Editing Terraforming (section)

==Preliminary stages==
{{Multiple issues|section=yes|{{Expand section|date=December 2022}}}}
Terraforming a planet would involve making it fit the habitability requirements listed in the previous section. For example, a planet may be too cold for liquid water to exist on its surface. Its temperature could be raised by adding greenhouse gases to the atmosphere,<ref>{{cite journal |last1=Gerstell |first1=M. F. |last2=Francisco |first2=J. S. |last3=Yung |first3=Y. L. |last4=Boxe |first4=C. |last5=Aaltonee |first5=E. T. |date=27 February 2001 |title=Keeping Mars warm with new super greenhouse gases |journal=Proceedings of the National Academy of Sciences |volume=98 |issue=5 |pages=2154–2157 |bibcode=2001PNAS...98.2154G |doi=10.1073/pnas.051511598 |pmc=30108 |pmid=11226208 |doi-access=free}}</ref> using orbiting mirrors to reflect more sunlight onto the planet,<ref>{{Citation |last=McInnes |first=Colin R. |title=Mars Climate Engineering Using Orbiting Solar Reflectors |date=2009 |url=http://link.springer.com/10.1007/978-3-642-03629-3_25 |work=Mars |pages=645–659 |editor-last=Badescu |editor-first=Viorel |access-date=2023-12-07 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-642-03629-3_25 |isbn=978-3-642-03628-6}}</ref> or lowering the [[albedo]] of the planet.<ref name=":3" /> Conversely, a planet too hot for liquid water could be cooled down by removing greenhouse gases (if these are present), placing a sunshade in the [[Lagrange point|L<sub>1</sub> point]] to reduce sunlight reaching the planet, or increasing the albedo.<ref name="Landis2011"/>
Atmospheric pressure is another issue: various celestial bodies including Mars, Mercury and most moons have lower pressure than Earth. At pressures below the [[triple point of water]] (611.7 Pa), water cannot be liquid at any temperature. Human survival requires a still-higher pressure of at least 6.3 kPa, the [[Armstrong limit]]; below this pressure, exposed body fluids boil at body temperature. Furthermore, a thick atmosphere protects the surface from [[cosmic ray]]s.<ref name=":4">{{Cite web |title=Cosmic Radiation |url=https://www.epa.gov/radtown/cosmic-radiation |access-date=December 8, 2023 |website=epa.gov|date=27 November 2018 }}</ref> A thin atmosphere could be thickened using gases produced locally (e.g. the Moon could be given an atmosphere of oxygen by reducing lunar rock<ref name="landis1990" />) or gases could be imported from elsewhere.

Once conditions become more suitable for [[life]] of the [[introduced species]], the importation of [[microbial]] life could begin.<ref name="EPE" /> As conditions approach that of Earth, [[plants|plant life]] could also be brought in. This would accelerate the production of oxygen, which theoretically would make the planet eventually able to support [[animal]] life.