A large part of the series mythology in the second season is the World Engines, a propulsion system built into the planets of the Cluster (and presumably many other worlds, since two different planets in different solar systems have them) by an ancient alien race. Using five mountain-sized energy thrusters which emerge from the planet's surface, the World Engines can propel a planet through space at great speeds. A combination of an atmospheric shield and artificial gravity generators keep the sudden shift in orbit and lack of a star from killing everyone on the surface. The Prison Planet has a variation known as Teleport Engines, which teleport the world to different locations in space instantly. The same artificial gravity and atmospheric shielding technology is used to protect the inhabitants. Each set of engines is located at the core of its world and can be reached using Telepods, small platforms on the surface of each world. The Telepods send the user to the core of the planet where they can use the computer to move the planet. The Telepods can also be used to move people from one planet to another.