Ownership is the category of real right.
So I think the "object of ownership" you mentioned in this question should refer to the object of real right.
The object of real right is "thing", which refers to any property that exists outside people, can be dominated and controlled by manpower and can meet people's needs.
The sun, the moon and the stars are beyond our control, so they are not "things" and therefore are not the objects of ownership.
About artificial limbs. Prosthetics, as a commodity or article, is a kind of property that exists outside our human body. It can be used and dominated by us and can meet some of our needs, especially for patients who need prosthetics, so it is a kind of "thing", that is, the object of ownership.
But what we're talking about here is "prosthetic limbs on patients." First of all, as an organ on the patient's body, it becomes a part of the patient's body. At this time, he has changed from the object of property right to the object of personal right, which does not conform to the definition of "thing", so he is not an object of ownership. When the prosthesis is removed from the human body one day, it becomes a thing again.
Whether it is a "thing" (the object of ownership) depends on whether it is outside or inside people. The key is whether you can leave the human body. If it is a part of this person's body, it cannot be separated from the person, and he belongs to the object of personal rights.
For example, a pacemaker was originally a thing and an object of ownership, but when it was put into a person's body, you thought that a person's heartbeat depended on him and was inseparable, and he was no longer a thing. The same is true of artificial limbs. Simply put, when people rely on it as much as every organ of our body, it is no longer a thing.
Another example is hair, which is the object of our personal rights when it is on us, but it can be sold when it is cut off and become a thing, that is, the object of ownership.