Hephaistos And Hades

Poul Anderson, Harvest Of Stars, 58.

Hephaistos is the innermost planet of Alpha Centauri A, the equivalent of Mercury in the Solar System. Both of these inner planets are used for antimatter production. In the Centaurian System, Lunarians and Demetrians share skills, resources and robots to build production facilities either on or in orbit around Hephaistos. However, the Lunarians, possibly aiming at interstellar travel, come to need considerably more antimatter than can be feasibly stored in the kind of units used at Hephaistos.

Alpha Centauri A and B had captured the faint red dwarf, Proxima Centauri, thus wreaking havoc in the double star's outer cometary cloud and, to a lesser extent, in its inner cloud where a series of collisions possibly produced Hades:

mostly ice;
rock core;
mass nearly 1% Terrestrial;
noticeable gravitation;
no magnetic field;
too far out to be affected by solar winds.

The Lunarians put their excess antimatter, mostly antihydrogen but also some antihelium plus solid spherules of heavier nuclei, in orbit around Hades with four small asteroids functioning as stability-maintaining shepherd satellites on periodically adjusted orbits between the ring of antimatter and an outer ring of ordinary gas. Expensive but profitable.