So Pluto can't sit in the dining room with all the grown-up planets - it has to sit at the rickety card-table with the kids. And I can't find any songs about Pluto. Are there any? On this page of mp3s, not even any of these wonderful late-'50s "Space Songs" for kids mentions the former ninth planet. Hell, even Uranus gets its own, albeit crappy, song: "Journey To The Seventh Planet," the theme song to a delightfuly bad '50s sci-fi flick*.
At least Frank Sinatra mentions Pluto (in the most disparaging of terms) in this excerpt from his most bizarre recording, "Reflections on the Future," from his 1977 3-record set "Trilogy." All of the third disk was a conceptual song-cycle by Gordon Jenkins, who practically invented the concept album - my 1949 copy of his New York-themed "Manhattan Tower" is the oldest LP in my collection.
Frank Sinatra - "Reflections on the Future (excerpt)" - a groovy trip thru the solar system; and when he sings "Uranus is heaven" he doesn't pronounce it the way you would have.
*Big thanks to the awesome Essential Ghouls Record Shelf