Terraforming
Terraforming ( borrowed from the Latin terra and English forming for "[transformation] to [replacement] earth " or " earth transformation " for short) is the transformation of other planets into habitable, earth-like celestial bodies using future technologies. Planets or moons should be reshaped in such a way that human life is possible with little or no additional technical effort.
The term goes back to the science fiction novel Collision Orbit by Jack Williamson in 1942 and was later taken up by science.
The limits of habitability
The limits of habitability are estimated by McKay as follows:
| parameter | Limits | Value on earth | Comments on limits |
|---|---|---|---|
| Global temperature | 0-30 ° C | 15 ° C | |
| Plants only | |||
| Total pressure | > 10 hPa | 1000 hPa | Water vapor pressure + O 2 , N 2 , CO 2 |
| Carbon dioxide | > 0.15 hPa | 0.39 hPa | Lower limit of photosynthesis ; no clear upper limit |
| nitrogen | > 1–10 hPa | 800 hPa | Nitrogen fixation |
| oxygen | > 1 hPa | 200 hPa | Herbal breathing |
| People | |||
| Air mixture | > 500 hPa <5,000 hPa |
1000 hPa | Corresponds to 5.5 km above sea level on earth mountains with nitrogen anesthesia |
| Carbon dioxide | <10 hPa | 0.39 hPa | Limited by CO 2 poisoning |
| nitrogen | > 300 hPa | 800 hPa | Buffer effect |
| oxygen | > 130 hPa <300 hPa |
200 hPa | Lower limit due to shortness of breath, upper limit due to fire hazard and toxicity |
Venus
Starting conditions
Temperatures of more than 450 ° C and a pressure of around 92,000 hPa prevail on the surface of Venus . Any known form of organic life would immediately char. In addition, the days on Venus are very long (243 Earth days). Even if it were possible to reduce the greenhouse effect, outside the polar regions there might be strong temperature fluctuations between day and night.
Another problem is the heat capacity of the rock jacket . Even if, after a few centuries, the atmosphere had been artificially lowered to temperatures that would be tolerable for humans, the surface of the rocks would still be around 400 ° C - and the cooling could take centuries more.
The atmosphere of Venus consists mainly of CO 2 . At an altitude of around 50 km, temperatures between 20 ° C and 100 ° C (depending on the altitude) and the air pressure of a few (earth) atmospheres prevail. At this altitude there are clouds containing sulfuric acid (poisonous for many known living beings).
Water and temperature inversion
There is also a temperature inversion on Venus (see tropopause on Earth ).
A layer of cold air (−60 ° C) lies on earth at an altitude of 9 to 17 kilometers. This leads to the fact that water vapor condenses or freezes there. That is why the layers of the atmosphere above are extremely dry. As a result, very little water in the upper layers is split by UV radiation . As a result, very little water ( hydrogen ) escapes from the earth into space.
The temperatures on Venus are too high, however, so that water vapor is cooled down but not liquid. The atmosphere is very dense, so it can absorb a lot of water vapor. The hydrogen gains buoyancy. In this way, enormous amounts of hydrogen are constantly being carried off into space by the solar wind . As a result, Venus lost a large part of its water supply.
Methods for Venus
Terraforming could be done , for example, by introducing green algae into the CO 2 -rich atmosphere. This is supposed to lead to an enrichment of oxygen while at the same time reducing the greenhouse effect through the consumption of CO 2 through photosynthesis of the algae. The water required for this would have to be obtained from the decomposition of sulfuric acid or by capturing comets. Without water, however, the sulfuric acid is too concentrated today. In addition, although sulfuric acid is produced as a metabolic end product of earthly bacteria, there are no known organisms that use it as food and break it down.
In the higher atmospheric layers, pressure and temperature are moderate. So there could be more favorable conditions for floating plants, air plankton so to speak. The chemical conditions are characterized by the high content of sulfuric acid. The green algae idea does not seem to be directly feasible, because the conditions for the survival of the plants would have to be created by these very plants. However, it is conceivable that the algae produce water and hydrocarbons from sulfuric acid and CO 2 and thus convert them into their biomass. Such algae are not known on earth, especially since they would have to exist in a largely waterless environment.
If Venus came below the critical point of 374 degrees, water would become liquid under the high pressure and rain out. This would eliminate the greenhouse effect of water vapor, which is said to be around 20 times as effective as CO 2 . In addition, the liquid water would also reflect additional heat into space. Before that, however, the temperatures would rise even further due to the released water, which is another obstacle to the terraforming of Venus.
In connection with colonization , the construction of airship-like , floating stations in the high atmosphere of Venus, and perhaps also the cultivation of floating, balloon-like plants as food, is also conceivable. The floating cities could - according to Robert Zubrin - be connected with shields that would cast a shadow and thus cool the planet. In addition, these shields could be made from carbon, which is locally abundant in the atmosphere. In terms of terraforming, Venus remains an extremely difficult planet.
