Pretty good. It'd be even better if you have the planets be able to react to the other object's gravitational pull. And it'll be more accurate if you use leapfrog or some integration method to calculate the positions. Take a look at my Physics of Planets simulation. It might give you some ideas.

I'm trying to add a comet launcher where you can flick comets with the mouse but I cant make so that after you let go that it keeps on drifting.could anyone help me!