The series takes place in the year 2517, on several planets and moons. The television series does not say if these are in one star system. The movie "Serenity" makes clear that all the planets and moons are in one large system. The characters refer to "Earth-that-was" and in the movie, it is said that long before the events in the series a large population had left from Earth to a new star system: "Earth that was could no longer sustain our numbers, we were so many." The people settled in this new star system, with "dozens of planets and hundreds of moons." Many of these were terraformed, a process in which a planet or moon is altered to resemble the Earth. The terraforming process was only the first step in making a planet livable. Only the most central planets got more treatment. This caused many of the border planets and moons to have environments that fit the Western setting.