The floor of Venus probably contains large amounts of simply oxidized metals (FeO, MgO, CaO, ...). It is still unclear why the substances in the regolith (Venus soil) did not react in large quantities with carbon dioxide (CaO + CO 2 → CaCO 3 ). Carbonates are not stable in the sulfuric acid environment.
It has been suggested to plow the ground vigorously in order to bind larger quantities of the greenhouse gas through a carbon sink .
Mars
Starting conditions
- The existing atmospheric pressure is 0.75% of the terrestrial pressure.
- The temperatures on the surface fluctuate (depending on the proximity of the pole or equator) between −85 ° C and +20 ° C
- The atmosphere consists of 95% CO 2 .
- As long as the planetary magnetic field is absent, Mars can not permanently hold an atmosphere under the influence of the solar wind . As soon as the inner core has solidified, the lack of a dynamo effect means that a magnetic field no longer forms.
The following changes would be necessary for Mars to develop into what is known as a "second earth":
- The surface temperature would have to be increased by around 60 Kelvin .
- The density of the atmosphere would have to be increased. The lower limit would be 300 hPa, depending on the gas mixture, which corresponds to 1/3 of the pressure on earth. A 1000 hPa (1 bar) dense atmosphere would mean, due to the lower gravity, that the atmosphere would be almost three times as high as on Earth. The nitrogen reserves of Mars are estimated to be low; Estimates only speak of an amount of 100–300 hPa nitrogen. It may also have deposited mineral deposits.
- Liquid water would have to be made available (occurs automatically in a denser atmosphere).
- The proportion of O 2 ( oxygen ) and inert gases such as N 2 ( nitrogen ) in the atmosphere would have to be increased, whereby (a certain percentage of) nitrogen has the advantage that it enables plants to live, but any other would also be inert Gas (or gas mixture such as nitrogen with xenon) is conceivable.
- One would have to design the atmosphere in such a way that it has a tropopause in the deeper layers, which holds the water trapped below them. This effect protected the earth from drying out. In contrast to Venus, where even the coldest layers are not below 0 ° C, so that the water does not rain down and penetrates further into the higher layers. There it is then photodissociated and the hydrogen is blown into space by the solar wind .
Methods for Mars
In Mars , terraforming can begin with carbon dioxide (CO 2 ), which is stored in large quantities in the polar ice. Estimates comprise about 300 to 600 hPa (or English mb ). Larger amounts (450–900 hPa) of CO 2 are bound in the regolith . This could theoretically create a dense atmosphere containing carbon dioxide, but which is toxic to humans. Even plants can only tolerate an amount of around 50 hPa CO 2 . However, it is known that algae feel comfortable even in pure carbon dioxide atmospheres. Some types of algae even thrive best in pure CO 2 . Various methods are conceivable for initiating the greenhouse effect.
With all methods the following results are obtained through linked reactions:
- Denser atmosphere due to the released CO 2 . If this is sufficiently tight (about 1/3 of the earth's air pressure, which corresponds to the air pressure on Mount Everest ), there is no need for a pressure suit.
- Higher temperatures due to the greenhouse effect, resulting in further enrichment of the atmosphere due to the self-reinforcing melting of the Mars pole caps.
- Liquid water by increasing pressure and temperature.
- Liquid water forms carbonic acid under the influence of the carbon dioxide-rich atmosphere, which can dissolve CO 2 from the regolith .
- The carbonic acid could possibly extract nitrogen from the nitrate-rich minerals, thus enriching and thickening the atmosphere with nitrogen.
- The released water vapor is a good greenhouse gas (4 times the effectiveness of CO 2 ).
According to a scientific study supported by NASA and published in 2018, however, there is not enough carbon dioxide on Mars that could trigger a greenhouse effect in the atmosphere that would ensure living conditions.
Space mirror
A very complex and therefore costly method of supplying the required energy to the Martian environment would be to position several gigantic mirrors, so-called solettas, in a Mars orbit . The mirrors would each have a diameter of around 100 to 200 km and a mass of a few hundred thousand to a few million tons. The sunlight reflected by its surface, which is mirrored with the help of polymer-reinforced aluminum foil, is directed onto the icy polar regions and melted them. The resulting CO 2 emissions into the atmosphere would trigger a desired greenhouse effect that would further warm Mars.
asteroid
Manipulating the trajectory of an asteroid seems fantastic, but at least theoretically it is possible. An asteroid or comet with a high content of volatile substances ( volatiles ) is supposed to be guided to Mars by manipulating its trajectory and would release these substances when it entered the Martian atmosphere or when it hit the surface. In doing so, he activated a self-reinforcing greenhouse effect, analogous to the other methods. The likely high water content of a comet would also bring large amounts of water vapor into the atmosphere. The enormous impact caused by this could also release additional underground water reservoirs. Although this method is not yet technically feasible, it could be available at the point in the future when terraforming should be carried out on Mars.
soot
The simplest method of warming Mars is to distribute soot or other light-absorbing substances over the ice or dry ice surfaces of the polar caps. The stronger absorption of light causes a rise in temperature that causes the ice or dry ice to sublime.
