Terrarium (space habitat)
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Asteroid terraria are fictional space habitats described in the hard science fiction novel 2312 (2012) by Kim Stanley Robinson. In the novel, a 'terrarium' is an artificially created ecosystem living in the cylindrically shaped hollow interior of an asteroid. This hollow space is crafted with self replicating machine excavators. On the inner surface of this hollow cylinder an ecosystem can thrive in artificial gravity resulting from centripetal force, produced by spinning the asteroid on its longest axis. At least 2 kilometers of solid asteroid wall are left at all points around the hollow interior to provide radiation shielding and protection from interplanetary material, except at the entry hole. A lighting element, called a 'sunline', is strung inside the cylinder along the axis of rotation to provide artificial light. The lit part of the line travels the length of the cylinder to simulate the Sun’s path over Earth’s sky. During night phase, street lights, on the inner surface overhead, resemble stars.
Robinson writes about the infinite possibilities for terraria ecosystems, e.g. savannas, water worlds, genetically engineered ecospheres or habitats with new species, called 'Ascensions', resulting from the hybridization of common ones. Terraria are not only created for residential purposes; in 2312 they also function as farming worlds (producing food for Earth) and transportation vessels. Propelled through the solar system, they follow regular routes, non-stop, like unclaimed asteroids do. Ferries wishing to board them need to match their speeds. Terraria make travel from Earth to the outer planets a matter of weeks, like did transatlantic voyages before the steam engine. In the novel, the Alfred Wegener (presumably named after a German geophysicist) is one such terrarium, in an excavated cylinder twenty kilometers long and five across:
Grass prairie and patches of forest arched like a giant Sistine Chapel overhead, a Sistine on which Michelangelo had painted a version of Eden—a savanna, the first human landscape, appealing to something very deep in the mind. Although terrarium topology always made Wahram feel as if he were inside a map that had been rolled into a tube.