“Don’t mind us. We’re just here for the Nickel-Iron and H2O. All of it.”
Which makes no sense what so ever.
You can find all of that in much purer forms free floating in space. Grab it, haul it to your space based processing factory, (solves the heat and pollution issues) and make what ever you want out of it.
The only movie I have ever seen that had the aliens harvesting a resource that made sense, Jupiter Ascending, was truly awful in every other way.