Terraforming

Terraforming or terraformation (literally, "Earth-shaping") of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, temperature, surface topography or ecology to be similar to the environment of Earth to make it habitable by Earth-like life.

The concept of terraforming developed from both science fiction and actual science. The term was coined by Jack Williamson in a science-fiction short story ("Collision Orbit") published during 1942 in Astounding Science Fiction,[1] but the concept may pre-date this work.

Even if the environment of a planet could be altered deliberately, the feasibility of creating an unconstrained planetary environment that mimics Earth on another planet has yet to be verified. Mars is usually considered to be the most likely candidate for terraforming. Much study has been done concerning the possibility of heating the planet and altering its atmosphere, and NASA has even hosted debates on the subject. Several potential methods of altering the climate of Mars may fall within humanity's technological capabilities, but at present the economic resources required to do so are far beyond that which any government or society is willing to allocate to it. The long timescales and practicality of terraforming are the subject of debate. Other unanswered questions relate to the ethics, logistics, economics, politics, and methodology of altering the environment of an extraterrestrial world.

MarsTransitionV
An artist's conception shows a terraformed Mars in four stages of development.

History of scholarly study

The renowned astronomer Carl Sagan proposed the planetary engineering of Venus in an article published in the journal Science in 1961.[2] Sagan imagined seeding the atmosphere of Venus with algae, which would convert water, nitrogen and carbon dioxide into organic compounds. As this process removed carbon dioxide from the atmosphere, the greenhouse effect would be reduced until surface temperatures dropped to "comfortable" levels. The resulting carbon, Sagan supposed, would be incinerated by the high surface temperatures of Venus, and thus be sequestered in the form of "graphite or some involatile form of carbon" on the planet's surface.[3] However, later discoveries about the conditions on Venus made this particular approach impossible. One problem is that the clouds of Venus are composed of a highly concentrated sulfuric acid solution. Even if atmospheric algae could thrive in the hostile environment of Venus's upper atmosphere, an even more insurmountable problem is that its atmosphere is simply far too thick—the high atmospheric pressure would result in an "atmosphere of nearly pure molecular oxygen" and cause the planet's surface to be thickly covered in fine graphite powder.[3] This volatile combination could not be sustained through time. Any carbon that was fixed in organic form would be liberated as carbon dioxide again through combustion, "short-circuiting" the terraforming process.[3]

Sagan also visualized making Mars habitable for human life in "Planetary Engineering on Mars" (1973), an article published in the journal Icarus.[4] Three years later, NASA addressed the issue of planetary engineering officially in a study, but used the term "planetary ecosynthesis" instead.[5] The study concluded that it was possible for Mars to support life and be made into a habitable planet. The first conference session on terraforming, then referred to as "Planetary Modeling", was organized that same year.

In March 1979, NASA engineer and author James Oberg organized the First Terraforming Colloquium, a special session at the Lunar and Planetary Science Conference in Houston. Oberg popularized the terraforming concepts discussed at the colloquium to the general public in his book New Earths (1981).[6] Not until 1982 was the word terraforming used in the title of a published journal article. Planetologist Christopher McKay wrote "Terraforming Mars", a paper for the Journal of the British Interplanetary Society.[7] The paper discussed the prospects of a self-regulating Martian biosphere, and McKay's use of the word has since become the preferred term. In 1984, James Lovelock and Michael Allaby published The Greening of Mars.[8] Lovelock's book was one of the first to describe a novel method of warming Mars, where chlorofluorocarbons (CFCs) are added to the atmosphere.

Motivated by Lovelock's book, biophysicist Robert Haynes worked behind the scenes to promote terraforming, and contributed the neologism Ecopoiesis,[9] forming the word from the Greek οἶκος, oikos, "house",[10] and ποίησις, poiesis, "production".[11] Ecopoiesis refers to the origin of an ecosystem. In the context of space exploration, Haynes describes ecopoiesis as the "fabrication of a sustainable ecosystem on a currently lifeless, sterile planet". Fogg defines ecopoiesis as a type of planetary engineering and is one of the first stages of terraformation. This primary stage of ecosystem creation is usually restricted to the initial seeding of microbial life.[12] As conditions approach that of Earth, plant life could be brought in, and this will accelerate the production of oxygen, theoretically making the planet eventually able to support animal life.

