Terraforming

From Wikipedia, the free encyclopedia

Artist's conception of a terraformed Mars in four stages of development. (credit: Daein Ballard)

Terraforming (literally, "Earth-shaping") is the theoretical process of modifying a planet, moon, or other body to a more habitable atmosphere, temperature, or ecology. It is a type of planetary engineering. The term is sometimes used broadly as a synonym for planetary engineering in general. The concepts of terraforming are rooted both in science fiction and actual science. The term was probably coined by Jack Williamson in a science-fiction story published in 1942 in Astounding Science Fiction,^[1] but the actual concept pre-dates this work. Olaf Stapledon's Last and First Men (1930)^[2] provides an example in fiction in which Venus is modified after a long and destructive war with the original inhabitants, who naturally object to the process.

Since space exploration is in its infancy, a good deal of terraforming remains speculative. Based on what we know of our own world it seems possible to affect the environment in a deliberate way in order to change it; however the feasibility of creating an unconstrained planetary biosphere that mimics Earth on another planet has yet to be verified. Mars is considered by many to be the most likely candidate for terraformation. Much study has gone into the possibility of heating the planet and altering its atmosphere, and NASA has even hosted debates on the subject. However, a multitude of obstacles stand between the present and an active terraforming effort on Mars or any other world. 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.

[edit] History of scholarly study

Carl Sagan, an astronomer and popularizer of science, proposed the planetary engineering of Venus in a 1961 article published in the journal Science entitled, "The Planet Venus."^[3] Sagan imagined seeding the atmosphere of Venus with algae, which would remove carbon dioxide and reduce the greenhouse effect until surface temperatures dropped to "comfortable" levels. 3 billion years ago, the Earth had a carbon dioxide atmosphere. Blue-green algae and water evaporation changed the earth's atmosphere into oxygen and hydrogen gas. Later discoveries about the conditions on Venus made this particular approach impossible since Venus has too much atmosphere to process and sequester. Even if atmospheric algae could thrive in the hostile and arid environment of Venus's upper atmosphere, any carbon that was fixed in organic form would be liberated as carbon dioxide again as soon as it fell into the hot lower regions.

Sagan also visualized making Mars habitable for human life in "Planetary Engineering on Mars," a 1973 article published in the journal Icarus.^[4] Three years later, NASA officially addressed the issue of planetary engineering in a study, but used the term planetary ecosynthesis instead.^[5] The study concluded that there was no known limitation in the ability to alter Mars to support life and be made into a habitable planet. That same year, in 1976, one of the researchers, Joel Levine, organized the first conference session on terraforming, which at the time was called "Planetary Modeling."

In March 1979, NASA engineer and author James Oberg organized the "First Terraforming Colloquium," a special session on terraforming held at the Lunar and Planetary Science Conference in Houston. Oberg popularized the terraforming concepts discussed at the colloquium to the general public in his 1981 book, New Earths.^[6] It wasn't until 1982 that the word terraforming was 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 books to describe a novel method of warming Mars, where chlorofluorocarbons are added to the atmosphere. Motivated by Lovelock's book, biophysicist Robert Haynes worked behind the scenes to promote terraforming, and contributed the word ecopoiesis to its lexicon.

Beginning in 1985, Martyn J. Fogg began 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 1991, and in 1995 published the book Terraforming: Engineering Planetary Environments.^[9] Fogg also maintains an active website called The Terraforming Information Pages.

Fogg used the following definitions for different aspects related to terraforming:

• Planetary Engineering: the application of technology for the purpose of influencing the global properties of a planet.
• Geoengineering: planetary engineering applied specifically to the 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 extra-terrestrial planetary environment to support life. The ultimate in terraforming would be to create an uncontained planetary biosphere emulating all the functions of the biosphere of the Earth, one that would be fully habitable for human beings.
• Astrophysical Engineering: taken to represent proposed activities, relating to future habitation, that are envisaged to occur on a scale greater than that of "conventional" planetary engineering.

