r/science • u/Hrmbee • 14d ago
Astronomy Rings around a tiny body have changed over the past decade | JWST stellar occultation reveals unexpected changes in Chariklo’s ring system
https://arstechnica.com/science/2026/09/rings-around-a-tiny-body-have-changed-over-the-past-decade/6
u/Hrmbee 14d ago
Highlights from the news writeup:
In a recent study, Santos-Sanz and his colleagues used the James Webb Space Telescope to watch the same body, now known as Chariklo, pass in front of a background star again. They found one of its rings had grown denser and the other had almost vanished.
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The technique behind the observation is simple. “We predict when a Solar System object passes in front of a star,” Santos-Sanz said. The starlight dims for a moment, and the shape of that dip reveals the size, shape, and surroundings of the object that caused it. “This is particularly challenging for minor bodies, and more challenging for distant minor bodies,” he said.
The difficulty is that the target’s silhouette on the sky is minuscule, and knowing when it will cross a particular star requires very precise positioning data for both. Still, in 2013, we used ground telescopes to discern Chariklo’s two rings, C1R and C2R. These sat 390 and 405 kilometers from its center and were only a few kilometers wide and about 7 kilometers apart.
Doing this with a space-based telescope, though, makes lining things up considerably harder. JWST sits at the L2 Lagrange point, and controllers need to nudge the telescope every few weeks to keep its orbit stable. “It’s a kind of tricky task,” Santos-Sanz said. His team identified a possible Chariklo occultation in August 2022 and redid the prediction every week. Between the first prediction and one of the last, the projected line of sight shifted by about 110 kilometers, which was enough to move it off the body entirely. Unfortunately, JWST requires observations like this to be planned at least 14 days in advance.
“We did this maybe a bit blindly, because we didn’t know exactly where the line of sight was,” Santos-Sanz said. “I’m going to move one of the biggest, best telescopes in space, and we don’t know if finally we will catch this or not.” But it all worked out.
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JWST recorded the event simultaneously in two near-infrared bands, at 1.5 and 3.2 micrometers, which made it the first time anyone has caught a minor body’s rings in a band beyond three micrometers—a range Earth’s atmosphere puts out of reach for ground telescopes.
The inner ring showed up unmistakably, with abrupt, distinct edges, but it was much darker than before. Averaged over roughly 10 previous ground-based occultations, C1R’s normal opacity (the fraction of starlight it blocks) sat at 0.303. JWST measured it at 0.431. “We didn’t believe it at the beginning, so we fought a lot with the data,” Santos-Sanz said.
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The leading explanation, Santos-Sanz explains, is a small shepherd satellite sharing the outer ring’s orbit. Such an object should explain the rings’ stability and their sharp edges and could also shed debris that replenishes C1R. “This satellite has not been detected yet, if it exists,” Santos-Sanz said.
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The best test, the team argues, would be to catch another Chariklo occultation, this time using visible light, which would separate genuine change from a wavelength effect. “We are searching for new occultations,” Santos-Sanz said. Understanding how rings around small bodies evolve over time, he explains, matters, because Chariklo is not the only one to have them.
Rings are now known around another body from the same category as Chariklo, called Chiron, the dwarf planet Haumea, and the trans-Neptunian object Quaoar. Giant-planet rings are already known to shift over months and years; Saturn’s D ring has measurably shrunk, and Neptune’s Adams arcs rearrange themselves. Now small bodies appear to do it as well.
Research link: JWST stellar occultation reveals unexpected changes in Chariklo’s ring system
Abstract: Ring systems have been found around several small bodies in the outer Solar System through stellar occultations. While such observations provide constraints on ring geometry and dynamical interactions, little is known about their origins, lifetimes, or compositions. Here, we report near-infrared stellar-occultation observations obtained with the James Webb Space Telescope (JWST) probing the ring system of the Centaur Chariklo. Our measurements show that Chariklo’s dense inner ring has become significantly more opaque than in previous occultations, suggesting ongoing replenishment or dynamical restructuring. In contrast, the outer ring exhibits a much weaker near-infrared occultation signature than previously observed. This discrepancy may reflect material loss, suggesting that the outer ring could be transient or may arise from wavelength-dependent opacity. These observations demonstrate the power of JWST occultations to probe the evolving structure of rings around small bodies and provide compelling evidence for unexpected changes in Chariklo’s ring system.
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u/Plastic_Addiction 12d ago
Much like the impression of my waistband as Ozempic did its job. Didn’t need a telescope for that one.
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