Terraforming of Mars

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Artist's conception of the process of terraforming Mars.

Terraforming of Mars is a hypothetical process of planetary engineering by which the surface and climate of Mars would be deliberately changed to make large areas of the environment hospitable to humans, thus making the colonization of Mars safer and sustainable.

There are a few proposed terraforming concepts, some of which present prohibitive economic and natural resource costs.[1] As of 2018 it is not feasible, using existing technology, to terraform Mars.[2] Any climate change induced in the near term is proposed to be driven by greenhouse warming produced by an increase in atmospheric CO2 and a consequent increase in atmospheric water vapor, but Mars does not retain enough carbon dioxide that could practically be put back into the atmosphere to warm it.[2] Importing greenhouse gases, although impractical, is a concept to be studied.[2]

Motivation and side effects

Illustration of plants growing in a Mars base.[3]

Future population growth, demand for resources, and an alternate solution to the Doomsday argument may require human colonization of bodies other than Earth, such as Mars, the Moon, and other objects. Space colonization will facilitate harvesting the Solar System's energy and material resources.[4]

In many respects, Mars is the most Earth-like of all the other planets in the Solar System. It is thought[5] that Mars had 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. Given the foundations of similarity and proximity, Mars would make one of the most plausible terraforming targets in the Solar System.

Side effects of terraforming include the potential displacement or destruction of indigenous life, even if microbial, if such life exists.[6][7][8][9]

Challenges and limitations

The Martian environment presents several terraforming challenges to overcome and the extent of terraforming may be limited by certain key environmental factors.

Low gravity and pressure

The surface gravity on Mars is 38% of that on Earth. It is not known if this is enough to prevent the health problems associated with weightlessness.[10]

Mars's CO
2
atmosphere has about 1% the pressure of the Earth's at sea level. It is estimated that there is sufficient CO
2
ice in the regolith and the south polar cap to form a 30 to 60 kilopascals [kPa] (4.4 to 8.7 psi) atmosphere if it is released by planetary warming.[1] The reappearance of liquid water on the Martian surface would add to the warming effects and atmospheric density,[1] but the lower gravity of Mars requires 2.6 times Earth's column airmass to obtain the optimum 100 kPa (15 psi) pressure at the surface.[11] Additional volatiles to increase the atmosphere's density must be supplied from an external source, such as redirecting several massive asteroids containing ammonia (NH
3
) as a source of nitrogen.[1]

Breathing on Mars

Current conditions in the Martian atmosphere, at less than 1 kPa (0.15 psi) of atmospheric pressure, are significantly below the Armstrong limit of 6 kPa (0.87 psi) where very low pressure causes exposed bodily liquids such as saliva, tears, and the liquids wetting the alveoli within the lungs to boil away. Without a pressure suit, no amount of breathable oxygen delivered by any means will sustain oxygen-breathing life for more than a few minutes.[12][13] In the NASA technical report Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects, after exposure to pressure below the Armstrong limit, a survivor reported that his "last conscious memory was of the water on his tongue beginning to boil".[13] In these conditions humans die within minutes unless a pressure suit provides life support.

If Mars' atmospheric pressure could rise above 19 kPa (2.8 psi), then a pressure suit would not be required. Visitors would only need to wear a mask that supplied 100% oxygen under positive pressure. A further increase to 24 kPa (3.5 psi) of atmospheric pressure would allow a simple mask supplying pure oxygen.[14][clarification needed] This might look similar to mountain climbers who venture into pressures below 37 kPa (5.4 psi), also called the death zone, where an insufficient amount of bottled oxygen has often resulted in hypoxia with fatalities.[15]

Countering the effects of space weather

Mars does not have an intrinsic global magnetic field, but the solar wind directly interacts with the atmosphere of Mars, leading to the formation of a magnetosphere from magnetic field tubes.[16] This poses challenges for mitigating solar radiation and retaining an atmosphere.