Microbes
In addition, very "early" during terraforming, microbes , bacteria from the earth could settle on Mars, which can exist under low pressure, with little or no sunlight and without oxygen (such as on earth in volcanoes , on the sea floor or in Sulfur springs ). There is also the idea that microbes with pigments, i.e. dark cell membranes - distributed over the poles - could melt the ice, since dark colors heat up better in the light than light ones.
Partial terraforming
The melting of the polar ice caps (which consist of both dry and water ice) could create a significantly denser atmosphere, but it would consist almost exclusively of carbon dioxide. Of the Viking probes is known that the Marsregolith releases under the influence of carbon dioxide and water large amounts of oxygen. The regolith seems to be a possible source of oxygen here. The question, however, is whether there is enough water on Mars and how this could be released into the Martian atmosphere. Although carbon dioxide is a greenhouse gas, even a complete release of all carbon dioxide in the form of dry ice and the regolith from 1,000 to 2,000 hPa would probably not be enough to raise the temperature by the necessary 60 Kelvin. Other, more effective greenhouse gases such as CFCs (whereby CFCs destroy a possible ozone layer) or octafluoropropane (it has 7,000 times the global warming potential of carbon dioxide, is stable for over 2,600 years and can coexist with an ozone layer without damage) would have to be added in large quantities to achieve this mark permanently and make liquid water possible. Higher humidity would also increase the greenhouse effect. The "import" of asteroids with a high proportion of methane and ammonia could also lead to more greenhouse-effective gases.
At the end of this process, Mars would be warmer, more humid and surrounded by a dense carbon dioxide atmosphere, as it may have existed 3.5 to 4 billion years ago. Since this process can be set in motion purely chemically and does not require any biological processes, this could be achieved in a relatively short time of 100 to 1,000 years. In the end, the prerequisites for earthly plant growth would be given and people would be able to stay outdoors (when using an oxygen mask ).
Complete terraforming
For complete terraforming, the high carbon dioxide content would have to be reduced, which should take significantly longer periods of time. This could be reduced by plants to such an extent that it is breathable for humans. However, since carbon dioxide also contributes to the greenhouse effect, a reduction would also lead to a cooling again. In order to prevent this, greenhouse gases would have to be introduced here to offset this effect. In addition to the oxygen, the atmosphere should also receive a buffer gas in significant quantities. On earth, this buffer gas is nitrogen, which makes up almost 80 percent of the earth's atmosphere. The proportion on Mars should not be that high, but should at least correspond to the amount of oxygen. However, it is questionable whether there is enough nitrogen on Mars. In addition to nitrogen, argon or other inert gases could also serve as a substitute or in combination (whereby a minimum proportion of nitrogen would have to be present in order to ensure plant growth).
criticism
Critics have called the terraforming theories unrealistic for several reasons:
- None of the planets theoretically considered for terraforming has been sufficiently researched to be able to make even halfway well-founded statements.
- None of the processes that are intended to bring about terraforming has so far been understood to such an extent that the effects of the methods can be predicted with sufficient accuracy.
- The temporal, material and energetic dimensions of terraforming go beyond any acceptable framework for a western industrial culture.
- Furthermore, it remains unclear whether Mars could hold the atmosphere mobilized in this way or whether, for example, through the forced thawing, the remnants of the water that remained there would also evaporate into space and ultimately the planet even less through so-called terraforming. habitable ”. In addition, Mars has no magnetic field worth mentioning, which means that the particle radiation of the solar winds would "wash away" the gas molecules unchecked.
- Moving entire machinery or huge plants such as mirrors, methane or CFC-producing factories is beyond reach; Transporting a buggy, a small water tank and a five-man crew to the moon is the current limit of what is feasible. The consumption of all of mankind's available energy supplies today would bring a fraction of the required materials into orbit.
- It makes no sense to think about making foreign planets habitable as long as it is not even possible on earth to colonize the comparatively life-friendly, but almost uninhabited areas in deserts and steppes in an economically meaningful way. In fact, not even the opposite process has stopped; desertification and desertification are continuing.
- There are also ethical and ecological arguments against terraforming, since a possibly existing ecosystem would be destroyed by terraforming. This dilemma may be a. set out in the science fiction novel Red Mars , which shows the right of an alien environment to be preserved. Before doing so, research would have to be carried out to determine whether ecosystems have developed there - and whether they would thrive or even die off at higher temperatures.