Aspects and definitions

Beginning in 1985, Martyn J. Fogg started publishing several articles on terraforming. He also served as editor for a full issue on terraforming for the Journal of the British Interplanetary Society in 1992. In his book Terraforming: Engineering Planetary Environments (1995), Fogg proposed the following definitions for different aspects related to terraforming:[12]

  • Planetary engineering: the application of technology for the purpose of influencing the global properties of a planet.
  • Geoengineering: planetary engineering applied specifically to Earth. It includes only those macroengineering concepts that deal with the alteration of some global parameter, such as the greenhouse effect, atmospheric composition, insolation or impact flux.
  • Terraforming: a process of planetary engineering, specifically directed at enhancing the capacity of an extraterrestrial planetary environment to support life as we know it. The ultimate achievement in terraforming would be to create an open planetary ecosystem emulating all the functions of the biosphere of Earth, one that would be fully habitable for human beings.

Fogg also devised definitions for candidate planets of varying degrees of human compatibility:[13]

  • Habitable Planet (HP): A world with an environment sufficiently similar to Earth as to allow comfortable and free human habitation.
  • Biocompatible Planet (BP): A planet possessing the necessary physical parameters for life to flourish on its surface. 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.[14]

Habitability requirements

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."[15]

Preliminary stages

Once conditions become more suitable for life of the introduced species, the importation of microbial life could begin.[12] As conditions approach that of Earth, 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.

Prospective targets

TerraformedMars
Artist's conception of a terraformed Mars

Mars

In many respects, Mars is the most Earth-like planet in the Solar System.[16] It is thought that Mars once had a more Earth-like environment early in its history, with a thicker atmosphere and abundant water that was lost over the course of hundreds of millions of years.[17]

The exact mechanism of this loss is still unclear, though three mechanisms in particular seem likely: First, whenever surface water is present, carbon dioxide (CO
2
) reacts with rocks to form carbonates, thus drawing atmosphere off and binding it to the planetary surface. On Earth, this process is counteracted when plate tectonics works to cause volcanic eruptions that vent carbon dioxide back to the atmosphere. On Mars, the lack of such tectonic activity worked to prevent the recycling of gases locked up in sediments.[18]

Second, the lack of a magnetosphere around Mars may have allowed the solar wind to gradually erode the atmosphere.[18] Convection within the core of Mars, which is made mostly of iron,[19] originally generated a magnetic field. However the dynamo ceased to function long ago,[20] and the magnetic field of Mars has largely disappeared, probably due to "... loss of core heat, solidification of most of the core, and/or changes in the mantle convection regime."[21] Results from the NASA MAVEN mission show that the atmosphere is removed primarily due to Coronal Mass Ejection events, where outbursts of high-velocity protons from the sun impact the atmosphere. Mars does still retain a limited magnetosphere that covers approximately 40% of its surface. Rather than uniformly covering and protecting the atmosphere from solar wind, however, the magnetic field takes the form of a collection of smaller, umbrella-shaped fields, mainly clustered together around the planet's southern hemisphere.[22]

Finally, between approximately 4.1 and 3.8 billion years ago, asteroid impacts during the Late Heavy Bombardment caused significant changes to the surface environment of objects in the Solar System. The low gravity of Mars suggests that these impacts could have ejected much of the Martian atmosphere into deep space.[23]

Terraforming Mars would entail two major interlaced changes: building the atmosphere and heating it.[24] A thicker atmosphere of greenhouse gases such as carbon dioxide would trap incoming solar radiation. Because the raised temperature would add greenhouse gases to the atmosphere, the two processes would augment each other.[25] Carbon dioxide alone would not suffice to sustain a temperature above the freezing point of water, so a mixture of specialized greenhouse molecules might be manufactured.[26]

TerraformedVenus
Artist's conception of a terraformed Venus

Venus

Terraforming Venus requires two major changes; removing most of the planet's dense 9 MPa carbon dioxide atmosphere and reducing the planet's 450 °C (723.15 K) surface temperature.[27][28] These goals are closely interrelated, because Venus's extreme temperature is thought to be due to the greenhouse effect caused by its dense atmosphere. Sequestering the atmospheric carbon would likely solve the temperature problem as well.

