Some Ideas Regarding the Biological Colonization of The Planet Mars
written by DAN RĂZVAN POPOVICIU on October 08, 2006 | contact me
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Far from being a purely theoretical science, Biology has many practical applications. This science will have a huge importance for the future of humanity. What can Biology bring to mankind? There are three main answers:
Health— Biological sciences will play an important role in fighting various infectious agents (viruses, bacteria), in curing other diseases (cancer, for example) and in "repairing" wounded tissues, thus increasing people’s life expectancy.
Food— Considering the rapid demographic growth, the traditional food sources will become insufficient for feeding Earth’s population. Biologists will have the duty to search for organisms that are more nourishing and easier to be cultivated (algae, crustaceans etc.), and also to improve the species already cultivated, in order to increase their productivity, their nutritiousness and their resistance to pests.
Space— While the human demographical growth is unlimited, our planet’s resources are limited. Mankind will have to conquer and colonize the extraterrestrial space. We know that none of the planets in our Solar System has the natural conditions necessary to human colonization. The solution is to modify these conditions and to gradually implant terrestrial life forms on these planets, in order to create habitats for the future colonists.
This essay is regarding the latter subject.
The idea of implanting terrestrial life on other planets (a process called terraformation, ecopoiesis, ecosynthesis) appeared during the first half of the twentieth century in science-fiction literary works. Nowadays, more and more scientists are trying a scientific approach to this issue. The terraformation of various celestial bodies in the Solar System is an interdisciplinary problem, implicating sciences like Astronomy, Physics, Chemistry, Biology etc. It will require different solutions, from one planet to another.
This essay will treat the case of planet Mars, the closest, from all points of view, to Earth. Also, it will focus mostly on the biological aspects of terraformation.
2. MARS: PREMISES FOR TERRAFORMATION
A. Natural conditions
Mars belongs to the group of the luric planets, together with Mercury, Venus and Earth. From all the planets of the Solar System, it is situated at the shortest distance from Earth. Its diameter is slightly larger than half of our planet’s diameter. Its orbit is exterior to Earth’s orbit. The rotation period is of 24 hours and 40 minutes (a martian day is almost equal to a terrestrial one) and the duration of the revolution movement (the martian year) is 687 days. Mars has seasons, like our planet. Because the distance from the Sun is longer, Mars receives only 43% of the sunlight that reaches Earth. The gravitational force is 38% of the terrestrial one. The planet has no magnetic field and no tectonic activity. There is, instead, some volcanic activity.
The atmosphere is extremely rarefied, having a pressure of only 7.4-10 millibars (0.8% of the terrestrial one). The lack of a magnetic field causes the continuous erosion of the atmosphere by the solar wind. The martian atmosphere is composed of CO2 (95%), N2 (2.7%), Ar (1.6%), O2 (0.13%) and other gases, in negligeable quantities (CO, H2O, Ne, Kr, Xe, O3).
The average temperature is about -60ºC, but temperatures can vary between -75ºC and +25ºC, according to the latitude and season. By comparison, the average temperature on Earth is about +15ºC.
The quantity of ultraviolet radiations that reaches the surface of Mars is much larger than on Earth, being deadly for almost any life form.
The relief forms are inequaly distributed on the surface of the planet. The southern hemisphere has high altitudes, with many impact craters, volcanic mountains and three large depresions: Hellas, Argyre and Isidis (probably huge craters). The northern hemisphere has, predominantly, low altitudes. There are two polar caps composed of frozen water and carbon dioxide. There is no liquid water on the planet’s surface.
The upper layer of the martian crust, a few kilometers thick, is called regolith and is composed of rocks, dust and ice. It is, probably, porous (due to the low gravity). The entire planet’s surface is covered with a red dust.