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

• Habitable Planet (HP): A world with an environment sufficiently similar to the 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 designates Mars as having been a biocompatible planet in its youth, but not being in any of these three categories in its present state, since it could only be terraformed with relatively greater difficulty. Mars Society founder Robert Zubrin produced a plan for a Mars return mission called Mars Direct that would set up a permanent human presence on Mars and steer efforts towards eventual terraformation.^[10]

The principal reason given to pursue terraforming is the creation of an ecology to support worlds suitable for habitation by humans. However, some researchers believe that space habitats will provide a more economical means for supporting space colonization. If research in nanotechnology and other advanced chemical processes continues apace, it may become feasible to terraform planets in centuries rather than millennia. On the other hand, it may become reasonable to modify humans so that they don't require an oxygen/nitrogen atmosphere in a 1 g gravity field to live comfortably. That would then reduce the need to terraform worlds, or at least the degree to which other worlds' environments would need to be altered.

[edit] Requirements for sustaining terrestrial life

Main article: Planetary habitability

The only 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 an astronomical body is able to support life. Of particular interest is the set of factors that has sustained complex, multicellular animals and not merely unicellular organisms on this planet. Research and theory in this regard is a component of planetary science and the emerging discipline of astrobiology. Not only are there planetary requirements, there are theories as to the type and age of the star. ^{[citation needed]}

[edit] Theoretical methods of terraforming

Artist's conception of a terraformed Mars. This realistic portrayal is approximately centered on the prime meridian and 30 degrees north latitude, with the north polar cap at upper left, and a hypothesized ocean with a sea level at approximately two kilometers below average surface elevation. The ocean submerges what are now Vastitas Borealis, Acidalia Planitia, Chryse Planitia, and Xanthe Terra; the visible landmasses are Tempe Terra at left, Aonia Terra at bottom, Terra Meridiani at lower right, and Arabia Terra at upper right. Rivers that feed the ocean at lower right occupy what are now Valles Marineris and Ares Vallis, while the large lake at lower right occupies what is now Aram Chaos. (credit: Mathew Crisp).

Photorealistic conception of a terraformed Mars. In the middle showing the Mariner Bay which was once the Mariner Valley and way up in the north part of the arctic Acidalia Planitia Sea.

[edit] Building the atmosphere

Since ammonia is a powerful greenhouse gas, and it is possible that nature has stockpiled large amounts of it in frozen form on asteroidal sized objects orbiting in the outer solar system, it may be possible to move these and send them into a planet's atmosphere. Since ammonia is NH₃ it would also take care of the problem involved in needing a buffer gas in the atmosphere. Impacting a comet onto the surface of the planet might cause destruction to the point of being counter-productive. Aerobraking, if an option, would allow a comet's frozen mass to outgas and become part of the atmosphere through which it would travel. It may be better to impact several smaller asteroids into the planet, both to build up the planet mass and to add to the atmosphere. Keeping these smaller impacts on their own will eventually build up the temperature as well as mass to both the planet and its atmosphere. The need for a buffer gas is a challenge that will face any potential atmosphere builders. On Earth, nitrogen is the primary atmospheric component making up 77% of the atmosphere. Some planets would require a similar buffer gas component although not necessarily as much. Still, obtaining significant quantities of nitrogen, argon or some other non-volatile gas could prove difficult.

Hydrogen importation could also be done for atmospheric and hydrospheric engineering. Depending on the level of carbon dioxide in the atmosphere, importation and reaction of hydrogen would produce heat, water and graphite via the Bosch reaction. Adding water and heat to the environment will be key to making the dry, cold world suitable for Earth life. Alternatively, reacting hydrogen with the carbon dioxide atmosphere via the Sabatier reaction would yield methane and water. The methane could be vented into the atmosphere where it would act to compound the greenhouse effect. Presumably, hydrogen could be obtained in bulk from the gas giants or refined from hydrogen-rich compounds in other outer solar system objects, though the energy required to transport large quantities would be great. Simply thickening the planet's atmosphere will not make it habitable for Earth life unless it contains the proper mix of gases. Achieving a suitable mixture of buffer gas, oxygen, carbon dioxide, water vapor and trace gases will entail either direct processing of the atmosphere or altering it by means of plant life and other organisms. Genetic engineering would allow such organisms to process the atmosphere more efficiently and survive in the otherwise hostile environment.^{[citation needed]}

