Title: Terraforming - Wikipedia
Headings: Terraforming
Terraforming
Contents
History of scholarly study
Aspects and definitions
Habitability requirements
Preliminary stages
Prospective targets
Mars
Venus
Mercury
Moon
Earth
Other bodies in the Solar System
Other possibilities
Biological terraforming
Paraterraforming
Adapting humans
Issues
Ethical issues
Economic issues
Political issues
In popular culture
See also
Notes
References
External links

Content: If initially lifeless, then such a world could host a biosphere of considerable complexity without the need for terraforming. Easily Terraformable Planet (ETP): A planet that might be rendered biocompatible, or possibly habitable, and maintained so by modest planetary engineering techniques and with the limited resources of a starship or robot precursor mission. Fogg suggests that Mars was a biologically compatible planet in its youth, but is not now in any of these three categories, because it can only be terraformed with greater difficulty. Habitability requirements
Main article: Planetary habitability
An absolute requirement for life is an energy source, but the notion of planetary habitability implies that many other geophysical, geochemical, and astrophysical criteria must be met before the surface of an astronomical body is able to support life. Of particular interest is the set of factors that has sustained complex, multicellular animals in addition to simpler organisms on Earth. Research and theory in this regard is a component of planetary science and the emerging discipline of astrobiology . In its astrobiology roadmap, NASA has defined the principal habitability criteria as "extended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy sources to sustain metabolism ." Preliminary stages
Once conditions become more suitable for life of the introduced species, the importation of microbial life could begin.