The lack of a significant magnetosphere is thought to be one reason for Mars's thin atmosphere. Solar wind–induced ejection of Martian atmospheric atoms has been detected by Mars-orbiting probes, indicating that the solar wind has stripped the Martian atmosphere over time. While Venus has a dense atmosphere, it has only traces of water vapor (20 ppm) as it lacks a large, dipole induced, magnetic field.[16][17][18] Earth's ozone layer provides additional protection. Ultraviolet light is blocked before it can dissociate water into hydrogen and oxygen.[19]

Restoring the Martian magnetic poles or providing a sufficiently large artificial magnetosphere between the Sun and Mars is considered essential to restoring the Martian atmosphere and flowing liquid water.[18]

Advantages

Hypothetical terraformed Mars

According to scientists, Mars exists on the outer edge of the habitable zone, a region of the Solar System where liquid water on the surface may be supported if concentrated greenhouse gases could increase the atmospheric pressure.[1] 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, although the details of such a process are still not well understood.[20][21]

There are strong indications that Mars once had an atmosphere as thick as Earth's during an earlier stage in its development, and that its pressure supported abundant liquid water at the surface.[22] Although water appears to have once been present on the Martian surface, ground ice currently exists from mid-latitudes to the poles.[23][24] The soil and atmosphere of Mars contain many of the main elements crucial to life, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon.[25]

Any climate change induced in the near term is likely to be driven by greenhouse warming produced by an increase in atmospheric carbon dioxide (CO
2
) and a consequent increase in atmospheric water vapor. These two gases are the only likely sources of greenhouse warming that are available in large quantities in the Mars environment.[26] 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. Significant amounts of water are located at the south pole of Mars, which, if melted, would correspond to a planetwide ocean 5–11 meters deep.[27][28] Frozen carbon dioxide (CO2) at the poles sublimes 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 400 km/h (250 mph).[citation needed][original research?] This seasonal occurrence transports large amounts of dust and water vapor into the atmosphere, forming Earth-like clouds.[29]

Most of the 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.[30] 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.[31] Electrolysis could be employed to separate water on Mars into oxygen and hydrogen if sufficient liquid water and electricity were available.[citation needed]

Proposed methods and strategies

Comparison of dry atmosphere
Atmospheric
property
Mars Earth
Pressure 0.6 kPa (0.087 psi) 101.3 kPa (14.69 psi)
Carbon dioxide (CO2) 96.0% 0.04%
Argon (Ar) 2.1% 0.93%
Nitrogen (N2) 1.9% 78.08%
Oxygen (O2) 0.145% 20.94%
Artist's conception of a terraformed Mars centered on the Tharsis region
Artist's conception of a terraformed Mars. This portrayal is approximately centered on the prime meridian and 30° north latitude, 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 the left, Aonia Terra at the bottom, Terra Meridiani at the lower right, and Arabia Terra at the upper right. Rivers that feed the ocean at the lower right occupy what are now Valles Marineris and Ares Vallis and the large lake at the lower right occupies what is now Aram Chaos.

Terraforming Mars would entail three major interlaced changes: building up the magnetosphere, building up the atmosphere, and raising the temperature. The atmosphere of Mars is relatively thin and has a very low surface pressure. Because its atmosphere consists mainly of CO2, a known greenhouse gas, once Mars begins to heat, the CO2 may help to keep thermal energy near the surface. Moreover, as it heats, more CO2 should enter the atmosphere from the frozen reserves on the poles, enhancing the greenhouse effect. This means that the two processes of building the atmosphere and heating it would augment each other, favoring terraforming. It will be difficult to keep the atmosphere together, due to lack of a global magnetic field.[citation needed]

Importing ammonia

One intricate method uses ammonia as a powerful greenhouse gas. It is possible that large amounts of it exist in frozen form on minor planets orbiting in the outer Solar System. It may be possible to move these and send them into Mars's atmosphere.[32]

Importing hydrocarbons

Another way to create a Martian atmosphere would be to import methane or other hydrocarbons,[33][34] 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.[35]

Use of fluorine compounds

Because 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.[11][26] These gases are proposed for introduction because they produce a greenhouse effect many times stronger than that of CO2. This can conceivably be done by sending rockets with payloads of compressed CFCs on collision courses with Mars.[30] When the rockets crash onto the surface they would release their payloads into the atmosphere. A steady barrage of these "CFC rockets" would need to be sustained for a little over a decade while Mars changes chemically and becomes warmer. However, their lifetime due to photolysis would require an annual replenishing of 170 kilotons,[11] and they would destroy any ozone layer.[11]

In order to sublimate the south polar CO2 glaciers, Mars would require the introduction of approximately 0.3 microbars of CFCs into Mars's atmosphere. This is equivalent to a mass of approximately 39 million metric tons. This 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 estimate the elemental presence of fluorine in the bulk composition of Mars at 32 ppm by mass vs. 19.4 ppm for the Earth.[11]

