New observations from the James Webb Space Telescope (JWST) show that the two narrow rings encircling Chariklo, a small centaur object located between Saturn and Uranus, have undergone opposite changes in opacity over the past decade. While the inner ring appears significantly more opaque, the outer ring has become noticeably more transparent, a contrast that challenges existing ideas about the stability of rings around minor bodies.
Chariklo and its unusual rings
Chariklo, measuring roughly 250 kilometres (about 400 miles) across, belongs to a population of distant solar‑system objects known as centaurs, which exhibit traits of both asteroids and comets. In 2013, astronomers discovered that Chariklo was the first small body known to possess a ring system, a finding later confirmed by ground‑based observations in 2014 and 2017. Those earlier studies relied on stellar occultations—moments when Chariklo passes in front of a distant star—to infer the presence and structure of the faint rings.
JWST occultation provides a sharper view
In 2022, JWST was positioned roughly 1.5 million kilometres (about 930,000 miles) from Earth, opposite the Sun, and tracked Chariklo’s slow relative motion of 2.5 kilometres per second (1.5 miles per second). Using precise stellar positions from the European Space Agency’s Gaia mission, scientists timed a stellar occultation so that JWST could capture the event with unprecedented resolution. This marked the first JWST campaign deliberately scheduled around a stellar occultation, a technique also employed to study exoplanet atmospheres with the telescope’s infrared instruments.
Comparing JWST’s data with the earlier ground‑based records, lead author Pablo Santos‑Sanz of the Institute of Astrophysics of Andalusia reported that the inner ring’s opacity has increased markedly, whereas the outer ring’s opacity has declined. The study, published on September 9 in Science Advances, outlines three possible explanations for the observed variability.
Possible causes of the ring changes
The first hypothesis suggests that JWST’s finer resolution simply revealed denser and sparser regions within the rings that previous observations missed. A second possibility is that the material composition or the size distribution of the ring grains has altered over time, affecting how much light they block. The third scenario proposes that JWST detected wavelength‑dependent scattering effects, meaning that differences in grain composition or size produce distinct optical signatures at the telescope’s infrared wavelengths.
“Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability,” Santos‑Sanz said, emphasizing that even minor bodies far from major planetary gravities can experience rapid dynamical changes.
Looking ahead
The authors recommend a follow‑up occultation observation the next time Chariklo passes in front of a star to verify the apparent increase in inner‑ring opacity and the decrease in the outer ring. Such data would help separate genuine temporal evolution from effects caused by wavelength‑dependent scattering, clarifying the physical processes shaping Chariklo’s rings.
These findings broaden the understanding of ring dynamics beyond the giant planets, suggesting that small, distant objects may host more active and mutable ring systems than previously assumed.
Norman Pearlstine is the Executive Editor and Co-Founder at News Raise. With over two decades of experience across financial journalism, corporate governance, and market analysis, Norman leads the editorial direction and ensures strict adherence to journalistic accuracy and ethics.
