Two Planets Collide... You Won't Believe What Happens! / Universe Sandbox By Kyan

Universe Sandbox is a physics-based space simulator that allows you to create, destroy, and interact on an unimaginable scale. It merges real-time gravity, climate, collision, and material interactions to reveal our universe's beauty and the planet's fragility.
A collision occurs between two objects when Universe Sandbox detects that the objects overlap in space during a time step. Most object types in Universe Sandbox cannot occupy the same point in space at the same time, and as a result, they may break apart or merge together.