” explains Pablo Santos-Sanz, IAA-CSIC researcher who leads the study.

This unexpected behavior indicates that the Chariklo ring system is dynamic and that it may be subject to much more complex physical processes than previously thought.

 

A SCIENTIFIC AND TECHNOLOGICAL MILESTONE

The study also represents a significant technological advance: the occultation by Chariklo was the first stellar occultation predicted and planned specifically to be observed with the James Webb and successfully executed from this space telescope. 

“Achieving this required knowing with extraordinary precision the orbit of Chariklo, the position of the star—thanks to the ESA's Gaia mission—and the trajectory of the JWST itself around the L2 Lagrange point, a region of space located about 1.5 million kilometers from Earth in the opposite direction from the Sun. The JWST orbits around this region following a trajectory that must be periodically corrected through maintenance maneuvers,” explains Yücel Kilic, a postdoctoral researcher at the IAA-CSIC hired under the Severo Ochoa project and co-author of the study.

 

 

At the time of the occultation, Chariklo was moving relative to the JWST at just 2.5 kilometers per second. This exceptionally low relative speed allowed for unprecedented spatial resolution in studying the structure of its rings. These rings are so narrow, and Chariklo is so far away, that they cannot be photographed directly, even with the James Webb Space Telescope or the largest ground-based telescopes. Stellar occultations allow them to be studied indirectly, by measuring the brief dips in a star's brightness as each of the rings passes in front of it.

Until now, the rings surrounding small bodies in the Solar System were considered relatively stable structures. The changes detected in Chariklo challenge this view and suggest that these systems may be much more dynamic than previously thought. “Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability. 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,” says Santos-Sanz. The physical origin of the detected changes remains, however, an open question: they could reflect a temporal evolution of the rings, differences related to the use of different observation filters, or a combination of both effects.

The Institute of Astrophysics of Andalusia (IAA-CSIC) led all phases of the study, from the scientific design of the project and the prediction of the occultation by Chariklo observed by the JWST, to the data analysis and the physical interpretation of the results. The IAA-CSIC team also played a fundamental role in the modeling of the rings and in the statistical analysis that demonstrated that the detected changes are real. The work was carried out in collaboration with researchers from Spain, Brazil, France, Hungary, and the United States.

Quelle: Institute of Astrophysics of Andalusia – CSIC.