The ultimate aim of terraforming is to create an uncontained planetary biosphere like Earth i.e. one that would be hospitable for human beings.
Terraforming has come to a halt and no one can leave the tower.
Terraforming is a hypothetical science of developing a living, breathing earth-like conditions from the uninhabitable.
Terraforming and colonization come with inherent risks such as intergalactic war, alien encounters and natural disasters.