Tiny body, surprising rings

In 2013, astronomers discovered that Chariklo, a small dark body orbiting between Saturn and Uranus, has two narrow rings. This shocked the scientific community, which thought only giant planets could have rings.

“It was a surprise”

Chariklo is barely 250 kilometers wide

The body is so small that its two rings, called C1R and C2R, sit only 390 and 405 kilometers from its center and are just a few kilometers wide with about 7 kilometers between them.

Watching a star get blocked

Astronomers predict when Chariklo passes in front of a distant star, then measure how the starlight dims to reveal the object's size, shape, and rings. This technique is extremely difficult for distant, tiny bodies.

James Webb makes the shot

On October 18, 2022, the James Webb Space Telescope caught Chariklo passing in front of a background star. The telescope's sightline skimmed just 7.4 kilometers above Chariklo's surface, catching its rings perfectly.

The inner ring got much denser

The inner ring C1R appeared much darker than in previous observations from the ground. Its opacity jumped from 0.303 to 0.431, a change so dramatic that astronomers initially doubted their data.

“We didn't believe it at the beginning, so we fought a lot with the data”

Statistical proof of real change

The team ran 10 million simulations to test if random clumps could explain the density increase. The odds were roughly 1 in 1,000 at one wavelength and 4 in 100,000 at another. The telescope caught the ring twice, making the odds even smaller.

The outer ring nearly vanished

The outer ring C2R barely showed up at one infrared wavelength and disappeared entirely at another, even though the telescope was observing the same stretch of ring in both bands simultaneously.

Material came from somewhere else

The inner ring gained about 10 times more material than the outer ring lost, meaning the extra material did not simply migrate inward. The source of this new material remains a mystery.

“We don't know where the extra material is coming from, but there are some hypotheses”

A hidden moon might explain it

The leading theory is that a small shepherd satellite orbits within the outer ring. This undiscovered moon could stabilize the rings and shed debris that replenishes the inner ring.

“This satellite has not been detected yet, if it exists”

Rings around small bodies evolve

Chariklo is not alone. Rings have now been found around Chiron, the dwarf planet Haumea, and the trans-Neptunian object Quaoar. All appear to change over time, just like Saturn's and Neptune's rings.

More observations needed

The team plans to catch another Chariklo occultation using visible light to confirm whether the changes are real or just a wavelength effect. This will help unlock how ring systems work across the solar system.

“I think this work is just a piece of the puzzle”