TerraformedMoonFromEarth
Artist's conception of what the Moon might look like terraformed

The Moon

Although the gravity on Earth's moon is too low to hold an atmosphere for geological spans of time, if given an atmosphere, it would retain the atmosphere for spans of time that are long compared to human lifespans.[29] Landis[29] and others[30][31] have thus proposed that it could be feasible to terraform the moon, although not all agree with that proposal.[32] Landis estimates that a 1 PSI atmosphere of pure oxygen on the moon would require on the order of two hundred trillion tons of oxygen, and suggests it could be produced by reducing the oxygen from an amount of lunar rock equivalent to a cube about fifty kilometers on an edge. Alternatively, he suggests that the water content of "fifty to a hundred comets" the size of Halley's comet would do the job, "assuming that the water doesn't splash away when the comets hit the moon."[29] Likewise, Benford calculates that terraforming the moon would require "about 100 comets the size of Halley's."[30]

Other bodies in the Solar System

Other possible candidates for terraforming (possibly only partial or paraterraforming) include Titan, Callisto, Ganymede, Europa, and even Mercury, Saturn's moon Enceladus, and the dwarf planet Ceres.

Other possibilities

Biological Terraforming

Many proposals for planetary engineering involve the use of genetically engineered bacteria.[33][34]

As synthetic biology matures over the coming decades it may become possible to build designer organisms from scratch that directly manufacture desired products efficiently.[35] Lisa Nip, Ph.D. candidate at the MIT Media Lab's Molecular Machines group, said that by synthetic biology, scientists could genetically engineer humans, plants and bacteria to create Earth-like conditions on another planet.[36][37]

Gary King, microbiologist at Louisiana State University studying the most extreme organisms on Earth, notes that "synthetic biology has given us a remarkable toolkit that can be used to manufacture new kinds of organisms specially suited for the systems we want to plan for" and outlines the prospects for terraforming, saying "we'll want to investigate our chosen microbes, find the genes that code for the survival and terraforming properties that we want (like radiation and drought resistance), and then use that knowledge to genetically engineer specifically Martian-designed microbes". He sees the project's biggest bottleneck in the ability to genetically tweak and tailor the right microbes, estimating that this hurdle could take "a decade or more" to be solved. He also notes that the it would be best to develop "not a single kind microbe but a suite of several that work together".[38]

DARPA is researching using photosynthesizing plants, bacteria, and algae grown directly on the Mars surface that could warm up and thicken its atmosphere. In 2015 the agency and some of its research partners have created a software called DTA GView − a 'Google Maps of genomes', in which genomes of several organisms can be pulled up on the program to immediately show a list of known genes and where they are located in the genome. According to Alicia Jackson, deputy director of DARPA's Biological Technologies Office by this they have developed a "technological toolkit to transform not just hostile places here on Earth, but to go into space not just to visit, but to stay".[39][40][41][42]

Paraterraforming

Also known as the "worldhouse" concept, paraterraforming involves the construction of a habitable enclosure on a planet which encompasses most of the planet's usable area.[43] 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. The worldhouse concept is similar to the concept of a domed habitat, but one which covers all (or most) of the planet.

