Floating city (science fiction)

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In science fiction, floating cities are settlements that use buoyancy to remain in the atmosphere of a planet. Buckminster Fuller first proposed the concept for Earth, by building a geodesic sphere that would be heated by sunlight, and float. A similar design would permit settlers to live on Venus, where at ground level the temperature is too hot and the atmospheric pressure too great. It would also permit settlement of the outer three gas giants, as all the gas giants lack solid surfaces. The main industry of floating cities in gas giants might be to extract Helium-3 or other useful materials from their atmospheres. Jupiter is unacceptable for habitation due to its high gravity, escape velocity and radiation, but the solar system's other gas giants (Saturn, Uranus, and Neptune) are more practical.

The easiest planet to place floating cities at this point would appear to be Venus. The thick carbon dioxide atmosphere is significantly denser than air, which means that any large structure filled with air (molecular nitrogen and oxygen) would float on the carbon dioxide, with the air's natural buoyancy counteracting the weight of the structure itself. The main challenge would be using a substance resistant to sulfuric acid to serve as the structure's outer layer; ceramics or metal sulfates could possibly serve in this role. (The sulfuric acid itself may prove to be the main motivation for creating the structure in the first place, as the acid has proven to be extremely useful for many different purposes.)