Rings around a tiny body have changed over the past decade
摘要
2013年，天文学家发现土星与天王星之间的小天体“卡里克罗”拥有两道窄环，打破了行星才有环的认知。近期，桑托斯-桑斯团队利用詹姆斯·韦布空间望远镜再次观测卡里克罗掩星，发现其中一道环变得更密集，另一道几乎消失，原因尚不明确。该观测依靠预测天体遮掩背景恒星、分析星光变暗曲线来揭示天体及其周围环境，对遥远小天体尤其困难。
For decades, astronomers thought rings were something only giant planets had. That changed in 2013, when a small, dark body orbiting between Saturn and Uranus passed in front of a star and blinked twice on either side of the main event, revealing two narrow rings around an object barely 250 kilometers across. “It was a surprise,” says Pablo Santos-Sanz, an astronomer at the Instituto de Astrofísica de Andalucía in Granada, Spain. Ever since, the question has been what such rings are made of and how long they can last.
In a recent study, Santos-Sanz and his colleagues used the James Webb Space Telescope to watch the same body, now known as Chariklo, pass in front of a background star again. They found one of its rings had grown denser and the other had almost vanished. We don’t know exactly why.
Shadowing a star
The technique behind the observation is simple. “We predict when a Solar System object passes in front of a star,” Santos-Sanz said. The starlight dims for a moment, and the shape of that dip reveals the size, shape, and surroundings of the object that caused it. “This is particularly challenging for minor bodies, and more challenging for distant minor bodies,” he said.
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