Pluto, one of the largest of the dwarf planets in our solar system, is known to have at least five moons. Three of these have already been assigned common names, while the two that were discovered most recently were known simply as P4 and P5. They have now been given the names Kerberos and Styx. A drive led by Star Trek actor William Shatner to have one of the moons named Vulcan was rejected by the official naming body.
The planets were discovered by the Hubble Space Telescope in 2011 and 2012. In February 2013, an internet poll was held to vote for new names, given a choice of Vulcan, Cerberus, and Styx, among others. The poll attracted half a million votes from people around the world. Vulcan and Cerberus won the vote, partially due to a grassroots effort in support of the name Vulcan, both a god of fire and volcanoes, as well as a reference to Mr. Spock's home planet on Star Trek.
The International Astronomical Union (IAU), which is the only body allowed to officially name celestial objects, rejected Vulcan because the name vulcanoid refers to asteroids within the orbit of Mercury. They then modified the spelling of Cerberus to Kerberos, the Greek spelling, to avoid confusion with the asteroid 1865 Cerberus.
The innermost moon to the planet, and the first one discovered in 1978, is Charon. As you head further away from Pluto, the next moon out is Styx, then Nix, Kerberos, and Hydra is in the most distant orbit.
"Kerberos has an estimated diameter of [eight to 21 miles] and Styx is thought to be irregular in shape and is [7 to 17 miles] across," the IAU reported.
The three previously-named moons around Pluto were all named after mythological creatures, a tradition continued with the two smallest moons. Styx was a Goddess who ruled over a river with the same name, which the dead must cross on their way to the underworld in ancient Greek myth. Kerberos, or Cerberus, was a three-headed dog in Roman mythology which prevented souls who had entered the underworld from ever leaving.
Once known as the ninth planet, Pluto was demoted by the IAU to dwarf planet status in 2006. Four other bodies like Pluto have been found, one of which, Eris, is 25 percent more massive than the former planet.
"The discoveries of Kerberos and Styx add to the mysteries surrounding the formation of the Pluto system," Alan Stern, principal investigator for the New Horizons spacecraft, said. That craft, due at its destination in 2015, will be the first one to ever fly by Pluto.
