I liked this very much. I will look into the code later. The only "issue" I found is that planetary motion (gravity) make object orbit in ellipses with Sun at one of the focii of the orbit. (In reality is the center of mass of the whole system, which for the solar system is right inside the Sun, but never mind those details).
Other than that, I found it very interesting and relaxing to watch it run. Congratulations!!!