“We don’t know where the extra material is coming from, but there are some hypotheses,” Santos-Sanz said.
The ghost moon
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.
A computer model based on JWST data also hints at what the two rings are made of. Santos-Sanz, though, makes it clear that this part of the work is unfinished. “Our feeling after this model is that the inner ring should be composed of bigger particles than the outer ring. The outer ring we think is more dusty,” he said. “But this is a work in progress. I can’t say with certainty, well, this is dusty, this is not.”
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.
“I think this work is just a piece of the puzzle,” Santos-Sanz said, “but it could be an important clue for broader studies about the rings around minor bodies and around giant planets.”
Santos-Sanz’s study is published in Science Advances: https://doi.org/10.1126/sciadv.aeh4794