One of my favorite games so far in this game jam. Love the story and the game mechanic, but in some levels I was not sure what to do and just hoped that i hit my next destination somehow. You get a plus because you made your music yourself instead of taking any finished track from somebody else. I did the same for my game and I have the same repetitive music, but mine is shorter :D Maybe you want to check it out. I would appreciate it.
Here are some points which could be improved for your game if you plan continue to work on it. I could see a nice mobile game here ;)
- Some levels can be completed with not using all planets, but I think it's quite hard to balance this in a physics driven game. One level can also be completed without using any planets :D
- Somehow the controls for placing and scaling the planets doesn't feel very intuitive for me. You could try to go with 1, 2, 3, ... for choosing the planets (3 and up if you plan to implement more). And for the scaling I would like to see the mousewheel.
Other than that I can't find anything bad :D Btw. I like that you used your game mechanics for the start screne ;)
One question at the end: Did you use point effectors for the gravity or is this all code? Or something else? :D