[Nick Zwar]

I agree. Needs to be a hook. Of course, there are some very well known movie themes, often songs, that have become famous on their own, often because they became popular songs. That includes songs like Giorgio Moroder’s “Take My Breath Away” or, to go back further, something like “Unchained Melody” by Alex North, which has become an iconic melody even though hardly anyone has ever seen the movie it was written for.
Henry Mancini’s “Baby Elephant Walk” is another such iconic film theme that has become famous “on its own”. Likewise “Moon River”, which has become such a famous song (whose original sung version by Audrey Hepburn, for whom the song was specifically written, ironically wasn’t released until Intrada’s BREAKFAST AT TIFFANY’S release).

And Goldsmith’s music for PLANET OF THE APES, while not a “hummable” famous movie theme, has been parodied a number of times, including in at least two Simpsons episodes, so it did have some cultural impact.

But for obvious reasons, movie themes that feature easily recognizable, catchy melodies, like the Indiana Jones March or The Magnificnent Seven, are much more likely to become pop-cultural “hits” outside of their movies.