A simple mod for muting an individual planet's music. It also has support for muting the space platform music, and the main menu.
Note that this won't be very helpful for multiplayer unless everyone want the same planets muted, because it is applied globally. I did look for a way to do it per player but I couldn't find anything even close in the documentation.
The way this works is by overriding any music tracked listed specifically for each planet with a silent sound file. This avoids causing nil references and should generally avoid breaking other things, but could still cause some weird issues if a mod has structured their sounds differently.
Because they're defined differently, this shouldn't affect any of the ambient sounds on each planet, only the main music tracks.
Sadly modded planets do all have to be added individually, since I don't think there's any way to programmatically add settings.
If there's any issues or there's a planet you want added please open a thread in the discussion tab.