This is a really nice polished, cohesive experience! The flow of the environment from the pond to the spaceship with a few objects of interest along the way works very well and that journey is reflected well in the music. The sparseness of the music is very fitting and I would try to preserve that if you add this. I really don't have many ideas for what you could add to this - I think it works quite well as is. Adding a filter effect while underwater is an obvious idea and it might be nice to have sound sources that move through the environment, but that depends on how lively you want the space to feel. Also since looking at the sky feels meaningful with all the stars and constellations, maybe you could change the music based on where the player is looking.