The terraforming 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, thus providing the possibility of safe and sustainable colonization of large areas of the planet. The concept is reliant on the assumption that the environment of a planet can be altered through artificial means; the feasibility of creating an unconstrained planetary biosphere is undetermined. There are several proposed methods, some of which present prohibitive economic and natural resource costs, and others which may be currently technologically achievable.[1]
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In many respects, Mars is the most earthlike of all the other planets in our Solar System. Indeed, it is thought that Mars once did have 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.
Future population growth and demand for resources may necessitate human colonization of objects other than Earth, such as Mars, the Moon, and nearby planets. Space colonization will facilitate harvesting the Solar System's energy and material resources.[2]
Additionally, In the event of a catastrophic extinction event, such as the meteor believed to have killed off the dinosaurs 65 million years ago, Earth's species, including humans, could live on this second habitable planet.
Further, in approximately 7.6 billion years the Sun will enter a red giant phase, as the hydrogen fuel in its core is completely consumed causing the Sun's core to contract and the outer layers to expand. At this point, the Sun's upper atmosphere will extend as far as 1.2 AU, out past the present orbit of the Earth.[3] This expansion will likely destabilize the orbits of the inner planets, causing them to spiral inwards toward the sun and be destroyed.
It is speculated that Earth will be out of its habitable zone before the Sun enters its Red Giant phase.[3] Astronomers estimate that the Sun will be 33% more luminous in three billion years. The warming Sun and increased solar radiation will cause the Earth's oceans to evaporate, and the Earth to eventually become molten again. The habitable zone would move farther out from the Sun, giving potential Mars colonists some thousands of additional years to develop further space technology to settle elsewhere in the Milky Way.
Martian soil contains many minerals that could theoretically be used for terraforming. Large amounts of water ice exist below the Martian surface, as well as on the surface at the poles, where it is mixed with dry ice, frozen CO2. It has been found that significant amounts of water are stored in the south pole of Mars, and if all of this ice suddenly melted, it would form a planetwide ocean 11 meters deep.[4] Frozen carbon dioxide (CO2) at the poles sublimates into the atmosphere during the Martian summers, and small amounts of water residue are left behind, which fast winds sweep off the poles at speeds approaching 250 mph (400 km/h). This seasonal occurrence transports large amounts of dust and water vapor into the atmosphere, giving potential for Earth-like cirrus clouds.
Most of the elemental oxygen in the Martian atmosphere is present as carbon dioxide (CO2), the main atmospheric component. Molecular oxygen (O2) only exists in trace amounts. Large amounts of elemental oxygen can be also found in metal oxides on the Martian surface, and in the soil, in the form of per-nitrates.[5] An analysis of soil samples taken by the Phoenix lander indicated the presence of perchlorate, which has been used to liberate oxygen in chemical oxygen generators. Electrolysis could be employed to separate water on the planet into oxygen and hydrogen if sufficient liquid water and electricity were available.
It has been suggested that Mars once had an environment relatively similar to that of Earth during an earlier stage in its development.[6] While water once appears to have existed on the Martian surface, it now only appears to exist at the poles and just below the planetary surface as permafrost. The lack of both a magnetic field and geologic activity on Mars may be a result of its relatively small size, which allowed the interior to cool more quickly than Earth's, though the details of such a process are still not well understood.
| Mars | Earth | |
|---|---|---|
| Pressure | 0.6 kPa (0.087 psi) | 101.3 kPa (14.69 psi) |
| Carbon dioxide (CO2) | 95.32% | 0.04% |
| Nitrogen (N2) | 2.70% | 78.08% |
| Argon (Ar) | 1.60% | 0.93% |
| Oxygen (O2) | 0.13% | 20.94% |
Terraforming Mars would entail three major interlaced changes: building up the atmosphere, keeping it warm, and keeping the atmosphere from being lost into outer space. The atmosphere of Mars is relatively thin and thus has a very low surface pressure of 0.6 kilopascals (0.087 psi) and a pressure of 0.003 kilopascals (0.00044 psi) at the top of Olympus Mons (22 kilometres (14 mi)); compared to Earth with 101.3 kilopascals (14.69 psi) at sea level and 4.0 kilopascals (0.58 psi) at an altitude of 22 kilometres (14 mi). The atmosphere on Mars consists of 95% carbon dioxide (CO2), 3% nitrogen, 1.6% argon, and contains only traces of oxygen, water, and methane. Since its atmosphere consists mainly of CO2, a known greenhouse gas, once the planet begins to heat, the (CO2) may help lock the heat inside. Moreover, as the planet heats, more CO2 should enter the atmosphere from the frozen reserves on the poles, compounding 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 (explained below) over enough time to achieve sustainable changes would be required to make this hypothesis a reality.