- The purely economic dimension of terraforming has so far hardly been explored, which is likely to be a necessary condition for making resources available for terraforming. Put more simply, how much does it cost to transport a ton of material to Mars?
- Questions of ownership and use of the terraformed space have not yet been clarified, both formally and legally.
Paraterraforming
Precisely because of the complexity of a complete terraforming, the concept of a para- or pseudoterraforming , also called worldhouse (from the English ' worldhouse [concept] ' ; further translated as word house [-concept ] ), has emerged.
With paraterraforming, a habitable habitat is built that enables free breathing. Structures of this kind are usually thought to be significantly larger than currently common air domes and consist of a roof one to several kilometers high, which is attached by towers and cables, enclosed airtight and provided with a breathable atmosphere. In principle, there is also the possibility of inflating a protective cover merely with the aid of the overpressure prevailing inside and without support, just like an air dome. The overpressure would be necessary anyway, since the pressure is unsuitable or too low for human life in relation to a non-existent or very thin atmosphere (similar to Mars ). In such cases, the cables and towers served more to keep the structure on the ground than to keep it from collapsing.
Paraterraforming could be realized more quickly and expanded in a modular manner as required, from a small region to the encompassing of an entire planet. Supporters of this concept claim that this can already be achieved with today's technology. After all, the amount of gases is not required as in the actual terraforming, but only a small part. Due to its modularity, it can also be implemented on asteroids that cannot hold any atmosphere.
However, a major disadvantage is the effort required for construction and maintenance. A world house would also be at risk from leaks. This could be reduced by sectioning and security mechanisms. The hazard from meteorites also comes into play.
Paraterraforming can, however, also be used as a supplement and intermediate step to complete or partial terraforming, in which individual regions that can be inhabited by humans are surrounded by a world house, while the rest of the planet has been transformed with traditional terraforming to such an extent that sufficient pressure and temperature are required There is breathing for plants.
Attempts to develop an autonomous ecosystem on earth were made in the projects Biosphere 2 and Biosphere 3 .
Other options
Another option to use hostile places (planets, asteroids, etc.) is not to terraform the place, but to adapt it to people - by changing their physique through genetic engineering , biotechnology ( cyborg, etc.). Examples would be adapting the organs to low gravity , increasing lung volume for atmospheres with lower oxygen concentrations , an exoskeleton for high pressure ratios, and the like.
However, apart from the currently existing biotechnical implementation difficulties, enormous resistance to implementation is likely to be mobilized, especially due to the psychological effects. In addition, the field of application would still be limited, since no celestial body in question has problems for which the solutions mentioned would be sufficient according to current ideas.
See also
- Geoengineering can be seen as terraforming the earth
- Colonization of Venus
- Lunar colonization
- Mars colonization
- Saturn's moon Titan , the only moon in the solar system with a dense atmosphere
- Darwin experiment on Ascension Island . Researchers today see this as the first successful terraforming experiment.
Web links
- What is terraforming? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Nov 7, 1999.
- Terraforming - Der Mars - German Space Society ( page no longer available )
- Terraforming - How to make a planet habitable - Christoph Kulmann , 1997; Terraforming Mars ( Memento from November 13, 2010 in the Internet Archive )
- Worldhouse concept (English)
Individual evidence
- ↑ C. McKay, J. Kasting, O. Toon: Making Mars Habitable (English) - Nature (Edition 352), August 8, 1991, pp. 489-496.
- ^ A b Mark A. Bullock, David H. Grinspoon: The stability of climate on Venus. In: Journal of Geophysical Research: Planets. 101, 1996, p. 7521, doi: 10.1029 / 95JE03862 ; See also PDF ( Memento of the original from September 20, 2004 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ KR Sridhar, JE Finn, MH Kliss: In-situ resource utilization technologies for Mars life support systems. ( Memento of September 2, 2006 in the Internet Archive ) (English) - Adv Space Res; 25 (2), 2000, pp. 249-55. PMID 11542809
- ↑ Technological Requirements for Terraforming Mars (English) - SAO / NASA ADS Astronomy Abstract Service , June 1993, bibcode : 1993jpmc.confX .... Z ; see also users.globalnet.co.uk
- ↑ 5. Summary and outlook ( Memento of the original from October 3, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. - Terraforming - Mars. P. 8; German Space Society ; u. a. with "[...] and plants not much more than 50 millibars." (accessed on October 2, 2016).
- ↑ Heise Newsticker: NASA: Terraforming Mars is not possible with foreseeable means
- ↑ Entry for CAS no. 76-19-7 in the GESTIS substance database of the IFA , accessed on May 6, 2015 (JavaScript required)
- ^ Charles Darwin's ecological experiment on Ascension isle (English) - Howard Falcon-Lang for BBC News , on September 1, 2010.