[edit] Converting atmosphere

A planet's atmosphere could potentially be converted into some other form in situ by reacting it with externally supplied elements. For example, bombardment of Venus with refined magnesium and calcium metal from Mercury or some other source, could sequester carbon dioxide in the form of calcium and magnesium carbonates. About 8×10²⁰ kg of calcium or 5×10²⁰ kg of magnesium would be required, which would entail a great deal of mining and mineral refining to obtain.^[11]

Bombardment with hydrogen, possibly from some outer solar system source and reacting with carbon dioxide could produce elemental carbon (graphite) and water by the Bosch reaction. Considerable amounts of hydrogen would be required to convert a planet's entire atmosphere.^{[citation needed]} The amount of water produced would amount to around 10% of the water found on Earth.

A solar shade or equivalent would also be necessary, as water vapor is itself a greenhouse gas. Oceans would decrease the planet's albedo and allow more incoming solar radiation to be absorbed before being reflected back into space, resulting in further warming.^{[citation needed]} It would also be important to take into account water's capacity for absorbing CO₂ and O₂, and how much gas an ocean would hold. In addition to this, habitable planets need a significant percentage of nitrogen in their new atmospheres, as nitrogen is an important component of proteins in all living things and acts as a buffer against chemical reactions by oxygen. Over 3.2 bar of nitrogen is present in Venus's atmosphere, also nitrogen is present in the outer solar system in the form of NH₃ on comets, the mostly nitrogen atmosphere of Titan, and nitrogen ices on the surfaces of Triton and Pluto, and thus could be an important source of this gas.

A method proposed in 1961 by Carl Sagan involves the use of genetically engineered bacteria to fix carbon into organic forms.^[3] Although this method is still commonly proposed in discussions of Venus terraforming, later discoveries showed it would not be successful; organic carbon would be liberated into carbon dioxide again by the hot surface environment. However, using the Bosch reaction to create more water would pave the way for microbes to survive in the atmosphere, which would lower the amount of hydrogen needed from imports.^{[citation needed]}

[edit] Removing atmosphere

Removal of atmosphere could be attempted by a variety of methods, possibly in combination. Directly lifting atmospheric gas into space would likely prove very difficult. For example, Venus has sufficiently high escape velocity to make blasting it away with asteroid impacts impractical. Pollack and Sagan calculated in 1993^{[citation needed]} that an impactor of 700 km diameter striking Venus at greater than 20 km/s, would eject all the atmosphere above the horizon as seen from the point of impact, but since this is less than a thousandth of the total atmosphere and there would be diminishing returns as the atmosphere's density decreased a very great number of such giant impactors would be required. Smaller objects would not work either; even more would be necessary. The violence of the bombardment could well result in significant outgassing that replaces removed atmosphere. Furthermore, most of the ejected atmosphere would go into solar orbit near Venus, eventually to fall right back onto Venus again.

Removal of atmospheric gas in a more controlled manner could also prove difficult. A planet like Venus's extremely slow rotation means that space elevators would be impossible to construct, and the very atmosphere to be removed makes mass drivers useless for removing payloads from the planet's surface. Possible workarounds include placing mass drivers on high-altitude balloons or balloon-supported towers extending above the bulk of the atmosphere, using space fountains, or rotovators. Such processes would take a great deal of technical sophistication and time, however, and may not be economically feasible without the use of extensive automation.^{[citation needed]}

[edit] Paraterraforming

Also known as the "worldhouse" concept, or domes in smaller versions, paraterraforming involves the construction of a habitable enclosure on a planet which eventually grows to encompass most of the planet's usable area. The enclosure would consist of a transparent roof held one or more kilometres above the surface, pressurized with a breathable atmosphere, and anchored with tension towers and cables at regular intervals. Proponents claim worldhouses can be constructed with technology known since the 1960s.

