I say either Jupiter or Neptune from Holst's collection of pieces entitled, The Planets. Actually, anything classical is not that hard to relate to the book because of the wide range of emotions shown. Such as when Kit figures out what the "dark space" is, there could be a song that sounds spirited or exciting. And when Nita is depressed about her mother's illness, you could have a slow type of classical song with violins that gives you the impression of saddness or lonliness.
************************
************************
Comment