Pluto: Planet or Not? Come wander with me, she said, Into regions yet untrod; And read what is still unread In the manuscripts of God. - Longfellow

Charon Pluto

The History of Pluto Clyde William Tombaugh discovered Pluto in 1930. Pluto was the name for Hades in Greek myths. He was god of the underworld. His name was given to the planet because it’s so far from the sun that it’s in constant darkness.

Which came first? The planet, or the dog?

Any tie-in to Disney’s Pluto who was created in 1931? The pup first appeared in Walt Disney's short The Chain Gang. Here the dog is named, but it is Rover, not Pluto. It was in "The Moose Hunt", released on May 8, 1931, that the dog is called Pluto the Pup, the studio's original name. Obviously, several months had passed between the naming of what was believed to have been the ninth planet, Pluto, on March 24, 1930, and the attachment of that name to the dog character. Venetia Burney, who as an eleven-year-old schoolgirl had suggested the name Pluto for the planet, remarked in 2006: “The name had nothing to do with the Disney cartoon. Mickey Mouse's dog was named after the planet, not the other way around.” Although it has been claimed that the Disney studio named the dog after the planet (rather than after the mythical god of the underworld), this needs further verification. Disney animator Ben Sharpsteen has said that, "We thought the name [Rover] was too common, so we had to look for something else. We changed it to Pluto the Pup, but I don't honestly remember why. I think we were stoned."

Overview of IAU Congress August 24, 2006 - International Astronomical Union (IAU) met to reclassify Pluto from a planet to a dwarf planet. There are now 8 “true” planets. 3 “dwarf” planets were named.

What is a “true” planet? A “planet” is a celestial body that… is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, has cleared the neighborhood around its orbit. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

What is a “dwarf” planet? A “dwarf planet” is a celestial body that… is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, has not cleared the neighborhood around its orbit, is not a satellite Currently 3 named - Pluto, Ceres, and Eris

Pluto, Eris, Ceres

True Planets vs. Dwarf Planets Orbit around the Sun Sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape Has cleared the neighborhood around its orbit Orbit around the Sun Sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape Has not cleared the neighborhood around its orbit Not a satellite

Small Solar-System Bodies All other objects except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.

Moons of Pluto 2 new moons were named by the IAU Hydra and Nyx Charon still is considered a moon

The Pluto Quadruple System Hydra Nix Charon Pluto Combination of Four Hubble ACS Images Taken on 2006 Feb 15.6 UT

New Horizons Pluto/KBO Mission

Mission to Pluto “New Horizons” is a current mission designed to fly by Pluto and its moons to send data back to Earth Launched January 19, 2006 Should encounter Pluto on July 14, 2015 (will study Pluto for ~9 months) Mission will proceed to the Kuiper Belt (will last 5-10 years)

Launch 2006 January 19 14:00 EST Launched on Atlas V Rocket Fastest Earth departure ever (36,000 mph) Passed Moon’s orbit in 9 hours Pass orbits of: Mars on 4/7/2006 Jupiter on 2/28/2007 Saturn on 6/8/2008 Uranus on 3/18/2011 Neptune on 8/24/2014 Pluto system encounter on 7/14/2015 Total Cost ~$710M (FY08)

New Horizons Year–by-Year

New Horizons “Firsts” First mission to Pluto First since launch Voyager in 1977 to an unexplored planet First mission to explore a double planet First mission to explore an ice dwarf First mission to study Kuiper Belt Objects Fastest space mission ever launched First planetary mission to carry a student built instrument