Acheron and Empyrean each have a giant space station which wraps around the planet. Each station is a Cepheus Ring. The Cepheus Rings are joined together by the Erebus Bridge.
The album art for Xenon shows Acheron, Empyrean, a Cepheus Ring around each planet, and the Erebus bridge joining them.
Acheron and Empyrean encircled by Cepheus Rings
Cepheus Ring concept art
