Gustav Holst didn't even know Pluto was a planet - or a dwarf planet - when he started to compose his seven-movement suite The Planets in 1914. Pluto wasn't discovered until 1930 and by that time, Holst had no interest in adding another movement to his well known work.
Each of The Planets' seven movements is titled after one of the other-earthly planets known at the time. He composed them all in order from "Mars" to "Neptune," except "Mercury," which he wrote last, although it was ultimately placed third in the suite.
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