解释个句末分词的作用

In the past several years, astronomers have detected more than 80 massive planets, most of them as large or larger than Jupiter, which circle other stars.

答案是C：most of them at least as large as Jupiter, circling

请问circling是什么作用啊？作伴随状语还是结果状语?好像都不对。请教，谢谢