This category is for those celestial bodies (planets , minor planets , moons , exoplanets , etc.) that simply may be too small, hot, cold, or lacking in a magnetic field that letting it hold on to an atmosphere alone is not practical. These objects are often not massive enough for its gravity to hold onto gases for very long. The "solar wind" can easily strip an atmosphere, even if enough gravity is present, or vice versa, and its radiation is damaging to life. If the body is outside the habitable zone, the heat alone can blowtorch the atmosphere and water away, or in the cold, freeze it solid to the surface. Paraterraforming could solve these problems by negating the need for a strong gravitational field, insolating the surface volatiles, and possibly blocking out radiation, or at least keep it from escaping (though ionization could still be a problem). A way to solve that is through magnetic field-inducing artificial satellites, but that is not specifically necessary to paraterraforming.
Also known as the "worldhouse" concept, or domes in smaller versions, paraterraforming involves the construction of a habitable enclosure on a planet which eventually grows to encompass most of the planet's usable area. The enclosure would consist of a transparent roof held one or more kilometers above the surface, pressurized with a breathable atmosphere, and anchored with tension towers and cables at regular intervals. Proponents claim worldhouses can be constructed with technology known since the 1960s. The Biosphere 2 project built a dome on Earth that contained a habitable environment. The project encountered difficulties in construction and operation.
Paraterraforming has several advantages over the traditional approach to terraforming. For example, it provides an immediate payback to investors (assuming a capitalistic financing model). Although it starts out in a small area (a domed city for example), it quickly provides habitable space. The paraterraforming approach also allows for a modular approach that can be tailored to the needs of the planet's population, growing only as fast and only in those areas where it is required. Finally, paraterraforming greatly reduces the amount of atmosphere that one would need to add to planets like Mars to provide Earth-like atmospheric pressures. By using a solid envelope in this manner, even bodies which would otherwise be unable to retain an atmosphere at all (such as asteroids) could be given a habitable environment. The environment under an artificial worldhouse roof would also likely be more amenable to artificial manipulation.Paraterraforming is also less likely to cause harm to any native lifeforms that may hypothetically inhabit the planet, as the parts of the planet outside the enclosure will not normally be affected unlike terraforming which affects the entire planet.
It has the disadvantage of requiring massive amounts of construction and maintenance activity. It also would not likely have a completely independent water cycle, because although rainfall may be able to develop with a high enough roof, but probably not efficiently enough for agriculture or a water cycle. The extra cost might be off-set somewhat by automated manufacturing and repair mechanisms. A worldhouse might also be more susceptible to catastrophic failure if a major breach occurred, though this risk might be reduced by compartmentalization and other active safety precautions. Meteor strikes are a particular concern because without any external atmosphere they would reach the surface before burning up.
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