Editing Terraforming (section)

===Venus===
{{main|Terraforming of Venus}}
[[File:Venus-real color.jpg|thumb|True-color image of Venus. To terraform, this dense atmosphere will need to be removed.|left|200x200px]]Terraforming [[Venus]] requires two major changes: removing most of the planet's dense {{cvt|9|MPa|psi atm}} carbon dioxide atmosphere, and reducing the planet's {{cvt|450|C}} surface temperature.<ref name="fogg1987">{{cite journal |bibcode=1987JBIS...40..551F |title=The terraforming of Venus |journal=Journal of the British Interplanetary Society |volume=40 |pages=551 |last1=Fogg |first1=M. J. |year=1987 }}</ref><ref name="Landis2011">{{cite book |doi=10.2514/6.2011-7215 |chapter=Terraforming Venus: A Challenging Project for Future Colonization |title=AIAA SPACE 2011 Conference & Exposition |year=2011 |last1=Landis |first1=Geoffrey |isbn=978-1-60086-953-2 }}</ref> These goals are closely interrelated because Venus's extreme temperature may result from the [[greenhouse effect]] caused by its dense atmosphere. 
[[File:TerraformedVenus.jpg|thumb|right|210px|Artist's conception of a terraformed [[Venus]]]]

Venus's atmosphere currently contains little oxygen, so an additional step would be to inject breathable O<sub>2</sub> into the atmosphere. An early proposal for such a process comes from [[Carl Sagan]], who suggested the injection of floating, [[Photosynthesis|photosynthetic]] bacteria into the Venusian atmosphere to reduce CO<sub>2</sub> to [[Organic carbon|organic form]], and increase the atmospheric concentration of O<sub>2</sub> in the atmosphere.<ref name="The Planet Venus" /> This concept, however, was based in a flawed 1960s understanding of Venus's atmosphere as much lower pressure; in reality, the Venusian atmospheric pressure (9300 kPa) is far higher than early estimates. Sagan's idea is therefore untenable, as he later conceded.<ref>{{Cite book |last=Sagan |first=Carl |url=https://www.worldcat.org/oclc/30736355 |title=Pale blue dot : a vision of the human future in space |date=1994 |isbn=0-679-76486-0 |edition=First |location=New York |oclc=30736355}}</ref>

An additional step noted by Martin Beech includes the injection of water and/or hydrogen into the planetary atmosphere;<ref name=":0" /> this step follows after sequestering CO<sub>2</sub> and reducing the mass of the atmosphere. In order to combine hydrogen with O<sub>2</sub> produced by other means, an estimated 4×10<sup>19</sup> kg of hydrogen is necessary; this may need to be mined from another source, such as Uranus or Neptune.<ref name=":0" />