planetary engineering

{{Main|Terraforming}}

File:SRMtemperature-projections.jpg

File:Terraforming_of_Mars.jpg

Terraforming is the process of modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body in order to replicate the environment of Earth.

A common object of discussion on potential terraforming is the planet Mars. To terraform Mars, humans would need to create a new atmosphere, due to the planet's high carbon dioxide concentration and low atmospheric pressure. This would be possible by introducing more greenhouse gases to below "freezing point from indigenous materials".{{cite book |last1=Pollack |first1=James B. |last2=Sagan |first2=Carl |chapter=Planetary engineering |pages=921–950 |chapter-url=http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources33.pdf |archive-url=https://web.archive.org/web/20100624205541/http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources33.pdf |archive-date=24 June 2010 |editor1-last=Lewis |editor1-first=John S. |editor2-last=Matthews |editor2-first=Mildred Shapley |editor3-last=Guerrieri |editor3-first=Mary L. |title=Resources of Near-Earth Space |date=1993 |publisher=University of Arizona Press |isbn=978-0-8165-1404-5 }} To terraform Venus, carbon dioxide would need to be converted to graphite since Venus receives twice as much sunlight as Earth. This process is only possible if the greenhouse effect is removed with the use of "high-altitude absorbing fine particles" or a sun shield, creating a more habitable Venus.

NASA has defined categories of habitability systems and technologies for terraforming to be feasible.{{Cite web |title=Habitats, Habitability, and Human Factors |url=https://sbir.nasa.gov/content/habitats-habitability-and-human-factors |access-date=5 November 2021 |website=NASA SBIR & STTR Program |archive-date=27 October 2021 |archive-url=https://web.archive.org/web/20211027102422/https://sbir.nasa.gov/content/habitats-habitability-and-human-factors |url-status=live }} These topics include creating power-efficient systems for preserving and packaging  food for crews, preparing and cooking foods, dispensing water, and developing facilities for rest, trash and recycling, and areas for crew hygiene and rest.

A variety of planetary engineering challenges stand in the way of terraforming efforts. The atmospheric terraforming of Mars, for example, would require "significant quantities of gas" to be added to the Martian atmosphere.{{cite journal |last1=Jakosky |first1=Bruce M. |last2=Edwards |first2=Christopher S. |title=Inventory of {{CO2}} available for terraforming Mars |journal=Nature Astronomy |date=August 2018 |volume=2 |issue=8 |pages=634–639 |doi=10.1038/s41550-018-0529-6 |bibcode=2018NatAs...2..634J |s2cid=133894463 }} This gas has been thought to be stored in solid and liquid form within Mars' polar ice caps and underground reservoirs. It is unlikely, however, that enough {{CO2}} for sufficient atmospheric change is present within Mars' polar deposits, and liquid {{CO2}} could only be present at warmer temperatures "deep within the crust". Furthermore, sublimating the entire volume of Mars' polar caps would increase its current atmospheric pressure to 15 millibar, where an increase to around 1000 millibar would be required for habitability. For reference, Earth's average sea-level pressure is 1013.25 mbar.

First formally proposed by astrophysicist Carl Sagan, the terraforming of Venus has since been discussed through methods such as organic molecule-induced carbon conversion, sun reflection, increasing planetary spin, and various chemical means.{{cite journal | last1 = Fogg | first1 = M. J. | year = 1987 | title = The Terraforming of Venus | journal = Journal of the British Interplanetary Society | volume = 40 | pages = 551–564 | bibcode=1987JBIS...40..551F}} Due to the high presence of sulfuric acid and solar wind on Venus, which are harmful to organic environments, organic methods of carbon conversion have been found unfeasible. Other methods, such as solar shading, hydrogen bombardment, and magnesium-calcium bombardment are theoretically sound but would require large-scale resources and space technologies not yet available to humans.

