A tiny world's rings are changing — in opposite directions at once

Chariklo is a speck of a world — an icy body about 250 kilometres (155 miles) across, orbiting the Sun between Saturn and Uranus. In 2013 astronomers were startled to find two thin rings around it; until then, rings were thought to belong only to giant planets. Now the James Webb Space Telescope has watched Chariklo slip in front of a distant star, and the way the starlight dimmed as it passed through the rings told a new story. Comparing that shadow-play with similar star-crossings over the past decade, a team led by Spain's Institute of Astrophysics of Andalusia found the inner ring has grown noticeably more solid while the outer ring has faded — the two are changing in opposite directions, measurably, within just a few years. Astronomers had assumed a small world's rings would sit still. The study, published in Science Advances, shows they are active, evolving places instead — and this was the first star-crossing ever planned specifically for Webb, a neat proof of how precisely the telescope can be aimed.