AI isn’t self-sustaining. Remove the human technician’s for a little while and any AI system will collapse naturally; this is about controlling people, not machines.
The number of known planets is already in the thousands and soon enough will be in the millions. For now, most of the known bodies are large, but as time goes on smaller and smaller bodies will be detected. There’s no possible definition of ‘planet’ that will be able to place all of these objects into neat categories. Create a rule if you want, but realize there will always be exceptions, like Pluto, our ninth planet. Because we say so.