Paraterraforming has several advantages over the traditional approach to terraforming. For example, it provides an immediate payback to investors; the worldhouse starts out small in area (a domed city for example), but those areas provide habitable space from the start. The paraterraforming approach also allows for a modular approach that can be tailored to the needs of the planet's population, growing only as fast and only in those areas where it is required. Finally, paraterraforming greatly reduces the amount of atmosphere that one would need to add to planets like Mars in order to provide Earthlike atmospheric pressures. By using a solid envelope in this manner, even bodies which would otherwise be unable to retain an atmosphere at all (such as asteroids) could be given a habitable environment. The environment under an artificial worldhouse roof would also likely be more amenable to artificial manipulation.

It has the disadvantage of requiring a great deal of construction and maintenance activity, the cost of which could be ameliorated to some degree through the use of automated manufacturing and repair mechanisms. A worldhouse could also be more susceptible to catastrophic failure in the event of a major breach, though this risk can likely be reduced by compartmentalization and other active safety precautions. Meteor strikes are a particular concern in the absence of any external atmosphere in which they would burn up before reaching the surface.

[edit] Cloud-top colonization

Geoffrey A. Landis proposes colonizing the cloud-tops of planets like Venus.^[12] Initially, the image of floating cities may seem fanciful, but Landis' proposal points out that a Terran breathable air mixture (21:79 Oxygen-Nitrogen) is a lifting gas in the dense Venusian atmosphere. In effect, a gasbag full of human-breathable air would sustain itself and extra weight (such as a colony) in midair. At an altitude of 50 kilometers above Venusian surface, the environment is the most Earthlike in the solar system - a pressure of approximately 1 bar and temperatures in the 0-50 Celsius range. Because there is not a significant pressure differential between the inside and the outside of the breathable-air balloon, any rips or tears would not result in an explosive decompression, but rather would only diffuse at normal atmospheric mixing rates, giving time to repair any such defects.

Such colonies could be constructed at any rate desired, allowing a dynamic approach instead of needing any 'fell swoop' solutions. They could be used to gradually transform the atmosphere, with their impact directly related to the number of colonies in the atmosphere. As the constructed colonies increased, more solar panels could be used to absorb insolation and thus cool Venus; they could also be used to grow plant matter that would reduce the amount of carbon dioxide in the air. In the beginning, any impact would be insignificant, but as the number of colonies grew, they could transform Venus more and more rapidly.

[edit] Adding heat

Mirrors made of extremely thin aluminized PET film could be placed in orbit of a planet to increase the total insolation it receives. ^[13] This would increase the planet's temperature directly, and also vaporize water and carbon dioxide to increase the planet's greenhouse effect. While producing halocarbons would contribute to adding mass to the atmosphere, their primary function would be to trap incoming solar radiation. Halocarbons (such as CFCs and PFCs) are powerful greenhouse gases, and are stable for lengthy periods of time in atmospheres. They could be produced by genetically engineered aerobic bacteria or by mechanical contraptions scattered across the planet's surface.

Changing the albedo of the planetary surface would also make more efficient use of incoming sunlight. Altering the color of the surface with dark dust, soot, dark microbial life forms or lichens would transfer a larger amount of incoming solar radiation to the surface as heat before it is reflected off into space again. Using life forms is particularly attractive since they could propagate themselves.

Nuclear bombardment of the crust and the polar caps has been suggested as a quick-and-dirty way of heating up the planet.^{[citation needed]} If detonated on polar regions, the intense heat would melt vast quantities of water and frozen carbon dioxide. The gases produced would thicken the atmosphere and contribute to the greenhouse effect. Additionally, the dust kicked up by a nuclear explosion would fall on the ice and decrease its albedo thus allowing it to melt faster under the sun’s rays. Detonation of nuclear weapons under the surface would heat the crust and help speed outgassing of trapped carbon dioxide. While using nuclear devices is attractive in the sense that it makes use of aging and dangerous Earth weaponry and adds quick and cheap heat to the planet, it carries the ugly connotations of mass destruction to the native environment and potential harmful effects of nuclear fallout.

