Merging Object

I am trying to simple merge 2 spheres together so that they act as 1 rigid body instead of 2. Like they are welded and so that 1 appears indented into the other. All of this happening during runtime. What I am doing is trying to make a POC for solar system simulation in Unity3d. I have the gravity worked out, just not how to merge objects like I said above. I haven’t really ever tried anything like this and have no idea where to start. Any help or pointers in the right direction will be appreciated thanks!

You can go about this a couple of ways:

1: Create an empty gameobject, create 2 spheres, move the spheres into the positions that you’d like, and then drag and attach them to the emprty gameobject, and then attach a Rigidbody component to the gameobject.

2: Create 2 spheres, move them into position, drag and attach 1 of the spheres onto the other. Which should have the same effect as the 1st solution.