I actually manged to finish all 10 levels :) (Don't know if I'm the first :D )Once I figured out that you could look at one orbiting planet and shoot when it reached a certain position because all the other planets had consistent positions relative to it (if that makes sense) the game became easy. I liked the music and sounds effects especially.
I found a bug where a an orbit would go green but the planet would sometimes be destroyed or go off orbit slightly, this happened especially on the inner planets. Also I know you were going for a minimalist design but I would've liked to see at least some simple patterns on the planets to make them look a bit more pretty.
The game play was simple and fun. Nice job!