Another possibility to heat a planet's surface would be to place a microwave array, powered by solar cells, nuclear reactor, or a combination of the two, into synchronous orbit.^{[citation needed]} Microwaves of approximately 2.45 GHz are used in microwave ovens to cause vibrations in water molecules and produce heat. If microwaves of this frequency with sufficient amplitude were focused onto the surface it would heat the ice crystals trapped in the soil. A long enough exposure to the microwaves would release the water into the atmosphere and gradually heat the surface of the planet. Several such arrays could be placed in orbit and designed to gradually sweep the beam across vast areas. One drastic proposal for adding some heat to Mars, for example, is to brake the inner moon, Phobos, so that it crashes into the surface.^{[citation needed]} Apart from the comparatively little heat generated by this, it removes an important danger for future settlements: A thickening atmosphere would slow down Phobos so much that it would crash land within a few hundred years anyway. Thinking far into the future, some scientists point out that the Sun will eventually grow too hot for Earth to sustain life, even before it becomes a red giant star. All main sequence stars brighten slowly throughout their lifetimes. As a result, a planet like Mars will warm up on its own, making terraforming easier.

[edit] Removing heat

Solar shades placed in the Sun-Venus L₁ point or in a more closely-orbiting ring could be used to reduce the total insolation received by a planet like Venus, cooling the planet somewhat. This does not directly deal with the immense atmospheric density of Venus-like planets, but could make it easier to do so by other methods. They could also serve double duty as solar power generators. Construction of a suitably large solar shade is a potentially daunting task. The sheer size of such a structure would necessitate construction in space. There would also be the difficulty of balancing a thin-film shade at the Sun-Venus L₁ point with the incoming radiation pressure which would tend to turn the shade into a huge solar sail. If the shade is left at the L1 point, the pressure would add too much force to the sunward side and necessitate moving the shade even closer to the sun than the L1 point. The size of the shade would be twice the diameter of Venus itself if at the L1 point. But modifications do exist that can reduce this size and the location of the shade. If the shade's panels are not perpendicular to the sun's rays but instead at an angle of 30 degrees and then the light is reflected to the next panel outward which will be +/- 1 degree off the 30 degrees which then reflects the light back just 4 degrees from striking Venus. The photon pressure from this arrangement is very small. Another element necessary to bring the shade closer to Venus and reduce its size is to use polar orbiting, sun-synchronous mirrors that reflects light from the non sunward side of Venus. Photon pressure would push the support mirrors to an angle of 30 degrees away from the sunward side.^[9] Other proposed cooling solutions involve comets,^{[citation needed]} or creating artificial rings. A comet at the Sun-Venus L₁ point could produce a coma which could provide at least temporary shade for the planet, possibly allowing enough time for atmospheric processing to be done. Keeping a continuously decaying comet in a stable position could prove to be a difficult feat. Rings created by putting debris in orbit would provide some shade but to a lesser extent. The inclination of the rings would also need to be such that they present a significant amount of surface area to the Sun. Space-based solar shade techniques are largely speculative due to the fact that they are beyond our current technological grasp. The vast sizes require material strengths and construction methods that have not even reached their infancy.

Cooling could be sustained by placing reflectors in the atmosphere or on the surface. Reflective balloons floating in the upper atmosphere could create shade. The number and/or size of the balloons would necessarily be great. Increasing the planet's albedo by deploying light color or reflective material on the surface could help keep the atmosphere cool. The amount would be large and would have to be put in place after the atmosphere had been modified already since some planets surfaces are like Venus and are currently completely shrouded by clouds. The advantage of atmospheric and surface cooling solutions is that they take advantage of existing technology.^{[citation needed]}

To keep a strong and stable atmosphere on Mars, greenhouse gases would need to be used. Though a hotly debated topic today, greenhouse gases would greatly increase heat on Mars, making it a more hospitable environment for humans to live in.