An important step in building the martian atmosphere would be the importation of water, which can be obtained, for example, from ice asteroids or from ice moons of Jupiter or Saturn, beyond the water ice already present at the Martian north pole. Another important step for building the atmosphere is keeping the atmosphere while building it. Artificially creating a magnetosphere would assist with this; see the section below on "Magnetic field and solar radiation" for the benefits of a magnetosphere.
There is presently enough carbon dioxide (CO2) as ice in the Martian south pole and absorbed by regolith (soil) around the planet that, if sublimated to gas by a climate warming of only a few degrees, would increase the atmospheric pressure to 300 millibars,[7] comparable to twice the altitude of the peak of Mount Everest. While this would not be comfortably breathable by humans, it would eliminate the present need for pressure suits, melt the water ice at Mars' north pole (flooding the northern basin), and bring the year-round climate above freezing over approximately half of Mars' surface. This would enable the introduction of plant life, particularly plankton in the new northern sea, to start converting the atmospheric CO2 into oxygen.
Another, more intricate, method uses ammonia as a powerful greenhouse gas (as it is possible that large amounts of it exist in frozen form on asteroidal objects orbiting in the outer Solar System); it may be possible to move these (for example, by using very large nuclear bombs to blast them in the right direction) and send them into Mars' atmosphere.[8] Since ammonia (NH3) is high in nitrogen it might also take care of the problem of needing a buffer gas in the atmosphere. Sustained smaller impacts will also contribute to increases in the temperature and mass of the 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. 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 is difficult.
Another way would be to import methane or other hydrocarbons,[9][10] which are common in Titan's atmosphere (and on its surface). The methane could be vented into the atmosphere where it would act to compound the greenhouse effect.
Methane (or other hydrocarbons) also can be helpful to produce a quick increase for the insufficient martian atmospheric pressure. These gases also can be used for production (at the next step of terraforming of Mars) of water and CO2 for the Martian atmosphere, by reaction:
CH4 + 4 Fe2O3 => CO2 + 2 H2O + 8 FeO
This reaction could probably be initiated by heat or by Martian solar UV irradiation. Large amounts of the resulting products (CO2 and water) are necessary to initiate the photosynthetic processes.
Hydrogen importation could also be done for atmospheric and hydrospheric engineering.[11] For example, hydrogen could react with iron(III) oxide from the Martian soil, which would give water as a product:
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. Alternatively, reacting hydrogen with the carbon dioxide atmosphere via the Sabatier reaction would yield methane and water.
Since long-term climate stability would be required for sustaining a human population, the use of especially powerful fluorine-bearing greenhouse gases possibly including sulfur hexafluoride or halocarbons such as chlorofluorocarbons (or CFCs) and perfluorocarbons (or PFCs) has been suggested.[12] These gases are the most cited candidates for artificial insertion into the Martian atmosphere because of their strong effect as a greenhouse gas. This can conceivably be done relatively cheaply by sending rockets with payloads of compressed CFCs on collision courses with Mars.[5] When the rockets crash onto the surface they release their payloads into the atmosphere. A steady barrage of these "CFC rockets" would need to be sustained for a little more than a decade while the planet changes chemically and becomes warmer.
In order to sublimate the south polar CO2 glaciers, Mars would require the introduction of approximately 0.3 microbars of CFCs (chloro-fluoro-carbons) into Mars' atmosphere. CFCs are powerful greenhouse gases that are thousands of times more effective at warming than CO2. The 0.3 microbars needed would mass approximately 39 million metric tons, which is about three times the amount of CFC manufactured on Earth from 1972 to 1992 when CFC production was banned by international treaty. Mineralogical surveys of Mars have found significant amounts of the ores necessary to produce the amount of CFC gas required.
