Hephaestus is the only moon of Vulcan.
Hephaestus is thought to have formed around a particularly violent star that would eventually throw the planet and its moon out of its parent star system. Tracebacks have determined that Vulcan originated from RS 8409-1353-8-11843423-10, a white dwarf 11.843 light years from Sol.
Hephaestus is thought also to have become Vulcan's moon after it wandered into Vulcan's orbit early in the history of its parent star system.
Hephaestus was first detected by the Extrasolar Body Tracking System, or EBTraS. on January 26, 7011. The EBTraS AI initially determined that its parent planets trajectory would cause it to pass through Jupiter's orbit. Upon further extrapolation, EBTraS determined Hephaestus would initially pass harmlessly through Jupiter's orbit before being caught in an orbit that would cause it to strike Jupiter.
However, due to Vulcan's orbit predicted to strike Europa, the planetary government hired Terragen to help alter Vulcan's orbit, which would cause Hephaestus to move with its parent planet. As the moon approached Sol, the increasing heat from the sun melted long frozen gases on Hephaestus, creating atmospheres on both worlds and turning both into hot Ae-Class worlds.
Hephaestus immediately became a popular destination for tourists as well as a popular place for certain eccentric people to retire.
Most of the moon's population are eccentric retirees who live in very heavily shielded domed habitats with robotic help. The low gravity helps keep them limber and living longer. Others who live there are owners of popular recreational centers.
Unlike its parent, Hephaestus has a substantially more Earthlike day despite it being nearly twice as long as Earth's own. This means that the entire surface is more equally bathed in heat and radiation, keeping the surface constantly boiling.
The moon, like its parent has a strong magnetic field that deflects much of the incoming solar radiation.