A proposal to mine fluorine-containing minerals as a source of CFCs and PFCs is supported by the belief that because these minerals 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, C12F27N) to maintain Mars at 'comfortable' temperatures, as a method of maintaining an Earth-like atmosphere produced previously by some other means.[11]

Use of orbital mirrors

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 Mars'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 CO
2
ice sheet and contribute to the warming greenhouse effect.[1]

Albedo reduction

Reducing the albedo of the Martian surface would also make more efficient use of incoming sunlight.[36] This could be done by spreading dark dust from Mars's 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.[citation needed] 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. The conversion process to produce oxygen is highly reliant upon water. The CO2 is mostly converted to carbohydrates.[37] On April 26, 2012, scientists reported that lichen survived and showed remarkable results on the adaptation capacity of photosynthetic activity within the simulation time of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the German Aerospace Center (DLR).[38][39]

Funded research: ecopoiesis

The Mars Ecopoiesis Test Bed showing its transparent dome to allow for solar heat and photosynthesis, and the cork-screw system to collect and seal Martian soil together with oxygen-producing Earth organisms. Total length is about 7 centimetres (2.8 in).

Since 2014, the NASA Institute for Advanced Concepts (NIAC) program and Techshot Inc are working together to develop sealed biodomes that would employ colonies of oxygen-producing cyanobacteria and algae for the production of molecular oxygen (O2) on Martian soil.[40][41][42] But first they need to test if it works on a small scale on Mars.[43] The proposal is called Mars Ecopoiesis Test Bed.[44] Eugene Boland is the Chief Scientist at Techshot, a company located in Greenville, Indiana.[40] They intend to send small canisters of extremophile photosynthetic algae and cyanobacteria aboard a future rover mission. The rover would cork-screw the 7 cm (2.8 in) canisters into selected sites likely to experience transients of liquid water, drawing some Martian soil and then release oxygen-producing microorganisms to grow within the sealed soil.[40][45] The hardware would use Martian subsurface ice as its phase changes into liquid water.[43] The system would then look for oxygen given off as metabolic byproduct and report results to a Mars-orbiting relay satellite.[42][45]

If this experiment works on Mars, they will propose to build several large and sealed structures called biodomes, to produce and harvest oxygen for a future human mission to Mars life support systems.[45][46] Being able to create oxygen there, would provide considerable cost-savings to NASA and allow for longer human visits to Mars than would be possible if astronauts have to transport their own heavy oxygen tanks.[46] This biological process, called ecopoiesis, would be isolated, in contained areas, and is not meant as a type of global planetary engineering for terraforming of Mars's atmosphere,[42][46] but NASA states that "This will be the first major leap from laboratory studies into the implementation of experimental (as opposed to analytical) planetary in situ research of greatest interest to planetary biology, ecopoiesis, and terraforming."[42]

Research at the University of Arkansas presented in June 2015 suggested that some methanogens could survive in Mars's low pressure.[47] Rebecca Mickol found that in her laboratory, four species of methanogens survived low-pressure conditions that were similar to a subsurface liquid aquifer on Mars. The four species that she tested were Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, and Methanococcus maripaludis.[47] Methanogens do not require oxygen or organic nutrients, are non-photosynthetic, use hydrogen as their energy source and carbon dioxide (CO2) as their carbon source, so they could exist in subsurface environments on Mars.[47]

Protecting the atmosphere

One key aspect of terraforming Mars is to protect the atmosphere (both present and future-built) from being lost into space. Some scientists hypothesize that creating a planet-wide artificial magnetosphere would be helpful in resolving this issue. According to two NIFS Japanese scientists, it is feasible to do that with current technology by building a system of refrigerated latitudinal superconducting rings, each carrying a sufficient amount of direct current.[48]

In the same report, it is claimed that the economic impact of the system can be minimized by using it also as a planetary energy transfer and storage system (SMES).

