Terraforming of Mars
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Since the origin of the idea of terraforming, or changing a planet's environment to produce a world that is habitable by humans, one of the primary subjects of study for potential terraforming has been the planet 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 much of its water and atmosphere again unless prevented, possibly to the same processes that reduced it to its current state, although geological time scales are far longer than those needed for terraforming or subsequent climate maintenance.
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[edit] Background
It is thought that Mars did once 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 relatively low gravity of Mars likely contributed to the loss of lighter gases to space. The lack of plate tectonics on Mars is another likely factor, preventing the recycling of gases locked up in sediments back into the atmosphere. The lack of a magnetosphere surrounding Mars may have allowed the solar wind to contribute to eroding the atmosphere, although that effect is also active on Venus, but has not prevented that planet from having far greater atmospheric pressure than Earth. 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 not precisely clear. 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 maintenance activities.
Terraforming Mars would entail two major interlaced changes: building up the atmosphere and heating it. Since a thicker atmosphere of carbon dioxide and/or some other greenhouse gases would trap incoming solar radiation, and increased heat would in turn increase erosion and chemical activities on the surface, resulting in more outgassing and evaporation, the two processes would augment one another.
[edit] Adding heat
Mirrors made of thin aluminized PET film could be placed in orbit around Mars to increase the total insolation it receives.[1] This would increase the planet's temperature directly, and also vaporize water and carbon dioxide to increase the planet's greenhouse effect. Directing such reflected sunlight at the polar caps would maximize the effectiveness of this method.
While producing halocarbons on Mars 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 especially powerful greenhouse gases, and are stable for lengthy periods of time in atmospheres. They could be produced by genetically engineered aerobic bacteria[citation needed] or by mechanical processors scattered across the planet's surface.
Changing the albedo of the Martian 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, once life forms exist that can survive and be metabolically active on Mars.
Thinking far into the future, (on the order of hundreds of millions of years) 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, Mars will warm up on its own, making terraforming easier. Alternatively, an already-terraformed Mars would provide an alternate home for humanity if Earth becomes uninhabitable (see Space and survival).
[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 (for example, by using very large nuclear thermal rockets for the purpose, using some of the ammonia itself as the reaction mass) and send them into Mars's atmosphere. Since ammonia is high in nitrogen (NH3) it might also take care of the problem of 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.[citation needed] In 1970 physicist Freeman Dyson proposed sending a self-replicating machine to Saturn's moon Enceladus, which in addition to producing copies of itself would also be programmed to manufacture and launch an enormous number of solar sail-propelled cargo spacecraft. These spacecraft would carry blocks of Enceladean ice to Mars.[2]
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. Mars would require a similar buffer gas component although not necessarily as much. Still, obtaining significant quantities of nitrogen, argon or some other comparatively inert 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.[citation needed] 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.[citation needed] 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 Martian 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] Building a shield against radiation
Another significant, and probably most over-looked 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. Terraforming involves making life viable on another world, and so long as that life is going to be exposed to high levels of radiation it will not be desirable. The lack of a magnetosphere is also thought to have caused the Martian atmosphere to become as thin as it is in the first place, the solar wind adding a significant amount of heating to the atmosphere's top layers which enables the atmospheric particles to reach escape velocity and leave Mars (essentially "blowing" the atmosphere away, though that particular word may 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.
On a longer timescale, and with the technology of the near 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. However, recent scientific evidence suggest that just a thick enough atmosphere like Earth's is enough to create a shielding effect in the absence of a magnetosphere. In the past, Earth regularly had periods where the magnetosphere changed direction and collapsed for some time. Some scientists believe that in the ionosphere, a magnetic shielding was created almost instantly after the magnetosphere collapsed.[3], a principle that applies to Venus as well and would also be the case in every other planet or moon with a large enough atmosphere.
[edit] See also
[edit] References
- ^ Terraforming Mars: A Review of Research (htm). Retrieved on 2006-04-28.
- ^ Dyson, Freeman J. (1979). Disturbing the Universe. New York: Harper and Row, 194-204.
- ^ Real Media file (RM). Retrieved on 2006-03-10.
