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Kerberos and Styx named as moons of Pluto

Posted July 2, 2013

Pluto's moons

The International Astronomical Union (IAU) announced Tuesday that names voted on by the public had been accepted for Pluto's fourth and fifth moons.

Kerberos and Styx, formerly known as P4 and P5, join Nix, Hydra and Charon. The names maintain the theme of classical Greek mythology involving the underworld.

In Greek myths, Kerberos (or Cerberus in Roman myths) is a three-headed dog guarding the gates to the underworld. This "hell hound" prevents those who have crossed the river Styx, which separates the underworld
from Earth, from returning. The ferryman Charon, son of Nix the Greek goddess of night, brings souls across the river to Pluto (or Hades in Roman myths), god of the underworld.

Hydra was a nine-headed serpent which doesn't fit quite so nicely into the underworld myths but Pluto's discovery as a ninth planet has been mentioned as motivation for the name as well.

The newly named moons were discovered in 2011 and 2012 by a research team led by Mark Showalter of the SETI Institute using the Hubble Space Telescope (HST). Nix and Hydra were discovered also using HST in 2005.

The honor of naming planetary bodies is usually given to the discovery and their team. Showalter chose instead to open naming up to the public. After over 450,000 votes, Vulcan, Cerberus and Styx topped the
votes and that list was submitted to the IAU's Working Group for Planetary System Nomenclature and the Committee on Small Body Nomenclature.

Though it did receive the most public votes, Vulcan was rejected because of the name's association with vulcanoids, or asteroids inside the orbit of Mercury. Cerberus was changed to Kerberos to maintain Greek naming and to prevent confusion with 1865 Cerberus, a 15 city-block-long asteroid that crosses the orbit of Mars and Earth.

Images of the new moons along with Pluto and its other natural satellites are little more than points of light in HST images.

Researchers eagerly await the arrival of the New Horizons missions in July 2014. After a more than 8-year journey, New Horizons will fly by Pluto gathering information on the planetoid's atmosphere, surface, and geology as well as measure the effects of the solar wind at the outer reaches of the solar system.

When launched in 2006, mission managers supplied the spacecraft with a pair of quarters from Florida, where the spacecraft was launched from, and from Maryland, where it was constructed. These quarters serve the practical purpose balancing the spinning spacecraft but also provide a ceremonial toll to cross the river Styx past Pluto and onto the Ort Cloud beyond.


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  • Tony Rice Jul 5, 2013

    @knight27243, true planets get Roman names, moons generally get Greek ones. For example, Mars is the Roman god of war, it's moons Phobos and Deimos (twin brothers and sons of Greek god of war, Ares)

  • knight27243 Jul 4, 2013

    Actually the planetary names were used in Roman mythology not Greek. I.e.: Hades is the greek god of the underworld, Pluto is his Roman counterpart