Another study proposes the deployment of a magnetic dipole shield at the Mars L1 Lagrange point, therefore creating an artificial magnetosphere that would protect the whole planet from solar wind and radiation.[18]

Magnetic shield on L1 orbit

Magnetic shield on L1 orbit around Mars

During the Planetary Science Vision 2050 Workshop[18] in late February 2017, NASA scientist Jim Green proposed a concept of placing a magnetic dipole field between the planet and the Sun to protect it from high-energy solar particles. It would be located at the L1 orbit at about 320 R. The field would need to be "Earth comparable" and sustain 50000 nT as measured at 1 Earth-radius. The paper abstract cites that this could be achieved by a magnet with a strength of 1–2 teslas (10,000–20,000 gauss).[49] If constructed, the shield may allow the planet to restore its atmosphere. Simulations indicate that within years, the planet would be able to achieve half the atmospheric pressure of Earth. Without solar winds stripping away at the planet, frozen carbon dioxide at the ice caps on either pole would begin to sublimate (change from a solid into a gas) and warm the equator. Ice caps would begin to melt to form an ocean. The researcher further argues that volcanic outgassing,[dubious ] which to some degree balances the current atmospheric loss on Earth, would replenish the atmosphere over time, enough to melt the ice caps and fill ​17 of Mars' prehistoric oceans.[50][51][18]

Thermodynamics of terraforming

The overall energy required to sublimate the CO2 from the south polar ice cap was modeled by Zubrin and McKay in 1993.[1] If using orbital mirrors, an estimated 120 MW-years of electrical energy would be required in order to produce mirrors large enough to vaporize the ice caps. This is considered the most effective method, though the least practical. If using powerful halocarbon greenhouse gases, an order of 1000 MW-years of electrical energy would be required to accomplish this heating. However, if all of this CO2 were put into the atmosphere, it would only double[26] the current atmospheric pressure from 6 mbar to 12 mbar, amounting to about 1.2% of Earth's mean sea level pressure. The amount of warming that could be produced today by putting even 100 mbar of CO2 into the atmosphere is small, roughly of order 10 K.[26] Additionally, once in the atmosphere, it likely would be removed quickly, either by diffusion into the subsurface and adsorption or by re-condensing onto the polar caps.[26]

The surface or atmospheric temperature required to allow liquid water to exist has not been determined, and liquid water conceivably could exist when atmospheric temperatures are as low as 245 K (−28 °C; −19 °F). However, a warming of 10 K is much less than thought necessary in order to produce liquid water.[26]

In popular culture

The novel series by Kim Stanley Robinson known as the Mars trilogy chronicles the colonization and terraforming of Mars. The novels are titled according to the dominant color in the stage of terraforming achieved in each volume: Red Mars (1992), when Mars is still in its natural state; Green Mars (1993), when plants are able to grow in the atmosphere; and Blue Mars (1996), when the atmospheric pressure and temperature have risen high enough for seas and rivers to form.

The 1993 space trading and combat game Frontier: Elite II, as well as its sequels Frontier: First Encounters (1995) and Elite Dangerous (2014), feature a terraformed Mars.

The 1997 PC Real-time strategy game Dark Colony is based on a human-terraformed Mars, featuring a war between the colonizing humans and invading aliens of various life forms, with much use of biological warfare. The aliens try to colonize the terraformed planet for its resources.

The 2009 video game Red Faction: Guerrilla is set on a partially terraformed Mars, in which human beings are able to walk and breathe in the open without pressure suits or breathing apparatus.

The 2015 Japanese anime series Mobile Suit Gundam: Iron-Blooded Orphans features a terraformed Mars as the primary setting of the series. The concept of terraformed Mars is commonly used in the Gundam series, such as Gundam Age.

See also

References

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  3. ^ [1]
  4. ^ Savage, Marshall Thomas (1992). The Millennial Project: Colonizing the Galaxy in Eight Easy Steps. Little, Brown and Company. ISBN 978-0-316-77163-4.
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  7. ^ The Ethical Dimentsions of the Space Settlement Martyn J. Fogg.
  8. ^ The Ethics of Terraforming – Valencia Ethics Review
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  51. ^ "NASA Considers Magnetic Shield to Help Mars Grow Its Atmosphere". Popular Mechanics'.

External links

  • NASA – Aerospace Scholars: Terraforming Mars at the Wayback Machine (archived September 15, 2007)
  • Recent Arthur C Clarke interview mentions terraforming
  • Red Colony
  • Terraformers Society of Canada
  • Research Paper: Technological Requirements for Terraforming Mars
  • Peter Ahrens The Terraformation of Worlds
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