How a Tiny Body’s Rings Changed Over the Past Decade

For a long time, the cosmic rulebook suggested that planetary rings were an exclusive feature of massive gas giants. That assumption shattered in 2013 when astronomers observed a stellar occultation involving a small, dark object orbiting between Saturn and Uranus. The starlight flickered twice before and after the primary dimming, exposing two narrow bands encircling a world only about 250 kilometers wide. “It was a surprise,” says Pablo Santos-Sanz, an astronomer at the Instituto de Astrofísica de Andalucía in Granada, Spain. Since that discovery, researchers have been eager to determine the composition of these rings and understand their longevity.

A new study led by Santos-Sanz utilized the James Webb Space Telescope to monitor the same object, now identified as Chariklo, during another stellar pass. The data revealed a dramatic transformation: one ring had become significantly denser while the other had nearly disappeared. The underlying cause for this volatility remains unknown.

The observational method relies on precise timing and geometry. “We predict when a Solar System object passes in front of a star,” Santos-Sanz explained. As the object moves across the star’s face, the resulting dip in brightness provides critical data on the target’s dimensions and surrounding structures. He noted that this process is “particularly challenging for minor bodies, and more challenging for distant minor bodies.” The challenge stems from the tiny angular size of the target against the sky and the need for exact orbital coordinates for both the object and the background star. Despite these hurdles, ground-based telescopes successfully mapped Chariklo’s initial ring system in 2013. These features, designated C1R and C2R, orbited at distances of 390 and 405 kilometers from the center respectively. Each band was merely a few kilometers wide with a gap of approximately 7 kilometers separating them.