The Terra-forming of Mars is the hypothetical process by which the climate, surface and known properties of Mars would be deliberately changed with the goal of making it habitable by humans and other terrestrial life; and thus providing the possibility of safe and sustainable colonization of large areas of the planet.
Terra-forming is when you alter the current environment of a planet's topography to create a living and habitable biosphere.
Based on experiences with Earth, the environment of a planet can be altered deliberately; however the feasibility of creating an unconstrained planetary biosphere is undetermined. At present the economic resources required to execute such methods as are required for terraforming are far beyond that which any government or society is willing to allocate to such a purpose. An open source space colonization strategy may be the only viable solution under the current economic climate.
Reasons for Terraforming
In the not-too distant future, population growth and demand for resources may create pressure for humans to colonize new habitats such as the surface of the Earth's oceans, the sea floor, near-Earth orbital space, the moon and nearby planets, as well as mine the solar system for energy and materials. Thinking far into the future (in 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, because all main sequence stars brighten slowly throughout their lifetimes. When this happens, it will become imperative for humans to migrate away to areas farther from the sun if they have any hope of surviving. Through terraforming, humans could make Mars habitable long before this 'deadline'. Mars could then be in the habitable zone for a while, giving humanity some thousand additional years to develop further space technology to settle on the outer rim of the solar system, before Mars becomes uninhabitable due to the sun's increasing heat.
Ascension Island style Terraforming
Ascension Island style terraforming is terraforming by implanting suitable species, without any prior violent geological alterations. On Mars, trenches and craters do have sufficient atmospheric pressure to give water some liquidity range, and seasonal liquid water do occur in such places at the warmer latitudes.
Plants need some amount of oxygen to germinate and survive the night, and the soil on Mars contains corrosive hydrogen peroxide, but it is possible to "turn lemons into lemonade" by implanting bacteria capable of producing catalysts that speed up the transformation of hydrogen peroxide into water and oxygen. There are many different types of bacteria, and even if no species can do it, it could still be solved by genetically engineering bacteria. If Mars is warmed first, even this may not be necessary since it is known that oxygen levels on Earth increased sharply at the end of Snowball Earth, most likely because of the hydrogen peroxide-derived oxygen stored in the ice over millions of years of ultraviolet radiation that was suddenly released when the ice melted. That makes the soil livable for tough plant species as well as producing oxygen enough for plants to germinate and survive the night (and for insects and worms to breathe). To keep the soil good, the bacteria should be engineered in a way that makes the catalysts fairly persistent, enough to last a whole Martian freeze season. The oxygen would also form a rudimentary ozone layer as well as shielding against much ionizing radiation due to the denser atmosphere. That denser atmosphere would also widen the range where liquid water can exist at the warmer latitudes during the warmer seasons, so the bacteria in question could spread throughout the tropics barring high mouintains.
The next step is implanting suitable plant species. The plants would have to be fairly UV tolerant because of the still rudimentary ozone layer, but such plants do grow in mouintainous regions on Earth. There is not enough atmospheric CO2 on Mars for the plants to convert into a human-breathable atmosphere (and trying would remove a precious greenhouse gas, probably eliminating the tepid season altogether), but that can be solved by introducing genetically engineered mykorrhiza fungi capable of extracting CO2 from minerals, which they then provide into the roots of the plants. That would, apart from of course releasing oxygen, turn mineral carbon into biomass carbon, founding an ecosystem that can survive without plate tectonics. It is possible that such ecosystems exist naturally on exoplanets without plate tectonics, an argument against the Rare Earth hypothesis.
Warmer temperatures can be achieved by introducing plants and animals that produce strong greenhouse gasses such as methane and nitrous oxide.
Terraforming Mars would require building up the atmosphere and keeping it warm. Mars has a very thin atmosphere thus very low surface pressure (0.6 kPa). 95% of Mars' atmosphere is carbon dioxide, 3% is nitrogen and 1.6% is argon, it contains traces of oxygen, water and methane. Since its atmosphere consists mainly of CO2, a known greenhouse gas, once the planet begins to heat, more CO2 enters the atmosphere from the frozen reserves on the poles, adding to the greenhouse effect. This means that the two processes of building the atmosphere and heating it would augment one another, favoring terraforming. However, on a large scale, controlled application of certain techniques over enough time to achieve sustainable changes, would be required to make this theory a reality.