While successful terraforming would allow life to prosper on other planets, philosophers have debated whether this practice is morally sound. Certain ethics experts suggest that planets like Mars hold an intrinsic value independent of their utility to humanity and should therefore be free from human interference.{{Cite web |title=The Ethics of Terraforming {{!}} Issue 38 |url=https://philosophynow.org/issues/38/The_Ethics_of_Terraforming |access-date=5 November 2021 |website=Philosophy Now |archive-date=5 November 2021 |archive-url=https://web.archive.org/web/20211105014517/https://philosophynow.org/issues/38/The_Ethics_of_Terraforming |url-status=live }} Also, some argue that through the steps that are necessary to make Mars habitable - such as fusion reactors, space-based solar-powered lasers, or spreading a thin layer of soot on Mars' polar ice caps - would deteriorate the current aesthetic value that Mars possesses.{{cite journal |last1=Sparrow |first1=Robert |title=The Ethics of Terraforming |journal=Environmental Ethics |date=Fall 1999 |volume=21 |issue=3 |pages=227–245 |doi= 10.1007/978-90-481-9920-4_124 |url=https://robsparrow.com/wp-content/uploads/The-ethics-of-terraforming.pdf |access-date=April 21, 2023}} This calls into question humanity's intrinsic ethical and moral values, as it raises the question of whether humanity is willing to eradicate the current ecosystem of another planet for their benefit.{{cite journal |last1=Sparrow |first1=Robert |title=The Ethics of Terraforming |journal=Environmental Ethics |date=Fall 1999 |volume=21 |issue=3 |pages=227–245 |doi=10.1007/978-90-481-9920-4_124 |url=https://robsparrow.com/wp-content/uploads/The-ethics-of-terraforming.pdf |access-date=April 21, 2023}} Through this ethical framework, terraforming attempts on these planets could be seen to threaten their intrinsically valuable environments, rendering these efforts unethical.

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Mars is the primary subject of discussion for seeding. Locations for seeding are chosen based on atmospheric temperature, air pressure, existence of harmful radiation, and availability of natural resources, such as water and other compounds essential to terrestrial life.{{cite journal |last1=Todd |first1=Paul |title=Planetary biology and terraforming |journal=Gravitational and Space Biology |date=August 2006 |volume=19 |issue=2 |pages=79–85 |id={{Gale|A176373142}} |url=http://gravitationalandspaceresearch.org/index.php/journal/article/view/11 }}

Natural or engineered microorganisms must be created or discovered that can withstand the harsh environments of Mars. The first organisms used must be able to survive exposure to ionizing radiation and the high concentration of {{CO2}} present in the Martian atmosphere. Later organisms such as multicellular plants must be able to withstand the freezing temperatures, withstand high {{CO2}} levels, and produce significant amounts of {{chem2|O2}}.

Microorganisms provide significant advantages over non-biological mechanisms. They are self-replicating, negating the needs to either transport or manufacture large machinery to the surface of Mars. They can also perform complicated chemical reactions with little maintenance to realize planet-scale terraforming.{{cite journal |last1=Conde-Pueyo |first1=Nuria |last2=Vidiella |first2=Blai |last3=Sardanyés |first3=Josep |last4=Berdugo |first4=Miguel |last5=Maestre |first5=Fernando T. |last6=de Lorenzo |first6=Victor |last7=Solé |first7=Ricard |title=Synthetic Biology for Terraformation Lessons from Mars, Earth, and the Microbiome |journal=Life |date=9 February 2020 |volume=10 |issue=2 |page=14 |doi=10.3390/life10020014 |pmid=32050455 |pmc=7175242 |doi-access=free |bibcode=2020Life...10...14C }}

