ON THIS DAY

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March 13, 1930:

Clyde Tombaugh announces discovery of Pluto at Lowell Observatory.

(The planet, not Mickey Mouse’s pet dog, but have you ever wondered how a clothes-wearing mouse who has a clothes-wearing friend who is a dog (Goofy), and both of whom speak, also has a pet dog without clothes who can only bark?)

Pluto is a dwarf planet made primarily of ice and rock and is much smaller than the inner planets. Pluto has roughly one-sixth the mass of the Moon, and one-third its volume.

On February 18, 1930, after nearly a year of searching, Tombaugh discovered a possible moving object on photographic plates taken on January 23 and 29. The discovery was telegraphed to the Harvard College Observatory on March 13, 1930.

Clyde Tombaugh in Kansas

In 2006, the International Astronomical Union formally redefined the term planet to exclude dwarf planets such as Pluto. Many planetary astronomers, however, continue to consider Pluto and other dwarf planets to be planets.

By the Way:

The name Pluto came from the Roman god of the underworld.

Disney’s Pluto first appeared in the 1930 film The Chain Gang, as a nameless bloodhound tracking escaped prisoner Mickey. He next appeared in the 1930 film The Picnic, however he was portrayed as Minnie's dog, and was named "Rover". In his third appearance, The Moose Hunt (1931), he appeared as Mickey's pet, and was finally given the name "Pluto". Disney animator Ben Sharpsteen claimed they changed the name to Pluto because: "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." Some Disney animators reportedly believed that Disney chose the name "Pluto" to capitalise on the then-newly-named ninth planet of Pluto. However, animation historian John Canemaker states that Disney chose the name simply because he once had a dog named Pluto.

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