Convert 2D material to a 3D "object"?

For example…
This is just a made up example…but it is similar.
Say I have a shader that displays the solar system and planets rotating around the sun.
I can create a custom HLSL node and make a material that displays it.
But it is being displayed on a 2D surface.
How do I make it so it exists in the 3D world of the scene itself?
So that I can have my character walk around it?