Terraforming, or Earth-shaping, is a theoretical process of modifying a planet's atmosphere to make it habitable for humans. In the case of Mars, terraforming would require artificial thickening of the atmosphere to intensify the process of greenhouse warming (heating the frozen landscape), ice melting to increase the H2O content of the atmosphere (creating water clouds) and greatly increasing the O2 density to ultimately make the atmosphere breathable.
Mars and the "Triple Point" of water
Presently, ice on Mars sublimes as the atmospheric pressure is so low, ice bypasses the liquid phase when heated. Sublimation occurs allowing ice to turn directly into gas (steam). One of the main challenges for future terraforming efforts would be to increase the atmospheric pressure significantly so water can exist as a liquid on the surface of Mars. The atmospheric pressure and ambient temperature will therefore need to be greater than the triple point of water (thereby existing as ice, liquid and gas). This is just above 0C and 600 Pa. Mars atmospheric pressure is already above 600 Pa. However, close to the triple point, water takes very little energy to turn into a gas, so higher pressures would be required in practice.
A life supporting atmosphere needs to contain a "buffer gas", such as nitrogen. Mars is currently lacking in nitrogen, but nitrogen could be sourced from Venus, Saturn's moon Titan, or from comets. Mars could be warmed up using greenhouse gases such as perfluorocarbons, which are stable in the atmosphere for long periods of time. Mirrors could be placed in orbit to increase the amount of insolation Mars receives.
Other greenhouse gasses include sulfur hexafluoride and 1,1,1-Trichloro ethane. These are very stable and highly effective greenhouse gasses. Use of such gasses to warm the atmosphere would allow the Carbon dioxide frozen into the polar caps and some of the water to evaporate adding to the mass of the atmosphere.If 4 hundredths of a microbar of manufactured greenhouse gas is needed to warm Mars to the point of runaway greenhouse effect, then a mass of manufactured greenhouse gasses equal to about 5.73 times the cargo capacity of the Edmund Fitzgerald every week for twenty years would be required for the project.
Certain organisms, such as archaea, lichen, and tardigrades have been proven capable of surviving extreme environments, such as the vacuum of space. They could gain a foothold on the martian surface after minimal terraforming. The byproducts of their metabolism would contribute to the terraforming efforts.
Long term prospects
The ultimate results of terraforming are disputed. Terraforming may have only a temporary effect, even if the effect lasts for some hundred or thousand years. Eventually, the solar wind may carry away most of the new atmosphere due to the insufficient magnetic fields of Mars. It has been suggested that the cost of terraforming a planet would be prohibitive, however to a growing population on the surface of that planet it would most likely be considered a normal colonial function to ensure that daily colonial endeavours have a positive effect on the atmosphere. Artificial magnetic fields might also be created around Mars to reduce atmospheric losses to space. And the solar system contains sufficient resources to replenish martian atmosphere indefinitely, but at a significant energy cost. Building space habitats might be a more practical long term objective for human occupation of space.
|Parameter||Mars, mbar||Plants, mbar||Humans, mbar|
|Total pressure||0.30-11.55 (6 average)||>10||>250|
|Carbon dioxide (CO2)||0.29-11.09 (5.76 average)||>0.15||<10|
|Nytrogen (N2)||0.01-0.22 (0.114 average)||>1-10||-|
While full terraforming to make Mars atmosphere suitable for breathable condition for humans can take around 100,000 years, transformations to the atmosphere suitable for plants could take from 100 to several thousands years. Current requirements for plants to grow on Mars are based on atmospheric pressure. Mars polar caps have enough CO2 to provide 100 mbar (10 kPa) additional atmospheric pressure to the existing 6 millibars. This would be enough to create sustainable growth condition for plants.
To make using pressure suit unnecessary for humans, atmospheric pressure needs to rise to at least 250 mbar (25 kPa) or 25% of Earth atmospheric pressure. This might be composed of 50 mbar of CO2, 60 mbar of water vapour and 130 mbar of Oxygen (minimal requirement oxygen pressure).
This would require extraction some part of the regolith deposits of CO2 which are estimated to be able to contribute 300 mbar of additional pressure, but require significantly greater time to extract. A 550 mbar atmosphere composed primarily of CO2 with a high fraction of oxygen would have then been achieved.
- Mahaffy, P. R.; Webster, C. R.; Atreya, S. K.; Franz, H.; Wong, M.; Conrad, P. G.; Harpold, D.; Jones, J. J.; Leshin, L. A.; Manning, H.; Owen, T.; Pepin, R. O.; Squyres, S.; Trainer, M.; Kemppinen, O.; Bridges, N.; Johnson, J. R.; Minitti, M.; Cremers, D.; Bell, J. F.; Edgar, L.; Farmer, J.; Godber, A.; Wadhwa, M.; Wellington, D.; McEwan, I.; Newman, C.; Richardson, M.; Charpentier, A. - Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover, Nature 341, pp. 263-266. DOI:10.1126/science.1237966
- Christopher P. McKay, Owen B. Toon & James F. Kasting - Making Mars habitable, Nature 352, pp. 489-496. DOI:10.1038/352489a0