[edit] Building a shield against radiation

Another significant, and probably the most overlooked, aspect of terraforming Mars would be the lack of a magnetosphere. The magnetosphere deflects most of the hard particulate radiation from the solar wind. Without some form of radiation protection anyone on Mars would have prolonged exposure to an unhealthy amount of radiation every time a serious solar eruption occurred. The lack of a magnetosphere is thought to have caused the Martian atmosphere to become as thin as it is in the first place by allowing solar wind to heat the top layers of the atmosphere, enabling atmospheric particles to reach escape velocity and leave Mars (essentially "blowing" the atmosphere away, though the term would be inaccurate in this case). Indeed, this effect has even been detected by Mars-orbiting probes. Venus, however, shows that the lack of a magnetosphere does not preclude an atmosphere. A thick atmosphere will also provide radiation protection for the surface, as it does at Earth's polar regions where aurorae form, so in the short term the lack of a magnetosphere would not seriously impact the habitability of a terraformed Mars. ^{[citation needed]}

On a longer timescale, and with the technology of the future (in perhaps 25-50 years), an artificial magnetosphere seems possible: If the energy of several large fusion-power-stations is used to power large superconducting magnets - the field should be strong enough to protect at least local settlements. ^{[citation needed]} However, recent scientific evidence suggest that just a thick enough atmosphere like Earth's is enough to create a magnetic shielding in an absence of a magnetosphere. In the past, Earth regularly had periods where the magnetosphere changed direction and collapsed for some time. Scientists believe that in the ionosphere, a magnetic shielding was created almost instantly after the magnetosphere collapsed.^[14] This principle applies to Venus as well and would also be the case in every other planet or moon with a large enough atmosphere. Venus also lacks a magnetic field. It is thought that this may have contributed greatly to its current uninhabitable state, as the upper atmosphere is exposed to direct erosion by solar wind and has lost most of its original hydrogen to space. However, this process is extremely slow, and so is unlikely to be significant on the timescale of any civilization capable of terraforming the planet in the first place.

[edit] Planet rotation speed

Venus's extremely slow rotation rate would result in extremely long days and nights, which could prove difficult for most Earth life to adapt to. Speeding up Venus's rotation would require many orders of magnitude greater amounts of energy than removing its atmosphere would, and so is likely to be infeasible (at least by any current technology). Instead, a system of orbiting solar mirrors might be used to provide sunlight to the night side of Venus. Alternately, instead of requiring that Venus support life identical to Earth's, Earth life could instead be modified to adapt to the long Venusian day and night. However, Venusian cloud-top colonies could be given the ability to have a shorter day, even down to 24 hours, by using anti-corrosive wind sails to propel them around the planet instead of depending on the planet's rotation or appendages.^{[citation needed]}

[edit] Further stages of terraforming

Main article: Ecopoiesis

Once conditions become more suitable to life from Earth, the importation of microbial life could begin.^[9] 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 and human life.

[edit] Prospective planets

[edit] Mars

Artist's conception of a terraformed Mars in three stages of development. (credit: Michael Carroll)

Main article: Martian terraforming

See also: Colonization of Mars

There is some scientific debate over whether it would even be possible to terraform Mars, or how stable its climate would be once terraformed. It is possible that over geological timescales - tens or hundreds of millions of years—Mars could lose its water and atmosphere again, possibly to the same processes that reduced it to its current state. Indeed, it is thought that Mars once did have a relatively Earthlike environment early in its history, with a thicker atmosphere and abundant water that was lost over the course of hundreds of millions of years. The exact mechanism of this loss is still unclear, though several mechanisms have been proposed. The lack of a magnetosphere surrounding Mars may have allowed the solar wind to erode the atmosphere, the relatively low gravity of Mars helping to accelerate the loss of lighter gases to space. The lack of plate tectonics on Mars is another possibility, preventing the recycling of gases locked up in sediments back into the atmosphere. The lack of magnetic field and geologic activity may both be a result of Mars's smaller size allowing its interior to cool more quickly than Earth's, though the details of such processes are still unrealized. However, none of these processes are likely to be significant over the typical lifespan of most animal species, or even on the timescale of human civilization, and the slow loss of atmosphere could possibly be counteracted with ongoing low-level artificial terraforming activities. Terraforming Mars would entail two major interlaced changes: building the atmosphere and heating it. Since a thicker atmosphere of carbon dioxide and/or some other greenhouse gases would trap incoming solar radiation and the raised temperature would put the greenhouse gases into the atmosphere the two processes would augment one another. ^{[citation needed]}

