In October 2022, Spanish astronomers used NASA's James Webb Space Telescope to study the rings of the celestial object known as 10199 Chariklo, located in the outer Solar System. Chariklo, classified as a centaur, orbits the Sun between Jupiter and Neptune and intersects the orbits of some giant planets. These objects are characterized by unstable orbits that are expected to last only a few million years.
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Since its discovery in 1997, Chariklo has piqued interest, especially after observations during a stellar occultation in 2013 revealed it has a pair of dense rings, making it the second smallest known object with such features; the smallest is another centaur, Chiron. Prior to these findings, only the gas giants were believed to have ring systems, challenging previous understandings of astronomical structure and encouraging further studies of ringed centaurs.
On October 18, 2022, researchers from the Institute of Astrophysics of Andalusia (IAA-CSIC) monitored Chariklo's rings during a stellar occultation, leading to new insights published in Science Advances. Their analysis indicated that significant changes in the rings had occurred over recent years, pointing to a more dynamic system than previously thought.
Lead researcher Pablo Santos-Sanz noted that observations from four years prior showed contrasting changes in the rings. The inner ring exhibited increased opacity, while the outer ring's opacity decreased. This disparity may indicate that Chariklo's ring system is affected by a wider range of processes than astronomers had anticipated.
This observation marks a significant milestone as it was the first stellar occultation successfully predicted and observed with the Webb telescope. Study co-author Yücel Kilic highlighted the precision needed in tracking Chariklo's orbit, the position of the star—facilitated by ESA's Gaia mission—and JWST's trajectory, approximately 1.5 million kilometers from Earth.
The 2022 occultation saw Chariklo moving at approximately 2.5 kilometers per second relative to Webb, an ideal speed for observing the rings. Given the rings' narrow width and their distance from Earth, traditional imaging methods are challenging, necessitating stellar occultations to indirectly study these features by monitoring changes in starlight.
As the team continues to investigate, questions remain about the mechanisms driving the changes in Chariklo's rings. Santos-Sanz remarked that these findings compel a reevaluation of how rings form, evolve, and maintain stability, potentially enhancing understanding of other ring systems in the Solar System. The study titled "JWST stellar occultation reveals unexpected changes in Chariklo’s ring system" was published in Science Advances.