As someone with a passing interest in modular/generative sound, this was really neat to play with! Lots of potential here. I'd love to play an expanded version with more sound options. Maybe a planet that plays a really long sound? Or one with percussive noises? A way to quantization to the 12-tone scale would also be cool.
Unfortunately, I also wasn't able to add additional planets. For a tool like this, I'd suggest adding some UI buttons in case the keyboard controls don't work (i.e., bugs, touch-only devices).