Webb study finds contrasting changes in Chariklo’s two rings

Astronomers have found that the two narrow rings around Chariklo, a small body orbiting between Saturn and Uranus, appear to have changed in opposite ways within only a few years. The inner ring has become significantly more opaque, while the outer ring appears less opaque.

The finding comes from comparing observations gathered over the past decade with data from the James Webb Space Telescope. On 18 October 2022, researchers used Webb to watch Chariklo pass in front of a distant star. During this stellar occultation, tiny dips in the star’s light revealed details of rings that are too narrow and distant to photograph directly.

The observation was the first stellar occultation specifically predicted and planned for Webb, then successfully carried out. It required precise calculations of Chariklo’s orbit, the background star’s position and the telescope’s location in space.

Chariklo is about 250 kilometres across and lies nearly 17 times farther from the Sun than Earth does. In 2013, it became the first minor body known to have rings. The new study, published in Science Advances, challenges the earlier view that such rings are relatively stable. The reason for the apparent changes remains uncertain and could involve genuine evolution, differences between observational filters, or both.