A while ago I made a physics simulator for projectile motion which would gravitate towards the ground. I decided to build off this idea and make a free space gravity simulator!!!
To launch new planets, click and drag. When the planets collide, they will create a larger planet with a greater mass. The dynamics of this were done in a 3D perspective, so that is why planets grow very slowly in proportion to their mass build up (the mass is proportional to the cube root of the radius). Check it out!
Conservation of momentum is followed, so launching a small planet with a high velocity at a large planet will produce a small velocity change due to the mass difference :)