Adapting humans

It has also been suggested that instead of or in addition to terraforming a hostile environment humans might adapt to these places by the use of genetic engineering, biotechnology and cybernetic enhancements.[44][45][46][47][48]

Issues

Ethical issues

There is a philosophical debate within biology and ecology as to whether terraforming other worlds is an ethical endeavor. From the point of view of a cosmocentric ethic, this involves balancing the need for the preservation of human life against the intrinsic value of existing planetary ecologies.[49]

On the pro-terraforming side of the argument, there are those like Robert Zubrin, Martyn J. Fogg, Richard L. S. Taylor and the late Carl Sagan who believe that it is humanity's moral obligation to make other worlds suitable for life, as a continuation of the history of life transforming the environments around it on Earth.[50][51] They also point out that Earth would eventually be destroyed if nature takes its course, so that humanity faces a very long-term choice between terraforming other worlds or allowing all terrestrial life to become extinct. Terraforming totally barren planets, it is asserted, is not morally wrong as it does not affect any other life.

The opposing argument posits that terraforming would be an unethical interference in nature, and that given humanity's past treatment of Earth, other planets may be better off without human interference. Still others strike a middle ground, such as Christopher McKay, who argues that terraforming is ethically sound only once we have completely assured that an alien planet does not harbor life of its own; but that if it does, we should not try to reshape it to our own use, but we should engineer its environment to artificially nurture the alien life and help it thrive and co-evolve, or even co-exist with humans.[52] Even this would be seen as a type of terraforming to the strictest of ecocentrists, who would say that all life has the right, in its home biosphere, to evolve without outside interference.

Economic issues

The initial cost of such projects as planetary terraforming would be gargantuan, and the infrastructure of such an enterprise would have to be built from scratch. Such technology is not yet developed, let alone financially feasible at the moment. John Hickman has pointed out that almost none of the current schemes for terraforming incorporate economic strategies, and most of their models and expectations seem highly optimistic.[53]

Political issues

National pride, rivalries between nations, and the politics of public relations have in the past been the primary motivations for shaping space projects.[54][55] It is reasonable to assume that these factors would also be present in planetary terraforming efforts.

In popular culture

Terraforming is a common concept in science fiction, ranging from television, movies and novels to video games.

See also

References

  1. ^ "Science Fiction Citations: terraforming". Retrieved 2006-06-16.
  2. ^ Sagan, Carl (1961). "The Planet Venus". Science. 133 (3456): 849–58. Bibcode:1961Sci...133..849S. doi:10.1126/science.133.3456.849. PMID 17789744.
  3. ^ a b c Sagan 1997, pp. 276–7.
  4. ^ Sagan, Carl (1973). "Planetary Engineering on Mars". Icarus. 20 (4): 513. Bibcode:1973Icar...20..513S. doi:10.1016/0019-1035(73)90026-2.
  5. ^ Averner& MacElroy, 1976
  6. ^ Oberg, James Edward (1981). New Earths: Restructuring Earth and Other Planets. Stackpole Books, Harrisburg, Pennsylvania.
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  8. ^ Lovelock, James & Allaby, Michael (1984). The Greening of Mars.
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  13. ^ Fogg, 1996
  14. ^ 1960-, Fogg, Martyn J., (1995). Terraforming : engineering planetary environments. Society of Automotive Engineers. ISBN 1560916095. OCLC 32348444.
  15. ^ "Goal 1: Understand the nature and distribution of habitable environments in the Universe". Astrobiology: Roadmap. NASA. Archived from the original on 2011-01-17. Retrieved 2007-08-11.
  16. ^ Read and Lewis 2004, p.16; Kargel 2004, pp. 185–6.
  17. ^ Kargel 2004, 99ff
  18. ^ a b Forget, Costard & Lognonné 2007, pp. 80–2.
  19. ^ Dave Jacqué (2003-09-26). "APS X-rays reveal secrets of Mars' core". Argonne National Laboratory. Retrieved 2009-06-10.
  20. ^ Schubert, Turcotte & Olson 2001, p. 692
  21. ^ Carr 2007, p. 318
  22. ^ Solar Wind, 2008
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  24. ^ Faure & Mensing 2007, p. 252.
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  26. ^ Gerstell, Francisco, Yung, Boxe, & Aaltonee (2001) PNAS 98, pp. 2154-7.
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  29. ^ a b c Landis, Geoffrey (1990) "Air Pollution on the Moon," Analog, June.
  30. ^ a b Benford, Greg (2014) "How to Terraform the Moon", Slate, July 14. Retrieved 30 January 2017
  31. ^ Williams, Matt (2016) "How Do We Terraform the Moon", Universe Today, 31 March. Retrieved 30 January 2017
  32. ^ Dorminey, Bruce (2016) "Why The Moon Should Never Be Terraformed", Forbes, July 27. Retrieved 30 January 2017
  33. ^ Hiscox, JA; Thomas, DJ (October 1995). "Genetic modification and selection of microorganisms for growth on Mars" (PDF). Journal of the British Interplanetary Society. 48 (10): 419–26. PMID 11541203.
  34. ^ "Mercury". The Society. The Society. 29. Retrieved 10 January 2017.
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  43. ^ Taylor, 1992
  44. ^ Gronstal, A.; Pérez, J.E.A.; Bittner, T.; Clacey, E.; Grubisic, A.; Rogers, D. (1 January 2005). "Bioforming and terraforming: A balance of methods for feasible space colonization". 2. Retrieved 10 January 2017.
  45. ^ Lunan, Duncan. Man and the Planets: The Resources of the Solar System. Ashgrove Press. ISBN 9780906798171. Retrieved 10 January 2017.
  46. ^ Spitzmiller, Ted. Astronautics: A Historical Perspective of Mankind's Efforts to Conquer the Cosmos. Apogee Books. ISBN 9781894959667. Retrieved 10 January 2017.
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  49. ^ MacNiven 1995
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  51. ^ Fogg 2000
  52. ^ Christopher McKay and Robert Zubrin, "Do Indigenous Martian Bacteria have Precedence over Human Exploration?", pp. 177–182, in On to Mars: Colonizing a New World, Apogee Books Space Series, 2002, ISBN 1-896522-90-4
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  55. ^ Thompson 2001 p. 108