As to how to achieve the warming, many ideas have been suggested. Some have suggested using very strong greenhouse gases like CFC, but they have the disadvantage of being ozone-destroying. A cocktail effect of many more moderate greenhouse trace gases like methane, ammonia and nitrous oxide may do it (different greenhouse gases blocks different parts of the infrared heat radiation spectrum, making their combined effect much stronger than the sum of the gases). The production of such gases can, after successful terraforming, be kept going by organisms and keep the planet warm. Another solution would be satellites (mirror, lens or prism) focusing light on the poles, heating them to release the frozen CO2. It would also be possible to warm the frozen CO2 by covering the poles in albedo-lowering black pigments (preferably small particles to spread over large surfaces but heavy to sink into the polar caps as they vaporize instead of blowing away, in other words high density black particles). The "painting" can be combined with light focusing. "Painting" can also be applied to areas with much water ice or even generally over Mars. In the latter case, the particles would blow all over the place and making them heavy would be less important.
Building the Atmosphere
To build the atmosphere on Mars, We would need the importation of water (not necessarily since there is lots of frozen water on Mars). Adding water as well as heat would be the key of changing this dry world into a world suitable for life. Depending on the level of carbon dioxide in the atmosphere, importation and reaction of hydrogen would produce heat, water and graphite. Alternatively, reacting hydrogen with the carbon dioxide atmosphere would make methane and water. Another way is importation of methane or other hydrocarbons, that are usual in Titan's atmosphere. The methane could be vented into the atmosphere where it would act to compound the greenhouse effect.
Just like oxygen levels increased abruptly at the end of Earth's snowball period, most likely due to hydrogen peroxide-derived oxygen stored in the ice over millions of years of ultraviolet radiation and released suddenly when the ice melted, so would a thawing of Mars be likely to immediately produce an oxygen-rich atmosphere. However, photosynthesis would be important for keeping the atmosphere oxygen-rich in a longer run. That may not be a problem, since the combined elimination of hydrogen peroxide from the soil and formation of an oxygen-rich atmosphere with some degree of ozone layer would make it much easier to introduce plants.
Retaining the Atmosphere
There's no point in spending time, money, and resources building up an atmosphere on Mars if it's just going to blow away. Even to this day, solar wind is still blowing away what little atmosphere the Red Planet has left.
Mars is geologically dead. The core solidified a long time ago. Without a dynamo in the core, Mars has no magnetic field.
There are various ways to fix the magnetic field problem, and maybe we should do that before taking any other steps in the terraforming process (though the atmospheric loss is slow, so postponing the magnetic field a few centuries past terraforming does hardly any harm at all). The first, and easiest way would be to place a network of artificial satellites in orbit around Mars to generate and create an artificial magnetic field. That would, however, require the function of the satellites and should mostly be considered a preliminary solution.
The other, "impossible" way would be to start up the core again. Planting nuclear bombs in the center of Mars would not blow the planet apart since no known nuke is strong enough to overcome the mass and gravity of Mars. Nuking Mars core into action could be done by serially inserting many relatively small devices and blowing them up one by one and not simultaneously, which is also more realistic in terms of manufacturing. The radioactive material produced would stay in the core and help a more long-term heating similar to that in Earth's core. One other way would be to put large, dense objects in orbit around Mars and heat the planet via tidal forces. Mars already has two such objects: Phobos and Deimos. That's not enough. We might need Ceres, in addition to a few more asteroids. However, not only mass matters but also orbital eccentricity, so even just making the orbits of Phobos and Deimos more eccentric may do the trick. And even if that is not enough, the imported worlds need not be as big as Ceres, as long as they are made eccentric enough. Manipulated spacetimes would be another way to create tides. Sonic or artificial "seismic" waves could also be used to create friction heating inside Mars.
In the future, if we terraform Mars or other popular planets, there will be people who do not want these planets to be terraformed (for issues such as the natural preservation, or preserving possible undiscovered alien life), and people who do may spark conflict between them and the people who want to terraform.
Another argument is, "We've nearly destroyed our own planet. Why destroy another?"
The anti-congestion argument counter-criticisms the conflict notion as well as the myth of Humans being inherently destructive, but it does not counter-criticism environmental conservation.
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