Pluto's Fourth and Fifth Moons Named Kerberos and Styx
Posted on July 4, 2013
Pluto's fourth and fifth moons have officially been named Kerberos and Styx. The moons, discovered in 2011 and 2012, were previously known as P4 and P5.
The names Cereberus and Vulcan were selected in a public poll conducted by the Seti Institute. However, the International Astronomical Union (IAU) - the arbiter of the naming process of celestial bodies - has the final say. The names were required to be mythological names about the underworld.
Cerberus was changed to Kerberos - the Greek spelling of the word - to avoid confusion with an asteroid called 1865 Cerberus. The IAU also explained why Vulcan was not chosen in its press release.
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.NASA has information about Pluto here.