I know how difficult it is to create the gravity system on each planet, since I've worked on something similar.
And despite getting stuck on one planet with no way to escape (when I tried to move on to the next one, I crashed and returned to the planet I started from), the game is original and I liked it!
The music is also very nice.
You could add a full screen mode so I can appreciate it better, since I played it on a small screen in the browser and there's no option to enlarge it :)