Lyric discussion by Superabound 

In this song, Earth is unique in the cosmos, for it is the only planet where music exists. An alien happens to hear it one day and is intrigued, so he goes searching for it. He follows some signals to Mars and meets and astronaut who is exploring it, and who informs him that the actual Planet of Sound is "one more over"--Earth.

Not quite the only one. When he mentions Mars (the red renowned place) he says that Martians can hear our music too.

@Superabound I believe the astronaut is on the Moon. Hence the river: one of those vehicles they used on the Apollo missions.

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