The samples taken by the Mars Pathfinder mission from the surface, together with the analyses of several meteorites, of martian origin, show the following chemical composition:
Probably, the analyses must be redone for K2O and MnO2. This composition is similar to that of the terrestrial rocks, except for the iron compounds, much more abundant on Mars. In the primary rocks iron is found in its reduced form (Fe2+), and in the soil, in its oxidized form (Fe3+). The predominant minerals at the surface are haematite (Fe2O3), jarosite (KFe3(OH)6(SO4)2), goethite (FeO(OH)). It seems that the upper layer of the regolith contains oxidizing agents.
Apparently, the environmental conditions on Mars are improper to any living organisms. However, there are more and more evidence that indicate these conditions were not always the same. Most scientists think that, in the past, there was liquid water on Mars and, obviously, the temperatures were higher and the atmosphere was denser. This poses a problem: where and why most of the martian atmosphere disappeared? There are two theories. One of them says that the planet lost its atmosphere due to violent impacts with other celestial bodies (comets, asteroids). In this case the atmospheric gases were lost in space and trying to recompose the martian atmosphere would be almost impossible with our current technical means. The second theory says that the atmosphere was slowly eroded, during geological eras, by the solar wind, after the volcanic activity slowed down, causing the atmospheric gases to stop recycling. This way, most of the gases would have infiltrated, under various forms, into the martian crust. If this theory is true, there is a big chance that the planet’s atmosphere could be modified, allowing the implantation of life on Mars.
B. Resources for terraformation
Planet Mars has, under various forms, all the chemical elements necessary to life.
The most obvious water reserves on Mars are located in the polar caps. According to some estimations, these contain around 5,000 km3 of water (equivalent to a 4 cm layer on the entire planet’s surface).
It seems that other water reserves exist in some stratified deposits (alternate layers of dust and ice) in the territories around the caps.
Apparently, there are, in the regolith, in the regions situated north and south of 40º latitude (North and, respectively, South), ice lenses (somehow similar to the terrestrial permafrost).
Squires and Carr (1986) estimated the total water quantity in the caps and regolith to the equivalent of a 13-100 m thick layer of liquid water on the entire planet.
Also, liquid water is supposed to exist in the lithosphere. Wittome says that the regolith, due to its porous structure, allowed water to infiltrate. This means that in the regions situated at more than 40º latitude, at a few kilometers depth, there sholud be thermal waters, at very high pressures. A recent model of the hydrological cycle on Mars (Clifford, 1993), shows that in the lower areas of the planet, there could be subterranean waters, at artesian pressures. Also, some minerals should contain water.
It is known that the polar caps contain solid carbon dioxide. Some of this sublimates during the martian summer and solidifies in the winter, causing variations of the caps’ area. Initially, it was thought that most of the southern cap was made of CO2 (estimated to the equivalent of 10-100 mbar of gaseous CO2). However, recent data show that this cap is composed mostly of water.
Also, it is estimated that the regolith contains large amounts of CO2. Zent et al. mentioned the equivalent of 30-40 mbar, while other estimations indicate as much as 300 mbar. Some chemical tests showed that the martian regolith is capable of absorbing large quantities of CO2.
On Mars, carbon is also found in carbonates (of calcium, iron, magnesium etc.). It was observed the existence of layered deposits (calcium carbonate sediments). It is supposed that these are located in former lakes and evaporation basins. Such deposits were also discovered in Valles Marineris (a huge canyon system). Based on the low value of the Ca/Si ratio in the regolith, Warren (1987) says that there are large amounts of CaCO3 on Mars (there is only a little calcium in the regolith because most of it is concentrated in carbonates). According to some estimations, the carbonate reserves should contain the equivalent of 30 mbar of gaseous CO2. The presence of CO2 is extremely important for modifying the environmental conditions on Mars, as it will be shown below.
