Chariklo's two rings changed in opposite directions
A stellar occultation planned specifically for the James Webb Space Telescope indicates that Chariklo's inner ring became more opaque while its outer ring became less opaque. Comparison with measurements from the past decade suggests rings around small bodies may be more changeable than assumed. The contrast could reflect physical evolution, differences between observational filters, or both.
Science··Midday
The inner ring darkened as the outer one faded
Chariklo, a small body roughly 250 kilometres across orbiting between Saturn and Uranus, has two narrow rings that changed in opposite directions within a few years. The Instituto de Astrofísica de Andalucía says the inner ring blocked more starlight in a James Webb Space Telescope observation while the outer ring blocked less. Europa Press likewise reports that comparison with the past decade's measurements made the inner ring look more opaque and the outer one less opaque.[1], [2]
The measurement rests on a brief fading star
Because the rings are too narrow to image directly, astronomers measured the brief dips in light as Chariklo crossed in front of a star. The observation on 18 October 2022 was the first predicted stellar occultation planned specifically for Webb and successfully observed. Chariklo's low relative speed of 2.5 kilometres per second across the telescope's view allowed the ring structure to be measured at higher spatial resolution.[1], [2]
The physical cause remains open
Study leader Pablo Santos-Sanz says the two rings changed in opposite directions compared with earlier occultation observations. Europa Press adds, however, that the contrast could arise from physical ring evolution, differences between the filters used for the observations, or both effects together. The institute's narrower conclusion is that rings around small bodies may be less static than previously assumed.[1], [2]