[edit] Venus

Artist's conception of a terraformed Venus. (credit: Daein Ballard)

Main article: Venusian terraforming

See also: Colonization of Venus

Terraforming Venus requires two major changes; removing most of the planet's dense 9 MPa carbon dioxide atmosphere and reducing the planet's 500 °C (770 K) surface temperature. These goals are closely interrelated, since Venus's extreme temperature is due to the greenhouse effect caused by its dense atmosphere. Sequestering the atmospheric carbon would likely solve the temperature problem as well. Venus, unlike Mars, is tectonically active, and could therefore function as a biosphericly viable copy of our Earth.

It may be possible to cool Venus down enough by mining aluminum from the Moon and shooting it into orbit around Venus by magnetic rail guns from the Moon. The aluminum dust would reflect sun light and cool down Venus. The aluminum dust should be timed to be released at once from orbiting containers. The dust would not remain in orbit for long so timing of a total comprehensive plan would be required. Comet impacts perhaps and planting of life at the North and South pole of Venus may work. If temperatures dropped and water was present it could help store the CO₂ as calcium carbonate. ^{[citation needed]}

It may be possible to use magnetic fields to aim solar flares at Venus. The ionized hydrogen gas may react with CO₂ forming methane and water. High altitude water ice crystals would reflect large amounts of heat, cooling Venus down.

[edit] Europa (moon)

Europa, a moon of Jupiter, is a potential prospect for terraforming. One of the advantages to Europa is the presence of liquid water which could be extremely helpful for the introduction of complex life.^[15] The difficulties are numerous; Europa is in the middle of a huge radiation belt around Jupiter, and a human would die within 10 minutes on the surface. This would require the building of huge radiation deflectors, which is currently impractical. Additionally, this satellite is covered in ice and would have to be heated, and there would need to be a supply of oxygen.^[16]

[edit] Other planets and solar system entities

Artist's conception of what the Moon might look like terraformed. As seen from Earth (credit: Daein Ballard)

See also: Colonization of the Moon, Colonization of Mercury, Colonization of the outer solar system, and Colonization of Ceres

Other possible candidates for terraformation include Titan, Mercury, Ganymede, Io, Callisto, Earth's Moon, and even the dwarf planet Ceres. Most, however, have too little mass to hold an atmosphere (although it is possible, but not certain, that an atmosphere could remain for tens of thousands of years, plenty of time on human timescales). In addition, aside from the Moon, most of these worlds are so far from the Sun that adding sufficient heat would be much more difficult than even Mars would be.

[edit] Ethical issues

Main article: Ethics of terraforming

There is a philosophical debate within biology and ecology as to whether terraforming other worlds is an ethical endeavor. On the pro-terraforming side of the argument, there are those like Robert Zubrin, Martyn J. Fogg, and Richard L. S. Taylor 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.^[17][18] 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 Terran life to become extinct. Some more cautious thinkers believe terraforming would be an unethical interference in nature, and that given humanity's past treatment of the 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, while we should not try to reshape the planet to our own use, we should engineer the planet's environment to artificially nurture the alien life and help it thrive and coevolve.^[19]

