A small world beyond Saturn is giving astronomers a fresh puzzle about planetary rings. Observations from the James Webb Space Telescope show that Chariklo\u2019s inner ring blocks more starlight than earlier measurements suggested, while its outer ring produces a much weaker signal.<\/p>\n\n\n\n
The findings, published September 9, 2026, suggest that rings around small objects can change over just a few years. But there is a twist worth keeping in mind before imagining a ring disappearing into space. Some of the difference may come from how the particles interact with the infrared light Webb observes.<\/p>\n\n\n\n
Chariklo measures about 155 miles (250 kilometers) across and travels around the sun between Saturn and Uranus. It belongs to a population of small outer solar system bodies<\/a> called centaurs, and astronomers discovered its two narrow rings in 2013.<\/p>\n\n\n\n According to the Paris Observatory<\/a>, the inner ring, known as C1R, appeared roughly 50% more opaque than in previous observations. The outer ring, C2R, showed an apparent opacity decrease of about 60% compared with 2017, even though both rings remained at essentially the same distances from Chariklo\u2019s center.<\/p>\n\n\n\n What does \u201copacity\u201d mean here? Simply put, it describes how effectively the ring material blocks the background star\u2019s light. Those percentages describe differences in light blocking, so they should not be read as equivalent changes in the rings\u2019 mass.<\/p>\n\n\n\n The key observation took place on October 18, 2022, when Chariklo\u2019s rings crossed in front of a distant star from Webb\u2019s viewpoint. The telescope\u2019s Near-Infrared Camera recorded brief dips in brightness, a technique called stellar occultation<\/a>. Chariklo\u2019s solid body missed the star from that viewing angle, but its rings did not.<\/p>\n\n\n\n Think of watching a porch light through a passing screen. Even if you cannot make out every strand, changes in the light can reveal something about what is crossing your view. Astronomers use the timing and depth of these stellar dimmings to investigate distant rings.<\/p>\n\n\n\n That indirect approach matters because Chariklo\u2019s rings are too narrow and too far away for Webb to photograph separately from the body itself. Instead of a crisp picture like the familiar images of Saturn, researchers work with a graph showing how the star\u2019s brightness changes over time<\/a>. A small dip carries a surprising amount of information.<\/p>\n\n\n\n The team, led by Pablo Santos-Sanz at Spain\u2019s Institute of Astrophysics of Andalusia<\/a> (IAA-CSIC), considered several explanations for the differences. Material could have entered the inner ring, or collisions could have broken larger particles into smaller grains<\/a>, increasing the area available to block starlight.<\/p>\n\n\n\n For the outer ring, a weaker signal could point to material being lost. But Webb observed in near-infrared light, while earlier comparison observations were mostly made in visible light, and small particles can interact differently with different wavelengths. That leaves room for more than one explanation, including a combination of physical evolution and wavelength effects.<\/p>\n\n\n\n \u201cOur results force us to rethink how they form, how they evolve, and what mechanisms ensure their stability,\u201d Santos-Sanz said in an official release. The measurements raise questions about how such narrow rings survive, but the physical cause of the changes remains unresolved.<\/p>\n\n\n\n Catching the event required accurate predictions of Chariklo\u2019s path, the background star\u2019s position and Webb\u2019s own movement. The European Space Agency\u2019s Gaia mission supplied precise stellar position data, while researchers also accounted for Webb\u2019s orbit around the L2 region, roughly 930,000 miles (1.5 million kilometers) from Earth.<\/p>\n\n\n\n During the occultation, Chariklo moved relative to Webb at about 1.6 miles per second (2.5 kilometers per second), or roughly 5,600 mph. That sounds fast enough to make highway traffic seem motionless, but it was unusually slow for this kind of observation. The slower crossing helped researchers examine finer details in the rings\u2019 structure.<\/p>\n\n\n\n Future stellar occultations<\/a>, especially measurements in visible light, could help separate changes over time from differences caused by observing wavelength. They could also show whether the outer ring\u2019s weaker signal persists and whether the inner ring continues to block more light.<\/p>\n\n\n\n For readers, the distinction is straightforward. Webb has revealed meaningful differences in the rings\u2019 signals, while the explanation still needs testing. That makes Chariklo a useful place to investigate how rings around small worlds evolve.<\/p>\n\n\n\n The next well-timed crossing of a distant star could help clarify the picture. The study was published in Science Advances<\/a>.<\/p>\n\n\n\n Photo: L. Maquet, Observatoire de Paris<\/p>\n","protected":false},"excerpt":{"rendered":" A small world beyond Saturn is giving astronomers a fresh puzzle about planetary rings. Observations from the James Webb Space … <\/p>\nHow Webb studied rings it cannot photograph<\/h2>\n\n\n\n
Why darker does not always mean heavier<\/h2>\n\n\n\n
A carefully timed observation in deep space<\/h2>\n\n\n\n
What comes next for Chariklo<\/h2>\n\n\n\n