Is Space Not the Same Everywhere?

If your system is just the rock then momentum is no longer conserved. And so in that scenario the momentum of the rock is not conserved because space is not the same everywhere The answer you get depends on where you are in space But in that case now you're sort of expanding your system and momentum is conserved between them. Isn't it exactly if you include the planet in the system then momentum is Conserved anywhere? It's something to do with this idea of symmetry and the equations of physics, right?