The game was expected to take place on Exodus, which was an alien planet where Killian Samuels worked as a bounty hunter. Exodus is tidally locked, meaning that one side of the planet is always facing the sun, and the other always facing away. Although the planet itself revolves around a sun-like star the actual planet itself does not spin, meaning that the planet is composed of three distinct areas of light, roughly equivalent to daylight, dusk and night-time. In the final games these three areas will act as various hubs for the missions you take on.
Exodus' atmosphere is likely breathable to humans as both Killian and Tommy could breathe without the need of any breathing masks.
