Interesting Idea.
Some Feedback:
It would be cool if the win condition could depend on the stability of the orbits. You could just destoy planets on collision, and see if 3 seconds in the simulation all conditions are still fullfilled.
Also the lack of sound was a bit strange.
BTW. there seems to be a bug, where sometimes there is just no background image.
With a bit of polish, I think it could be a fun game!
And kudos on making all of the assets yourself!