The fact that the (former) planet, Pluto, was downgraded to a dwarf planet by the International Astronomical Union in 2006 greatly disturbs some of those I know. In fact, someone close to me feels a particular affinity for the former planet because he grew up in New Mexico and visited the Lowell Observatory as a youngster; Lowell Observatory is the place where Clyde Tombaugh discovered Pluto. (Tombaugh also spent several years teaching in New Mexico.)
So why was Pluto demoted? The discovery of Eris is the major reason for the downgrade to dwarf planet; Eris—another dwarf planet—was discovered in 2005 and knocked Pluto off of ninth-planet-in-the-solar-system status because Eris is 27% more massive, thus proving that Pluto is not a unique object in the Kuiper Belt (similar to the asteroid belt between Mars and Jupiter, consisting of smaller-than-planets objects, except that it’s way bigger and located beyond Neptune).
Pluto is named after the Roman god of the underworld, which goes along with the naming standard of the other planets in our solar system—the Romans observed five bright objects in the night sky that they knew weren’t stars and named them after their gods. You know them as Mercury, Venus, Mars, Jupiter, and Saturn. (When Uranus and Neptune were later discovered, they were also named after mythological gods.) So naming Pluto after a Roman god continues that tradition. Venetia Burney—the eleven-year-old girl that came up with the name—must have had the same thoughts, possibly suggesting Pluto because the god of the underworld had the power of invisibility just as the former planet remained undiscovered for so long. The other two names suggested for the newly-found object were Minerva and Cronus, but Pluto won in a landslide, garnering every vote cast.
Even Pluto’s moons have names tied to mythology associated with the underworld. Charon, the largest of its satellites, comes from the name of the ferryman that transports the dead across the river Styx in Greek mythology. (Since the Roman god Pluto is similar to the Greek god of the dead—Hades—the Greek name Charon has been deemed acceptable as a title.) Styx—the name of that river you had to cross to get to the world of the dead—is the name of another of Pluto’s moons. Pluto’s other moons include: Nix (named after the Greek goddess of darkness and night, who was Charon’s mother), Hydra (named in reference to Pluto having once been considered the ninth planet since the mythological serpent Hydra has nine heads; the H in Hydra was also meant to reference the Hubble Space Telescope, which discovered Hydra), and Kerberos (the Greek spelling of the name of the dog that guards the underworld—since the Roman spelling of Pluto’s Cerberus was already taken by an asteroid).
Finally, you’re probably all wondering how a Disney dog character inherited the name of both a god of the underworld and an at-the-time planet? Well, you can keep wondering because even though many believe Walt Disney officially named Pluto the Pup after Pluto the (dwarf) planet, there is not enough evidence one way or the other to support that theory. Even Ben Sharpsteen, one of Disney’s animators, doesn’t remember why the name Pluto the Pup was chosen.
What is fact is that Pluto the Pup first appeared in the September 1930 Disney film, The Chain Gang, as a nameless bloodhound. His second appearance was as Minnie Mouse’s dog, Rover, and for his third appearance, the pup was dubbed “Pluto” in 1931’s The Mouse Hunt. So the timing does coincide with the discovery of the “new planet”…
Whatever your take on the trio of Plutos—one a dog, one a god, and one a now-dwarf planet—I find all three Plutos quite interesting. I know someone who would choose Pluto the planet as his favorite Pluto, but I am torn in selecting a favorite of my own. Do you have a favorite Pluto? If so, which one?