Notes

  • Averner, M. M. & MacElroy, R. D. (1976). On the Habitability of Mars: An Approach to Planetary Ecosynthesis. NASA SP-414.
  • Carr, Michael H. (2007). "Mars: Surface and interior". In Adams-McFadden, Lucy-Ann; Weissman, Paul Robert; Johnson, Torrence V. Encyclopedia of the solar system. Academic Press. pp. 315–330. ISBN 0-12-088589-1.
  • Dalrymple, G. Brent (2004). Ancient Earth, ancient skies: the age of Earth and its cosmic surroundings. Stanford University Press. ISBN 0-8047-4933-7
  • Faure, Gunter & Mensing, Teresa M. (2007). Introduction to planetary science: the geological perspective. Springer. ISBN 1-4020-5233-2.
  • Fogg, Martyn J. (1995). Terraforming: Engineering Planetary Environments. SAE International, Warrendale, PA. ISBN 1-56091-609-5.
  • Fogg, Martyn J. (1996). "A Planet Dweller's Dream". In Schmidt, Stanley; Zubrin, Robert. Islands in the Sky. New York: Wiley. pp. 143–67.
  • Fogg Martyn J. (2000). The Ethical Dimensions of Space Settlement (PDF format). Space Policy, 16, 205–211. Also presented (1999) at the 50th International Astronautical Congress, Amsterdam (IAA-99-IAA.7.1.07).
  • Fogg, Martyn J. (1998). "Terraforming Mars: A Review of Current Research" (PDF). Advances in Space Research. Committee on Space Research. 2 (3): 415–420. Bibcode:1998AdSpR..22..415F. doi:10.1016/S0273-1177(98)00166-5.
  • Forget, François; Costard, François & Lognonné, Philippe (2007). Planet Mars: Story of Another World. Springer. ISBN 0-387-48925-8.
  • Kargel, Jeffrey Stuart (2004). Mars: a warmer, wetter planet. Springer. ISBN 1-85233-568-8.
  • MacNiven, D. (1995). "Environmental Ethics and Planetary Engineering". Journal of the British Interplanetary Society. 48: 441–44.
  • Knoll, Andrew H. (2008). "Cyanobacteria and earth history". In Herrero, Antonia; Flores, Enrique. The cyanobacteria: molecular biology, genomics, and evolution. Horizon Scientific Press. pp. 1–20. ISBN 1-904455-15-8.
  • McKay Christopher P. & Haynes, Robert H. (1997). Implanting Life on Mars as a Long Term Goal for Mars Exploration, in The Case for Mars IV: Considerations for Sending Humans, ed. Thomas R. Meyer (San Diego, California: American Astronautical Society/Univelt), Pp. 209–15.
  • Read, Peter L.; Lewis, Stephen R. (2004). The Martian climate revisited: atmosphere and environment of a desert planet. Springer. ISBN 3-540-40743-X.
  • Sagan, Carl & Druyan, Ann (1997). Pale Blue Dot: A Vision of the Human Future in Space. Ballantine Books. ISBN 0-345-37659-5.
  • Schubert, Gerald ; Turcotte, Donald L.; Olson, Peter. (2001). Mantle convection in the Earth and planets. Cambridge University Press. ISBN 0-521-79836-1
  • Solar wind ripping chunks off Mars. (November 25, 2008) Cosmos Accessed 6/18/2009.
  • Taylor, Richard L. S. (1992) Paraterraforming – The worldhouse concept. Journal of the British Interplanetary Society, vol. 45, no. 8, pp. 341–352.ISSN 0007-084X
  • Thompson, J. M. T. (2001). Visions of the future: astronomy and Earth science. Cambridge University Press. ISBN 0-521-80537-6.

