Thanks for your feedback. Actually we are friends on ldjam.com where I tried to help you compile your game for windows/WebGL because I really wanted to play it. I really love it that you like my game.
The physics part was quite interesting to program. The player has a rigidbody that is switched to kinematic when on the planet and switched to dynamic when in space. For the controls on the planet i'm using script only. In space I use forces for the jetpack and point effectors for the planet gravitation.
I really wanted to have some sort of tutorial that guides you through the controls while playing, but that would have been too much work for that week. But I will definitely go for such an approach if I continue to work on the game, which I'm really planning to do after the good feedback I get.