OG SC-49 教えて下さい

The cameras of the Voyager 2 spacecraft detected six small, previously unseen moons circling Uranus, <which doubles to twelve the number of ssatellites now known as orbiting> the distant planet.

A)
B)doubling to twelve the number of satellites now known to orbit
C)which doubles to twelve the number of satellites now known in orbit around
D)doubling to twelve the number of satellites now known as orbiting
E)which doubles to twelve the number of satellites now known that orbit

特に「doubling to twelve the number of satellites」の訳がわかりません。 教えて頂ければ幸いです。