External links

Astrobiology (journal)

Astrobiology is a peer-reviewed scientific journal covering research on the origin, evolution, distribution and future of life across the universe. The journal's scope includes astrophysics, astropaleontology, bioastronomy, cosmochemistry, ecogenomics, exobiology, extremophiles, geomicrobiology, gravitational biology, life detection technology, meteoritics, origins of life, planetary geoscience, planetary protection, prebiotic chemistry, space exploration technology and terraforming.

Aurora (novel)

Aurora is a 2015 novel by American science fiction author Kim Stanley Robinson. The novel concerns a generation ship traveling to Tau Ceti in order to begin a human colony. The novel's primary narrating voice is the starship's artificial intelligence. The novel was well received by critics.

Christopher McKay

Christopher P. McKay is a planetary scientist at NASA Ames Research Center, studying planetary atmospheres, astrobiology, and terraforming. McKay majored in physics at Florida Atlantic University, where he also studied mechanical engineering, graduating in 1975, and received his PhD in astrogeophysics from the University of Colorado in 1982.

Colonization of Europa

Europa, the fourth-largest moon of Jupiter, is a subject in both science fiction and scientific speculation for future human colonization. Europa's geophysical features, including a possible subglacial water ocean, make it a possibility that human life could be sustained on or beneath the surface.

Colonization of Venus

The colonization of Venus has been a subject of many works of science fiction since before the dawn of spaceflight, and is still discussed from both a fictional and a scientific standpoint. However, with the discovery of Venus's extremely hostile surface environment, attention has largely shifted towards the colonization of the Moon and Mars instead, with proposals for Venus focused on colonies floating in the upper-middle atmosphere and on terraforming.

Desolation Road

Desolation Road is a 1988 science fiction novel written by Ian McDonald. It was McDonald's first published novel. The plot takes place on a far future Mars in a town that develops around an oasis in the terraformed Martian desert. McDonald published a sequel, Ares Express, in 2001.

Earth analog

An Earth analog (also referred to as an Earth analogue, Earth twin, or Earth-like planet, though this latter term may refer to any terrestrial planet) is a planet or moon with environmental conditions similar to those found on Earth.

The possibility is of particular interest to astrobiologists and astronomers under reasoning that the more similar a planet is to Earth, the more likely it is to be capable of sustaining complex extraterrestrial life. As such, it has long been speculated and the subject expressed in science, philosophy, science fiction and popular culture. Advocates of space colonization have long sought an Earth analog as a "second home", while advocates for space and survival would regard such a planet as a potential "new home" for humankind.