A proposal to mine fluorine-containing minerals as a source of CFCs and PFCs is supported by the belief that since the quantities present are expected to be at least as common on Mars as on Earth, this process could sustain the production of sufficient quantities of optimal greenhouse compounds (CF3SCF3, CF3OCF2OCF3, CF3SCF2SCF3, CF3OCF2NFCF3) to maintain Mars at 'comfortable' temperatures, as a method of maintaining an Earth-like atmosphere produced previously by some other means.[12]
Adding heat and conserving the heat present is a particularly important stage of this process, as heat from the Sun is the primary driver of planetary climate. As the planet would become warmer through various methods the CO2 on the polar caps would sublime into the atmosphere and would further contribute to the warming effect. The tremendous air currents generated by the moving gasses would create large, sustained dust storms, which would heat (through absorbing solar radiation) the molecules in the atmosphere.
Mirrors made of thin aluminized PET film could be placed in orbit around Mars to increase the total insolation it receives.[1] This would direct the sunlight onto the surface and could increase the planet's surface temperature directly. The mirror could be positioned as a statite, using its effectiveness as a solar sail to orbit in a stationary position relative to Mars, near the poles, to sublimate the CO2 ice sheet and contribute to the warming greenhouse effect.
Reducing the albedo of the Martian surface would also make more efficient use of incoming sunlight.[13] This could be done by spreading dark dust from Mars' moons, Phobos and Deimos, which are among the blackest bodies in the Solar System; or by introducing dark extremophile microbial life forms such as lichens, algae and bacteria. The ground would then absorb more sunlight, warming the atmosphere.
If algae or other green life were established, it would also contribute a small amount of oxygen to the atmosphere, though not enough to allow humans to breathe.
Another way to increase the temperature could be to direct small cosmic bodies (asteroids) onto the Martian surface; the impact energy would be released as heat and could vaporize Martian water ice to steam, which is also a greenhouse gas. Asteroids could also be chosen for their composition, such as Ammonia, which would then disperse into the atmosphere on impact, adding greenhouse gases to the atmosphere. Lightning may have built up nitrate beds in the soil over the life of the planet.[7] Impacting asteroids on these nitrate beds would release additional nitrogen and oxygen into the atmosphere.
Earth abounds with water because its ionosphere is permeated with a magnetic field. The hydrogen ions present in its ionosphere move very fast due to their small mass, but they cannot escape to outer space because their trajectories are deflected by the magnetic field. Venus has a dense atmosphere, but only traces of water vapor (20 ppm) because it has no magnetic field. The Martian atmosphere also loses water to space.
Earth's ozone layer provides additional protection. Ultraviolet light is blocked before it can dissociate water into hydrogen and oxygen. Since little water vapor rises above the troposphere and the ozone layer is in the upper stratosphere, little water is dissociated into hydrogen and oxygen.
Mars would be uninhabitable to most life-forms due to high solar radiation levels. Because of the planet's lack of a magnetosphere, the Sun is thought to have thinned the Martian atmosphere to its current state; the solar wind adding a significant amount of energy to the atmosphere's top layers which enables the atmospheric particles to reach escape velocity and leave Mars. Indeed, this effect has even been detected by Mars-orbiting probes. Another theory is that solar wind rips the atmosphere away from the planet as it becomes trapped in bubbles of magnetic fields called plasmoids.[14]
Venus, however, shows that the lack of a magnetosphere does not preclude a dense (albeit dry) atmosphere. A thick atmosphere could also provide protection against solar radiation to the surface, similar to Earth's. In the past, Earth has regularly had periods where the magnetosphere changed direction and collapsed for some time.[15]
The lack of a protective magnetic field would also have possible health effects on colonists due to increased cosmic ray flux. The health threat depends on the flux, energy spectrum, and nuclear composition of the rays. The flux and energy spectrum depend on a variety of factors, which are incompletely understood. The Mars Radiation Environment Experiment (MARIE) was launched in 2001 in order to collect more data. Estimates are that humans unshielded in interplanetary space would receive annually roughly 400 to 900 milli-Sieverts (mSv) (compared to 2.4 mSv on Earth) and that a Mars mission (12 months in flight and 18 months on Mars) might expose shielded astronauts to ~500 to 1000 mSv.[16] These doses approach the 1 to 4 Sv career limits advised by the National Council on Radiation Protection and Measurements for Low Earth orbit activities.
Shielding from cosmic rays can be accomplished by placing habitation modules either within lava tubes or under igloo structures built from sintered regolith bricks.[17]
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