Terraforming

Terraforming (literally, "Earth-shaping") is the process of modifying a planet, moon or other body to a more habitable atmosphere, temperature or ecology.

Table of contents
1 History
2 Theoretical Methods of Terraforming
3 Paraterraforming
4 Geoengineering

History

In fiction

The term first appeared in a science fiction novel, Seetee Shock (1949) by Jack Williamson, but the actual concept pre-dates this work. Olaf Stapledon's First and Last Men (1930) provides an example in fiction in which Venus is modified, after a long and destructive war with the original inhabitants, who naturally object to the process. Early fictional accounts of the process are frequently handicapped by the inaccurate contemporary knowledge of the actual conditions, as in the Stapledon example, which had Venus covered in oceans.

A more recent example, using the actual conditions on Mars as revealed by planetary probes to that time, is the Mars trilogy by Kim Stanley Robinson. The three volumes provide a lengthy description of a fictional terraforming of Mars, and very evidently result from a massive amount of research by the author.

Scholarly study

In the 1960s the astronomer and popularizer of science Carl Sagan proposed terraforming the planet Venus by seeding its atmosphere with algae, which would remove carbon dioxide and reduce the greenhouse effect until surface temperatures dropped to "comfortable" levels. Later discoveries about the conditions on Venus made this particular approach impossible, however: Venus simply has too much atmosphere to process and sequester. Even if atmospheric algae could thrive in the hostile and arid environment of Venus' upper atmosphere, any carbon that was fixed in organic form would be liberated as carbon dioxide again as soon as it fell into the hot lower regions.

Today Mars seems the most feasible local planet for terraforming. Robert Zubrin, the founder of the Mars Society, has presented a well-elaborated plan for this. He wants to start with a Mars return mission called Mars Direct.

The principal reason given to pursue terraforming is the creation of worlds suitable for habitation by human beings and of an ecology to support them. However, some researchers believe that space habitats will provide a more economical means for supporting space colonization.

If research in nanotechnology and other advanced chemical processes continues apace, it may become feasible to terraform planets in centuries rather than millennia. On the other hand, it may become reasonable to modify humans so that they don't require an oxygen/nitrogen atmosphere in a 1g gravity field to live comfortably. That would then reduce the need to terraform worlds, or at least the degree to which other worlds' environments would need to be altered.

Theoretical Methods of Terraforming

Mars

There is some scientific debate over whether it would even be possible to terraform Mars, or how stable its climate would be once terraformed. It is possible that over geological timescales - tens or hundreds of millions of years - Mars could lose its water and atmosphere again, possibly to the same processes that reduced it to its current state.

Venus

  • Solar shades placed in the Sun-Venus L1 point or in a more closely-orbiting ring to reduce the total insolation received by Venus (this does not directly deal with the immense atmospheric density of Venus, but could make it easier to do so by other methods).
  • Bombardment of Venus with refined magnesium and calcium metal from Mercury or some other source, to sequester carbon dioxide in the form of calcium and magnesium carbonates.

(This needs a lot more yet, including non-fictional research)

Paraterraforming

Also known as the "worldhouse" concept, paraterraforming involves the construction of a habitable enclosure on a planet which eventually grows to encompass most of the planet's useable 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. A worldhouse can be constructed with technology known since the 1960s.

Paraterraforming has several advantages over the traditional approach to terraforming. For example, it provides an immediate payback to investors; the worldhouse starts out small in area, but those areas provide habitable space from the start. 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 in order to provide Earthlike 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.

Geoengineering

Geoengineering is the deliberate modification of Earth's environment on a large scale, in a sense "terraforming" Earth itself. Currently a great deal of debate takes place over the notion that human civilization has already inadvertantly modified Earth's climate through the industrial emission of greenhouse gases, and proposals have been made to counter any such effects through further deliberate geoengineering. For example, some have proposed to put large mirrors in orbit which would modify the insolation received by Earth - either increasing or decreasing it, as the need arises. Large-scale sequestration of carbon dioxide inside geological formations or ocean sediment, modification of Earth's albedo with reflective or absorbtive materials spread over portions of its surface, or the alteration of rainfall patterns through the creation of artificial seas are other examples which have been seriously considered.




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