Before the scientific search for and study of extrasolar planets, the possibility was argued through philosophy and science fiction. The mediocrity principle suggests that planets like Earth should be common in the universe, while the Rare Earth hypothesis suggests that they are extremely rare. The thousands of exoplanetary star systems discovered so far are profoundly different from our solar system, supporting the Rare Earth hypothesis.

Philosophers have pointed out that the size of the universe is such that a near-identical planet must exist somewhere. In the far future, technology may be used by humans to artificially produce an Earth analog by terraforming. The multiverse theory suggests that an Earth analog could exist in another universe or even be another version of the Earth itself in a parallel universe.

On November 4, 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarf stars within the Milky Way galaxy. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away.Scientific findings since the 1990s have greatly influenced the scope of the fields of astrobiology, models of planetary habitability and the search for extraterrestrial intelligence (SETI). NASA and the SETI Institute have proposed categorising the increasing number of planets found using a measure called the Earth Similarity Index (ESI) based on mass, radius and temperature. According to this measure, as of 23 July 2015, the confirmed planet currently thought to be most similar to Earth on mass, radius and temperature is Kepler-438b. Scientists estimate that there may be billions of Earth-size planets within the Milky Way galaxy alone.

Ethics of terraforming

The ethics of terraforming has constituted a philosophical debate within biology, ecology, and environmental ethics as to whether terraforming other worlds is an ethical endeavor.

Mars trilogy

The Mars trilogy is a series of award-winning science fiction novels by Kim Stanley Robinson that chronicles the settlement and terraforming of the planet Mars through the personal and detailed viewpoints of a wide variety of characters spanning almost two centuries. Ultimately more utopian than dystopian, the story focuses on egalitarian, sociological, and scientific advances made on Mars, while Earth suffers from overpopulation and ecological disaster.

The three novels are Red Mars (1992), Green Mars (1993), and Blue Mars (1996). The Martians (1999) is a collection of short stories set in the same fictional universe. The main trilogy won a number of prestigious awards. Icehenge (1984), Robinson's first novel about Mars, is not set in this universe but deals with similar themes and plot elements. The trilogy shares some similarities with Robinson's more recent novel 2312 (2012), for instance, the terraforming of Mars and the extreme longevity of the characters in both novels.

Martyn J. Fogg

Martyn J. Fogg (born 3 July 1960) is a British physicist and geologist, an expert on terraforming.

Planetary engineering

Planetary engineering is the application of technology for the purpose of influencing the global environments of a planet. Its objectives usually involve increasing the habitability of other worlds or mitigating decreases in habitability to Earth.

Perhaps the best-known type of planetary engineering is terraforming, by which a planet's surface conditions are altered to be more like those of Earth. Planetary engineering is largely the realm of science fiction at present, although recent climate change on Earth shows that human technology can cause change on a global scale.

Robert Zubrin

Robert Zubrin (; born April 9, 1952) is an American aerospace engineer and author, best known for his advocacy of human exploration of Mars. He and his colleague at Martin Marietta, David Baker, were the driving force behind Mars Direct, a proposal intended to produce significant reductions in the cost and complexity of such a mission. The key idea was to use the Martian atmosphere to produce oxygen, water, and rocket propellant for the surface stay and return journey. A modified version of the plan was subsequently adopted by NASA as their "design reference mission". He questions the delay and cost-to-benefit ratio of first establishing a base or outpost on an asteroid or another Project Apollo-like return to the Moon, as neither would be able to provide all of its own oxygen, water, or energy; these resources are producible on Mars, and he expects people would be there thereafter.Disappointed with the lack of interest from government in Mars exploration and after the success of his book The Case for Mars, as well as leadership experience at the National Space Society, Zubrin established the Mars Society in 1998. This is an international organization advocating a manned Mars mission as a goal, by private funding if possible.

