What does St. Thomas Aquinas mean by 'alteration' of heavenly bodies in Summa Theologiae?

In Summa Theologiae, when talking about "The quality of the world after judgement ", in the 4th article the reply to objection 4 states: > "Reply to Objection 4. This brightness will be in these bodies even as it is in the heavenly bodies, in which it causes no heat, because these bodies will then be un*alterable*, as the heavenly bodies are now." Here, what does St. Thomas Aquinas mean by *alteration*? In the reply to objection 4, he says *these bodies* will be unalterble. From *these bodies* I understand that he means things on earth, ie; bodies other than heavenly bodies. If things on earth become unalterable after the judgement, how can redeemed man make use of them as St.Thomas Aquinas states in reply to objection 5 of the 3rd article, in the same link I provided above, that: > "...thus man will make use of other creatures..." I think reading the full 4th article in "The quality of the world after judgement " will help a lot in answering the question. I hope my question is understandable:)