The International Astronomical Union (IAU), which likes to present itself as the decider of all things astronomical, issued a press release on names for the Moons of Pluto today:  Names for New Pluto Moons Accepted by the IAU After Public Vote –  IAU.

Mark Showalter  of the SETI Institute led the  team that spotted the new Pluto-ian moons with the Hubble Space Telescope. He

decided to call for a public vote to suggest names for the two objects. To be consistent with the names of the other Pluto satellites, the names had to be picked from classical mythology, in particular with reference to the underworld — the realm where the souls of the deceased go in the afterlife. The contest concluded with the proposed names Vulcan, Cerberus and Styx ranking first, second and third respectively. Showalter submitted Vulcan and Cerberus to the IAU where the Working Group for Planetary System Nomenclature (WGPSN) and the Committee on Small Body Nomenclature (WGSBN) discussed the names for approval.

However, the name Vulcan had already been used for a hypothetical planet between Mercury and the Sun. Although this planet was found not to exist, the term “vulcanoid” remains attached to any asteroid existing inside the orbit of Mercury, and the name Vulcan could not be accepted for one of Pluto’s satellites (also, Vulcan does not fit into the underworld mythological scheme). Instead the third most popular name was chosen — Styx, the name of the goddess who ruled over the underworld river, also called the Styx.

Here is a SETI Institute video with a discussion of the name selection: