‘Chiron,’ the strange half-comet, half-asteroid beyond Saturn, is now developing its own ring system, study finds
In a universe where change typically unfolds over eons, astronomers got a rare front-row seat to watch a small, icy world beyond Saturn build a whole new set of rings in real time.
A team of astronomers based in Brazil has discovered that the bands of matter orbiting around (2060) Chirona 200 kilometer wide object that circles the sun between Saturn and Uranus, are new and still taking shape. The results suggest that Chiron’s surroundings are in a transition state somewhere between a chaotic cloud of debris and a fully formed ring system, providing scientists with a rare snapshot of ring formation in progress, something that has never been directly observed before.
Chiron joins the asteroid Chariklo and the dwarf planets Hauméa And Quaoar as one of four small worlds in our solar system known to host rings, but it is perhaps the most dynamic of all.
Chiron’s changing environment, detailed in an article published October 14 in the Letters from astrophysical journalscould help scientists understand how small, icy objects as well as giant planets like Saturn and Uranus built their iconic rings billions of years ago.
Rings in preparation
Made up of rock, water ice, and organic compounds, Chiron belongs to a strange population of objects called centaurs, which orbit between Jupiter and Neptune and behave partly like asteroids and partly like comets. Chiron orbits the sun once every 50 Earth years.
Since its discovery in 1977, astronomers have seen it occasionally brighten and even sprout a slight tailproof that it sometimes releases gases and dust into space.
In September 2023, when Chiron briefly crossed in front of a distant star from Earth’s perspective, the Pico dos Dias Observatory in Brazil detected repeated tiny dips in the star’s light. When the researchers compared this data to similar events cataloged in 2011, 2018 and 2022, they found that the three distinct, dense rings – orbiting at a distance of about 170 to 270 miles (270 to 430 km) from Chiron’s center – had remained in place for more than a decade.
In the 2023 data, the team also spotted a new disk-shaped structure extending from about 120 miles to 500 miles (200-800 km) around Chiron that had not appeared in previous data. The larger, diffuse disk probably only formed in the last decade, perhaps following a collision or explosion that released fresh material into orbit, Pereira said.
Intriguingly, the team also discovered a faint outer feature nearly 1,400 km from Chiron – well beyond what is known as the Roche limit, the limit where the ring’s materials should clump together to form a moon rather than remaining as debris, the new study notes.
“This is the first time we detect a material signature in this region,” Pereira told Live Science, adding that higher-resolution observations are needed to confirm it. “Beyond this limit, the particles forming a ring should naturally start to merge to form a satellite – but something seems to prevent this from happening.”
Researchers aren’t sure what caused Chiron’s strange configuration. One possibility is that volatile ices beneath its surface erupted in a comet-like explosion, ejecting dust and ice that then settled into orbit. Another is that a small moon broke apart, scattering fragments that spread along Chiron’s equator, according to the new study.
The latter theory could also explain Chiron’s steady brightening over the past decade, which is difficult to explain by cometary activity alone, Pereira said.
Other experts say the results raise new questions about how rings around small bodies can survive for long periods of time.
“It may be that something adds energy to these particles and allows them to persist beyond the limit without merging,” Keighley Rockcliffea postdoctoral researcher at NASA’s Goddard Space Flight Center in Maryland who was not involved in the new paper, told Live Science by email.
It could also be that the ring is very diffuse or simply hasn’t existed long enough to coalesce, Rockcliffe said. “Maybe he trained recently and didn’t have the opportunity to train a little centaur.”
To confirm whether Chiron’s rings are actually evolving, and not just looking different from our changing perspective, astronomers hope to capture more events in which Chiron passes in front of distant stars. Such events, when recorded with high-speed cameras at observatories across multiple continents, provide the only direct way to see whether the disk material is changing in terms of opacity, width, or position—signs that Pereira said would reveal that dust and ice are actively redistributed, offering direct evidence of ongoing evolution.
“The ideal scenario to satisfy our curiosity, however, would be a space mission dedicated to in situ observation of this intriguing system,” Pereira said.