Nitrogen is a vital element for every organism, being an important part of the composition of proteins, nucleic acids and other organic substances. The quantity of this element on Mars is unknown. This poses a big problem to those interested in the possibility of terraforming the planet. The atmospheric dinitrogen quantity is very small (2.7% of the atmosphere). Still it is preconized the existence of substantial amounts of nitrates in the regolith (according to some estimations, the equivalent of 300 mbar of gaseous N2), in former evaporation basins from the equatorial regions, together with the presence of underground ammonia deposits. Analyses done on martian basaltic meteorites show that these contain an amuont of nitrates and phosphates larger than the terrestrial basaltic rocks (scientists tried the experimental cultivation of some plants on soils containing martian meteoritic rocks, with spectacular results). Generally, it is accepted that there are important nitrate reserves on Mars, but their quantity is unknown.
Some specialists think there are some organic material deposits located at 3-40 meters below the planet’s surface (Bullock et al., 1994) or in the polar zones (Bada and McDonald, 1995).
In space, large amounts of organic compounds (especially hydrocarbons) are found in celestial bodies called carbonaceous chondrites (meteorites, asteroids, satellites). Still, it appears that on the planet’s surface there are no organic substances. This fact is probably due to the strong oxidizing agents in the upper layer of the regolith, that quickly oxidized the hydrocarbons, forming CO2. That is why, if there really is organic material on Mars, it should be found buried in the regolith. Also, the two natural satellites of the planet, Phobos and Deimos, belong to the carbonaceous chondrite class.
Recently, the Mars Express probe discovered some methane emissions of unknown origin.
According to spectrometric analyses, sulphur is found in the martian "soil" in 10-100 times higher concentrations than on Earth. It is found in the form of sulphates (like jarosite), extremelly abundant on Mars. On Earth, large reserves of sulphur compounds are associated with volcanic activity.
Spectrometric analyses for phosphorus could not be effectuated, but it is thought that this is abundant, as the composition of martian meteorites show.
Other elements, like iron, manganese, potassium etc., exist in large quantities on Mars.
Additional chemical and mineralogical analyses are needed in order to know the exact quantities and locations of the various substances necessary to ecopoiesis.
C. Conditions necessary to life
To the proper going of metabolic activities of terrestrial organisms, envinronmental temperatures higher than 0ºC are required, although there are organisms that can resist for a long time at negative temperatures. It is known that during the martian summer, in the equatorial regions, temperatures can grow up to +25ºC, but this is not enough.
Generally the atmospreric pressure should be higher than 10 mbar, although some plants and anaerobic bacteria can withstand pressures below one millibar. The partial pressure of CO2 must exceed 0.15 mbar (on Mars, it is much higher than this limit). O2 partial pressure must be higher than 1 mbar. Many anaerobic and even aerobic microorganisms can grow in pure CO2 atmospheres. Some cyanobacteria and algae like Cyanidium sp. or Scenedesmus sp. produce, by photosynthesis, the oxygen needed for their respiration and, in the dark periods, they become anaerobic (Seckbach, 1970). It was found out that in the cyanobacterial and algal colonies grown at high CO2 concentrations will appear mutants that require larger and larger concentrations of this gas (Spalding et al., 1983; Marcus et al., 1986). This way mutants could be selectionated for colonizing Mars. Plants need, for photosynthesis, 20-210 mbar of O2 (mythochondrial enzymes need oxygen) but can be adapted to as little as la 0.1 mbar. Nitrogen fixing bacteria can begin their activity at 5-10 mbar of N2. The solar light that received by Mars is more than sufficient for photosynthesis.
For humans, requirements are much higher. The atmosphere must have a mass three times larger than the terrestrial one, in order to compensate the low gravity. The atmospheric pressure must exceed 500 mbar (on Earth it is around 1,013 mbar, at the sea level). CO2 partial pressure needs to be below 10 mbar (otherwise, it becomes toxic). O2 pressure must be between 130 and 300 mbar (too little oxygen causes hypoxia, too much, causes combustion). Additionally 300 mbar of buffer-gas are needed. This is necessary to prevent combustion, due to the presence of O2 in the atmosphere. The ideal buffer-gas is N2 (on Earth, it constitutes more than three quarters of the atmosphere), but, between certain limits, it can be replaced by He, Ar, Ne, Kr,Xe, CH4, H2O, CO, HCN, SF6.