[edit] Economic issues

The cost of such projects as planetary terraforming would be gigantic, and the infrastructure of such an enterprise would have to be built from scratch. Such technology is not even practically possible, let alone financially possible at the moment and people like John Hickman point out that almost none of the current schemes for terraforming incorporate economic strategies, and most of their models and expectations are highly optimistic.^[20] Advocates of space colonization have argued that the same financial investment required to terraform Mars or Venus could produce a larger area of "land" if used to build space habitats instead. They argue that a civilization that knows how to live in space can survive anywhere in the solar system, whereas terraforming Mars will only help us to live in one place. ^{[citation needed]}

[edit] Political issues

Further information: Outer Space Treaty

There are many potential political issues arising from terraforming a planet, such as who gets to own the extra terrestrial land on the new planet, with contenders being national governments, trans-national organizations like the United Nations, Corporations or individual settlers themselves. Such settlements may become part of national disputes as countries try to make parts of other planets part of their own national territory. Rivalries between nations continue to be a primary motivation for shaping Space projects.^[21]

[edit] Popular culture

Main article: Terraforming in popular culture

Terraforming is a common concept in science fiction, ranging from television, movies, and video games. The concept of changing a planet for habitation actually precedes the concept of terraforming, with H. G. Wells alluding to xeno-terraforming, where aliens in his story The War of the Worlds change Earth for their own benefit. Also, Olaf Stapledon's Last and First Men (1930) provides the first example in fiction in which Venus is modified, after a long and destructive war with the original inhabitants, who naturally object to the process.

Terraforming has also been explored on television and in feature films, most prominently and famously in the Star Trek universe, in which, during the 22nd century, humanity has started terraforming Mars. In the series, part of this process involved diverting comets so that they would strike Mars in predetermined places, helping release water and oxygen into the atmosphere, and by 2154 the process had developed far enough along that pressure suits were no longer required - just oxygen masks to help compensate for the still thin atmosphere and cold weather garments were all that was needed by then. A century later the process had been completed. In the Star Trek movie The Wrath of Khan, Khan, the former dictator over most of Asia during the Eugenics Wars of the late 1990's, escapes exile from a desolate planet and steals the "Genesis Device", an energy matrix developed to quickly terraform barren planets, such as Mars, and wields it as a weapon, threatening to use it against already populated planets in order to conquer the galaxy. Eventually, it is used on Regula One, a planetoid, creating the Genesis Planet.

In Joss Whedon's short-lived hit television series Firefly, and its feature film sequel Serenity, giant "terraformers" (ships or factories designed to generate atmosphere and perform other functions of terraforming) were used to transform the ecosystems of hundreds of planets and moons in a new solar system into human-livable environments. This allowed the human race to escape from a resource-exhausted Earth and continue to grow into the fictional universe that both the series and the movie were set in.

In the television show Threshold, the aliens appear to be terraforming the Earth.

Terraforming appears on the online game, OGame, but are mostly primarily used to regain fields of land, which are used to construct more mines and buildings. In the Real Time Strategy game, Hegemonia: Legions of Iron, you can research the technology to terraform a planet, and then do so after it has been colonized. Terraforming can be done in the PC game Master of Orion II Battle at Antares. Terraforming has a major role in the plot of the upcoming Xbox 360 game, Lost Planet.

Terraforming shows up in Galactic Civilizations two as a research upgrade, allowing yellow squares to be utilized.

It is shown in the movie Aliens. An atmospheric factory is utilized to withdraw sulfur and replace it with oxygen.

There is a theory that an alien race is terraforming Earth through the emissions of our internal combustion engines and the resultant global warming.

[edit] See also

• Globus Cassus
• Extrasolar planets
• Weather control

[edit] References

[edit] External links

This article or section may contain spam. Wikipedia spam consists of external links promoting sites which exist primarily to sell goods or services, use objectionable amounts of advertising, or require payment to view the relevant content. If you are familiar with the content of the external links, please help by removing promotional links in accordance with Wikipedia:External links. (You can help!)

• Red Colony
• Terraformers Society of Canada
• Visualizing the steps of solar system terraforming
• Research Paper: Technological Requirements for Terraforming Mars
• An approach to terraforming Venus
• The Terraforming Information Pages
• The Terraforming of Worlds (pdf)