- "The Sphere is a civilization unto itself. A living thing. "
- – Mother, explaining to Tommy what Sphere is. [src]
The Sphere is a massive alien vessel whose inhabitants invaded Earth to harvest the planets inhabitants, further populating the sphere.
The origin of the Sphere is unclear but it is believed that the Sphere was created by The Keepers. Its main goal is to maintain itself. It travels the galaxy searching for various alien races to maintain it. It also uses these races as food to provide much needed extra energy to sustain the Sphere and its inhabitants. While Keepers seems to be the creators of Sphere, they have little control over it and act more like passengers, than actual authority on the Sphere.
The Sphere is controlled and maintained by the many diverse and alien creatures living inside, some of which appear to be sentient and others seem to be no more than animals. Many of the Sphere's inhabitants are aggresive and warlike, though it also contains populations of a variety of passive alien species. There is even a group of humans living here in secret, fighting against the hostile forces of the Sphere.
The Sphere is controlled by a creature, be it human or alien, in the center of the Sphere. The controller of the Sphere has absolute power of it and can do anything. When a kidnapped creature manages to get to the center of the Sphere, the controller at that time, makes a deal with the creature to take his place as a controller of vessel. Even if the creature refuses the deal, after the former controller dies, the creature will automatically become the new controller of the Sphere. It seems no matter if the new controller has good intentions, the power he gains, corrupts him and makes him only care about extending Sphere existence. This nearly happens to Tommy but he's saved by Enisi guidance.
In the center of the Sphere is what appears to be a concentrated source of energy somewhat resembling a small star. The Sphere is a combination of mechanical and organic systems, and has the power to manipulate gravity inside of itself and alter space (as demonstrated in the maze puzzle and in the numerous small storage boxes that, when entered, lead to entire rooms). Various walkways allow the occupants to walk on surfaces otherwise designated as walls and ceilings. Switches that change the direction of gravity, effectively changing the orientation of anyone in the area, are present in some locations, causing floors, walls, and ceilings to change their roles depending on the switch used. The Sphere also has the ability to produce portals to other sections at will. These portals allow occupants to move much faster around the Sphere and fulfill their duties more efficiently.