The terraformation of a planet has two stages. The first stage was called by specialists ecopoiesis or ecosynthesis and its finality is the implantation of the first life forms on the planet and the creation of self-regulating anaerobic ecosystems. The second stage is the true terraformation and consists of creating an aerobic biosphere that will allow humans to colonize the planet.
As shown above, the main factors that prevent life implantation on Mars are too low atmospheric pressure, too low temperatures, lack of a protection against ultraviolet radiation, lack of liquid water on the planet’s surface. For all these problems there is only one solution: greenhouse effect.
The greenhouse effect is based on the property of certain gases (called greenhouse gases) to retain the solar heat reflected by the planet’s surface. The solar radiation directly heats the surface. Without greenhouse gases, a large part of the resulting heat would be lost in space. The greenhouse gases absorb it, heat the atmosphere, the atmosphere heats furthermore the planetary crust and the cycle goes on.
The best-known greenhouse gas is CO2. This constitutes most of the martian atmosphere, but it is insuficient because of the low atmospheric pressure (although it appears that, indeed, Mars is going through a warming process). Still, as shown above, CO2 is, probably, quite abundant on Mars, either as carbonic ice or as carbonate deposits.
Ecopoiesis on Mars could be realized by a human mechanical intervention that would produce a chain reaction. An artificial heating would release CO2, that, through the greenhouse effect, would release other quantities of CO2, H2O (water vapor is a greenhouse gas), maybe NH3 etc.
Several mathematical models of a greenhouse effect on Mars were done. One of them, created by McKay et al., show that an artificial temperature growth of only 4ºC could sustain a chain reaction, causing the southern polar cap to completely melt down (an initial 25ºC impulse would be needed). The release of 800 mbar CO2 in the atmosphere would bring the average temperature on the planet to 250 K (-25ºC), compared to the actual 213 K (-60ºC). Releasing 2 bar CO2 would increase the temperature to 273 K (0ºC), and 3 bar CO2, to 280 K. The last estimations of the southern cap’s composition infirm the presence of such large amounts of CO2, but the model remains valid. The sublimation of the CO2 from the polar caps would be followed by the release of this gas from the regolith (where CO2 is more abundent than in the caps). An additional 10ºC increase is required (Zubrin, McKay), producing a chain reaction. Other amounts of CO2 can be released from the carbonate reserves, using more aggressive methods, as shown below.
Even if McKay’s previsions would prove to be too optimistic, temperatures on Mars would still increase enough to allow the colonization of terrestrial organisms. The presence, in the atmpsphere, of several hundred millibars of CO2 would have many effects. First, the total atmospheric pressure would increase to acceptable values. Then, the atmospheric temperature would increase, allowing the existence (temporary or even permanent) of liquid water, at least in the equatorial regions. Finally, an ozone layer would appear and it would absorb most of the deadly radiations that reach the surface. In the upper layers of the atmosphere, under the action of ultraviolet radiation, carbon dioxide, goes through a simple splitting reaction, producing ozone.
Linda and James Graham show that all that life needs in order to be implanted on Mars is 90-300 mbar CO2 and 2 mbar O3 (for protection against radiation). These objectives are perfectly realizable.
If the theory of ecopoiesis, shown above, is rather simple, its practical realization is more problematic. Several solutions were proposed:
A. Orbital mirrors
The artificial heating of the polar caps and of the regolith could be done by placing large mirrors on the planet’s orbit. These would reflect the sunlight towards certain areas on the planet (especially the southern cap), triggering the greenhouse effect.
