Even though 'Vulcan' was the top choice among voters, the International Astronomical Union opted to go with the second- and third-most-popular proposed names. Pluto's fourth and fifth moons are now officially known as Kerberos and Styx.
The people have spoken. And then they were ignored.
After the discovery of Pluto's fourth and fifth moons, in 2011 and 2012, the International Astronomical Union asked the public to vote on what to name the erstwhile planet's satellites, which at the time were known as P4 and P5. The winning candidate: Vulcan, sparked by a tweet from none other than William Shatner, who proposed the name. It received more than 170,00 votes.
But the IAU opted to go with the second and third choices, each of which received less than 100,000 votes, and the official names of P4 and P5 are now Kerberos and Styx, respectively.
Even though "Vulcan" hewed to the IAU's rule that the name had to come from classical mythology – in addition to being the name of Mr. Spock's homeworld, Vulcan is also the name of the ancient Roman god of fire and metalworking – the IAU had its own reasons to reject it. From their press release:
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).