 The series takes place in the year 2517 , on a variety of planets and moons . The TV series does not reveal whether these celestial bodies are within one star system , only saying that Serenity 's mode of propulsion is a " gravity @-@ drive " . The film Serenity makes clear that all the planets and moons are in one large system , and production documents related to the film indicate that there is no faster @-@ than @-@ light travel in this universe . The characters occasionally refer to " Earth @-@ that @-@ was " , and the film establishes that , long before the events in the series , a large population had emigrated from Earth to a new star system in generation ships : " Earth @-@ that @-@ was could no longer sustain our numbers , we were so many " . The emigrants established themselves 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 Earth . The terraforming process was only the first step in making a planet habitable , however , and the outlying settlements often did not receive any further support in the construction of their civilizations . This resulted in many of the border planets and moons having forbidding , dry environments , well @-@ suited to the Western genre . 