A mirror with a diameter of 20 meters was already placed in orbit around Earth in the 1980’s (the "Znamia" project) in order to illuminate Russia’s northern territories during the polar night. It is preconized the launch, in the next future, of a mirror of 200 meters in diameter, with the same purpose. Most of the specialists say that a mirror that would heat enough the southern cap must have at least 125 kilometers in diameter (and a mass of about 200,000 tons). It would be built of aluminized mylar. The technology for building it is known, being the same as for producing the "solar sails" (that, in the future, will be used for the propulsion of spaceships). Its ideal location would be a stationary one, at the equilibrium point between the solar wind’s force and the planet’s gravitation.
Building such a mirror is not such a big problem (it would be the equivalent of Earth’s aluminium production for five days) but transporting it to the martian orbit is. Perhaps it should be built of small modules or replaced with many small mirrors. Using simultaneously more heating methods would greatly reduce the mirror's necessary dimensions.
B. Nuclear explosions
Using nuclear weapons to release carbon dioxide seems to be a easier solution for our current technological possibilities. Also, this would, finally, give Earth’s huge atomic arsenals a real utility for mankind.
Nuclear warheads could be used in two ways. First, they could be detonated at the planet’s surface, in the polar zones, in order to melt the caps. According to some estimations, it would be sufficient if, during four martian years (about seven terrestrial years), at the beginning of each martian spring, a nuclear warhead of 20 kilotons (thus, not a very powerful one) would be detonated in a dusty area near the southern cap, for the entire cap to melt. This would cumulate the direct effects of the explosion’s heat with the creation of dust storms that would cover the cap, reducing its albedo (this aspect will be discussed below). Probably, these estimations are too optimistic, but the idea is valid.
Second, subterranean nuclear explosions could be used to release greenhouse gases (CO2 and water vapor) from the carbonate deposits and from the "permafrost". Detonating nuclear warheads in nitrate deposits would release N2 and O2.
This solution is criticized for two main aspects. The first is the quantity of radiations that would appear after the explosions and that would make vast regions of the planet inhospitable to life. Yet, there are many ways of reducing the radioactive contamination. Using thermonuclear warheads (based on hydrogen fusion), that produce less radiations than fission weapons and detonating them, mostly, underground, would limit the afffected area. Also, it sould be considered the fact that terraformation would be a long process that will take, probably, tens of thousands of years. In this time, radioactivity would be greatly reduced, so that the future human colonists would not be affected. The second aspect, more problematic, is the number of nuclear warheads needed, which, according to some estimations, would be to big compared to the available atomic weapons.
C. Greenhouse gas production
Another solution is the artificial enrichment of the martian atmosphere in greenhouse gases. There are greenhouse gases much more efficient than carbon dioxide: halocarbons, ammonia, methane. Releasing these in the atmosphere in sufficient quantities would heat the planet and would sublimate the carbon dioxide, triggering the chain reaction necessary to ecopoiesis.
Chlorofluorocarbons (CFC), responsible of destroying the ozone layer on Earth, are extremely strong greenhouse gases. It is estimated that a very small concentration of CFC, of one part in a million, would be enough to heat the atmosphere with 60ºC.
Yet, they are useless on Mars, for two reasons. First, they would destroy the ozone layer, the only defense against radiations. Second, ultraviolet radiations photolise CFC. The life of CFC would be very short (estimations indicate something between a few days and several tens of years) and they should be produced continously.
Perfluorocarbons (PFC), as well as some sulphur compounds (SF6), are resistant to ultraviolet radiations and do not attack the ozone layer. Like the CFC, they are extremely strong greenhouse gases. For exemple, SF5CF5 is about 20,000 times more efficient than CO2 and has a lifespan of 3,500 years. The problem is that these gases are being known for a relatively short time and their degree of toxicity has not been exactly determined, and neither their absorbtion band (although some research has been done- Marinova).
