Why are Chariklo’s two rings changing in opposite ways?
During an October 2022 stellar occultation, JWST measured starlight passing behind Chariklo, a roughly 250-kilometer-wide Centaur orbiting between Saturn and Uranus.[1][2][3] Comparison with a decade of earlier occultations indicated that the inner ring had become more opaque while the outer ring had become less opaque.[1][2][3] Because Chariklo is too small and distant for direct imaging, astronomers infer its rings’ properties from the brief changes in background starlight.[2][3]
The opposing changes challenge the assumption that rings around small bodies are relatively stable and could help researchers identify the processes that form, redistribute and preserve ring material across the solar system.[1][2][3] The observation also demonstrates that JWST can execute precisely timed occultation studies using orbital and positional data from Gaia.[1][2][3]
Key insights
- The physical cause remains unresolved; proposed explanations include particle transfer between the rings, gravitational sculpting by an unseen shepherd moon and wavelength-dependent light scattering.[2]
- The observation required precise knowledge of Chariklo’s orbit, the background star’s position and JWST’s trajectory around the L2 region.[1][3]
- Chariklo moved at about 2.5 kilometers per second relative to JWST during the occultation, slow enough for the telescope to resolve the rings in exceptional detail.[2][3]
- Multi-wavelength follow-up could help distinguish an actual redistribution of ring mass from changes caused by grain-size-dependent optical properties.[2]