{{Main|Climate engineering}}

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Climate engineering is a form of planetary engineering which involves the process of deliberate and large-scale alteration of the Earth's climate system to combat climate change.{{Cite web|title=What is Climate Engineering?|url=https://www.ucsusa.org/resources/what-climate-engineering|access-date=27 October 2021|website=Union of Concerned Scientists|language=en|archive-date=27 October 2021|archive-url=https://web.archive.org/web/20211027225649/https://www.ucsusa.org/resources/what-climate-engineering|url-status=live}} Examples of geoengineering are carbon dioxide removal (CDR), which removes carbon dioxide from the atmosphere, and solar radiation modification (SRM) to reflect solar energy to space.{{Cite web|date=9 May 2018|title=Explainer: Six ideas to limit global warming with solar geoengineering|url=https://www.carbonbrief.org/explainer-six-ideas-to-limit-global-warming-with-solar-geoengineering|access-date=1 November 2021|website=Carbon Brief|language=en|archive-date=1 November 2021|archive-url=https://web.archive.org/web/20211101225428/https://www.carbonbrief.org/explainer-six-ideas-to-limit-global-warming-with-solar-geoengineering|url-status=live}} Carbon dioxide removal (CDR) has multiple practices, the simplest being reforestation, to more complex processes such as direct air capture.{{Cite web|title=Effectively removing {{CO2}} from the atmosphere|url=https://www.sciencedaily.com/releases/2021/08/210813100255.htm|access-date=27 October 2021|website=ScienceDaily|language=en|archive-date=27 October 2021|archive-url=https://web.archive.org/web/20211027230911/https://www.sciencedaily.com/releases/2021/08/210813100255.htm|url-status=live}} The latter is rather difficult to deploy on an industrial scale, for high costs and substantial energy usage would be some aspects to address.

Examples of SRM include stratospheric aerosol injection (SAI) and marine cloud brightening (MCB). When a volcano erupts, small particles known as aerosols proliferate throughout the atmosphere, reflecting the sun's energy back into space.{{Cite web|title=Volcanoes Can Affect Climate|url=https://www.usgs.gov/natural-hazards/volcano-hazards/volcanoes-can-affect-climate|access-date=1 November 2021|website=USGS|archive-date=31 October 2021|archive-url=https://web.archive.org/web/20211031123358/https://www.usgs.gov/natural-hazards/volcano-hazards/volcanoes-can-affect-climate|url-status=live}} This results in a cooling effect, and humanity could conceivably inject these aerosols into the stratosphere, spurring large-scale cooling.

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One proposal for MCB involves spraying a vapor into low-laying sea clouds, creating more cloud condensation nuclei.{{Cite web|title=Proposed Geoengineering Technologies|url=https://www.geoengineeringmonitor.org/technologies/|access-date=3 November 2021|website=Geoengineering Monitor|language=en-US|archive-date=3 November 2021|archive-url=https://web.archive.org/web/20211103232453/https://www.geoengineeringmonitor.org/technologies/|url-status=live}} This would in theory result in the cloud becoming whiter, and reflecting light more efficiently.

• Astroengineering
• Macro-engineering
• Megascale engineering
• Moving the Earth
• Virgin Earth Challenge

{{Reflist}}

• {{cite encyclopedia|last=Angelo|first=Joseph A. Jr. |title=Planetary engineering |encyclopedia=Encyclopedia of space and astronomy|pages=462–462|year=2006|publisher=Facts On File|location=New York |isbn=978-1-4381-1018-9 }}
• {{cite journal |last1=Sagan |first1=Carl |title=Planetary engineering on Mars |journal=Icarus |date=December 1973 |volume=20 |issue=4 |pages=513–514 |doi=10.1016/0019-1035(73)90026-2 |bibcode=1973Icar...20..513S }}

{{Portal|Energy}}

• [https://web.archive.org/web/20150911231528/http://www.worldchanging.com/archives//008364.html Geoengineering: A Worldchanging Retrospective] – Overview of articles on geoengineering from the sustainability site Worldchanging

{{Engineering fields}}

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Category:Space colonization

Category:Engineering disciplines