When Gustav Holst wrote The Planets between 1914 and 1916, there were but eight known planets in the solar system. Taking out The Earth, that left seven movements in his suite. When Pluto was discovered in 1930, he refused to add a new movement (although some musical necrophiliac did in 2000). Imagine what he'd do with yesterday's news that scientists and historians (?) have proposed a new definition of "planet" that would not only settle the status of lowly Pluto, but would actually add three new planets to our solar system: Ceres (currently a large asteroid), Charon (previously a moon of Pluto), and 2003 UB213 (aka "Xena").
The new definition of a planet includes "that an object be massive enough that gravity has formed it into a sphere and that it circles a star and not some other planet." Not everybody is happy about this:
The difference, according to the definition, is that the center of gravity for Pluto and Charon is between them, not inside either one. So technically, Charon is not orbiting Pluto but is orbiting the center of gravity of the two bodies. The center of gravity for the Earth and its moon, on the other hand, is inside the Earth. Dr. Boss calls this 'a legalistic definition.'Gods save us from legalistic definitions!
One wonders what Holst would have made of all this. A four-movement sequel. The Planets, II, I think. Subtitled "Pluto's Revenge," or somesuch. I'm sure Hollywood would make a movie out of it.