Releasing these gases in the martian atmosphere would mean their production in situ and, thus, the existence on Mars of the necessary industrial instalations. The main problem is finding raw materials. Fluorine can be extracted from minerals like apatite and fluorite and then, in reaction with atmospheric CO2 would form PFC. It was calculated that, in order to release a quantity of halocarbons sufficient for raising the temperature by 5ºC, an energy of around 1,315 MW is needed, equal to that produced by an ordinary nuclear power plant (Zubrin, McKay).
Ammonia is a strong greenhouse gas. It is unlikely that it could be produced, in short time and in sufficient quantities, on Mars. It could be "imported" from other regions of the Solar System. Comets and some asteroids contain large amounts of ammonia.
Deviating these celestial bodies towards Mars would be a problem. Although not far from the planet’s orbit there is a large asteroid belt, it would be easier that asteroids containing NH3 to be brought from the regions beyond Pluto, because their revolution speed is lower and they are easier to deviate. Some of the ammonia that they contain could be used for propulsion. It was calculated that for transporting an asteroid of 10 billion tons (2.6 kilometers in diameter) constituted entirely of NH3 and situated at a distance of 12 astronomical units, four 5,000 MW thermonuclear propellers (tested since the 1960’s) would be enough. These would heat the asteroid, sublimating 8% of the ammonia quantity and using it for propulsion.
The transport would take ten years and would increase the temperature on Mars by 3ºC. In order to avoid causing great damage to the planet, the asteroid should not be crashed directly into the planet’s surface, but aerobraked.
Yet, the practical realisation of such transports would be quite difficult at the current technological level. Also, it is extermely improbable that an asteroid would be formed entirely of ammonia. Known asteroids and comets do not contain more than 10% ammonia.
Methane can be, in theory, "imported" from the Solar System, just like ammonia. Methanogen bacteria can also produce it. The current natural conditions on Mars do not allow the growth of such bacteria at the surface, but only, maybe, underground (where methane production would have little effect on the atmosphere, and methanogenesis would be very slow. Introducing methanogen bacteria would be possible only in a more advanced phase of ecosynthesis. Methane can be synthetised by reacting molecular hydrogen with atmospheric carbon dioxide, at high temperatures and with nickel catalyzers:
Finding a hydrogen source for this reaction would be problematic.
D. Using thermal waters
As shown above, the martian regolith is porous, due to the low gravitational force and, thus, permeable to water. This caused liquid water (which in the past was, probably, abundant on Mars) to infiltrate at various depths in the planet’s crust. Water temperature and pressure are high at great depths. Wittome says that at 6 km depth there should be water reserves at 300ºC. Also, colder water should exist at one kilometer depths, in the regions beyond 40º of latitude, especially in the Tharsis zone and, maybe, in Valles Marineris. If Clifford’s model was correct, the lowlands (mostly in the northern hemisphere) could have accesible subterranean waters.
In order to exploit these water reserves, drilling is required. Thermal waters could be used in many ways. They could be transported by pipelines to the ice deposits in the regolith contributing to their melting and releasing CO2. Acidified thermal waters could be used for dissolving carbonate deposits, forming CO2, and nitrate deposits, forming N2 and O2.
Due to its enormous pressure, water could be let to flush in the atmosphere, vaporizing itself (because of its high temperature and low atmospheric pressure) and coming back at the surface as snow. Due to impurities contained by subterranean water, this snow would have a darker colour and, if it falls on the polar caps, it would help reducing their albedo and melting them.
Thermal waters could be used for producing the electricity needed by other installations necessary to ecopoiesis (drills, PFC factories etc.).
Finally, if thermal waters were directed to the bottom of a crater or of a depression in the crust, a lake would appear. These lakes would be covered by an ice crust and, below it, liquid water. If such lakes were located in the equatorial regions, it would be possible that, during the summer, they would not be frozen. In these lakes, living organisms could be introduced, preparing them for the moment when the natural conditions at the surface would be suitable to life. There are cyanobacteria and unicellular algae that can grow and photosynthesize even under thin ice crusts. Various chemosynthesizing organisms could grow in these lakes. The existence of artificial thermal springs would favorize the growth of microorganisms, such as methanogen bacteria, that prefere this kind of habitats and that would produce methane, a strong greenhouse gas.