Terra Formars (film)

Terra Formars (Japanese: テラフォーマーズ, Hepburn: Tera Fōmāzu) is a 2016 Japanese science fiction film directed by Takashi Miike and based on the manga series of the same name by Yū Sasuga & Kenichi Tachibana. It was released in Japan on Friday, April 29, 2016.

Terraforming Mars (board game)

Terraforming Mars is a board game for 1 to 5 players designed by Jacob Fryxelius and published by FryxGames in 2016, and thereafter by 12 others, including Stronghold Games.

In Terraforming Mars players take the role of corporations working together to terraform the planet by raising the temperature and creating oxygen, water, and plant and animal life. Players compete to earn the most victory points, which are measured by their contribution to terraforming, as well as building human infrastructure.

Players accomplish these goals by collecting income and resources which allow them to play different cards, which represent either buildings or events, which then increase their income or resources or directly contribute to terraforming the planet or building infrastructure.

The game has been well received by fans and critics, winning or being nominated for multiple awards and accolades.

Terraforming in popular culture

Terraforming is well represented in popular culture, usually in the form of science fiction. While many stories involving interstellar travel feature planets already suited to habitation by humans and supporting their own indigenous life, some authors prefer to address the unlikeliness of such a concept by instead detailing the means by which humans have converted inhospitable worlds to ones capable of supporting life through artificial means.

Author Jack Williamson is credited with inventing and popularizing the term "terraform". In July 1942, under the pseudonym Will Stewart, Williamson published a science fiction novella entitled "Collision Orbit" in Astounding Science-Fiction magazine. The series was later published as two novels, Seetee Shock (1949) and Seetee Ship (1951). American geographer Richard Cathcart successfully lobbied for formal recognition of the verb "to terraform", and it was first included in the fourth edition of the Shorter Oxford English Dictionary in 1993.

Terraforming of Mars

Terraforming of Mars is a hypothetical process of planetary engineering by which the surface and climate of Mars would be deliberately changed to make large areas of the environment hospitable to humans, thus making the colonization of Mars safer and sustainable.

There are a few proposed terraforming concepts, some of which present prohibitive economic and natural resource costs. As of 2019 it is not feasible, using existing technology, to terraform Mars. Any climate change induced in the near term is proposed to be driven by greenhouse warming produced by an increase in atmospheric CO2 and a consequent increase in atmospheric water vapor, but Mars does not retain enough carbon dioxide that could practically be put back into the atmosphere to warm it.

Terraforming of Venus

The terraforming of Venus is the hypothetical process of engineering the global environment of the planet Venus in such a way as to make it suitable for human habitation. Terraforming Venus was first scholarly proposed by the astronomer Carl Sagan in 1961, although fictional treatments, such as The Big Rain of The Psychotechnic League by novelist Poul Anderson, preceded it. Adjustments to the existing environment of Venus to support human life would require at least three major changes to the planet's atmosphere:

Reducing Venus' surface temperature of 462 °C (735 K; 864 °F)

eliminating most of the planet's dense 9.2 MPa (91 atm) carbon dioxide and sulfur dioxide atmosphere via removal or conversion to some other form

the addition of breathable oxygen to the atmosphere.These three changes are closely interrelated, because Venus' extreme temperature is due to the high pressure of its dense atmosphere, and the greenhouse effect.

The Case for Mars

The Case for Mars: The Plan to Settle the Red Planet and Why We Must is a nonfiction science book by Robert Zubrin, first published in 1996, and revised and updated in 2011.

The book details Zubrin's Mars Direct plan to make the first human landing on Mars. The plan focuses on keeping costs down by making use of automated systems and available materials on Mars to manufacture the return journey's fuel in situ. The book also reveals possible Mars colony designs and weighs the prospects for a colony's material self-sufficiency and for the terraforming of Mars.

The Mammoth Trilogy

The Mammoth Trilogy is a series of books by hard science fiction author Stephen Baxter. The books in it were published between 1999 and 2001. It contains the novels Silverhair, Longtusk and Icebones.

An omnibus volume containing all three novels was released in 2004, with the title Behemoth.

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