The main problem for exploiting thermal waters is that of transporting to Mars and keeping in function installations like drills, pipelines, power generators etc. There are quite many such devices needed for obtaining significant results. Knowing the exact location of the subterranean water reserves is also necessary.
E. Reducing the albedo
The word "albedo" means the amount of light reflected by a certain body. A low albedo means that the body absorbs more solar radiation and, thus, it heats more. The martian ice caps reflect much solar light. If their surface was covered with darker substances, their albedo would decrease and the ice would heat, allowing the carbon dioxide to sublimate.
The easiest way of doing so is by creating dust storms. As shown above, the planet’s surface is covered by a red dust (it is red because of the iron oxides). The red dust would cover areas of the polar caps, helping them to melt.
Furthermore, dust storms would have another importance for ecopoiesis. It was observed that the distribution of the small ozone quantity in the martian atmosphere varies with the season and latitude (Lindner, 1988). These variations can be as large as 40%. During the first stages of ecosynthesis, until a sufficiently thick ozone layer would be formed, these variations would let entire regions of the planet without protection against ultraviolet radiations. Dust storms, not only would help the chemical process of forming ozone, but would absorb themselves part of the radiations.
As shown above, reducing the albedo could also be done with the "dirty" snow produced by using thermal waters.
Another possibility would be reducing the general albedo of the planet. This way, Mars would absorb more solar radiations and the whole atmosphere would become warmer. This could be done by covering large areas of the martian surface with dark substances (such as hydrocarbons). As shown above, it is possible that, at various depths in the regolith, hydrocarbons would be found. However, locating and extracting them would pose big technical problems. Furthermore, their quantity is unknown and neither their lifespan in the oxidizing environment at the regolith’s surface.
It would be more economical to use the planet’s natural satellites. These have relatively small dimensions (they are probably former asteroids) and belong to the carbonaceous chondrites’ class, containing ice and black rocks, rich in hydrocarbons. Temperature at their surface is around 313 K (40ºC). Phobos has 22 kilometers in diameter. Its revolution speed around the planet is very high. Its orbit is continously closening to the planet and, in the far future, it will crash into Mars. Deimos has only 12.6 kilometers in diameter and a much lower revolution speed. Deviating and disintegrating these satellites in the martian atmosphere, using powerful nuclear explosions, would cover large territories with dark organic material. The impact of large satellite fragments (that, as shown above, have a high temperature) with the planet’s surface would release certain amounts of CO2 from the regolith, ausing, this way, a slight global warming.
The resulting organic material could become food for heterotrophic microorganisms, either under this form, either as intermediary products resulted after their oxidation by the regolith (salts of the acetic, oxalic, benzenocarboxilic acids etc.).
Pure carbon (black) can be obtained by reacting carbon dioxide with hydrogen, using, as catalyzers, iron, rubidium etc.:
Again, the problem is finding a hydrogen source.
These would be the main solutions for modifying the natural conditions on Mars. Of course, many other ones were proposed. For example, building small human colonies (isolated from the environment) and developing industrial activities capable of realising ecopoiesis. These colonies would also have artificial biospheres where organisms could be prepared for colonizing the planet. However this would take a long time and would pose technical problems.
Another idea would be building satellites that would receive solar energy and send it to the polar caps under another form (laser, microwaves).
As one could observe, for each of the solutions shown above, the technical requirements are relatively large. They would be reduced by using more, or even all of these methods, simultaneously. This way, the orbital mirrors needed would be smaller, so as the number of the nuclear warheads, of the drilling installations, or the amount of artificially produced greenhouse gases.
When can ecopoiesis start? As soon as possible, strictly depending of the technical means. When it would be over? There are various estimations. Generally, it is thought that one hundred years, or even less, would be enough for the first anaerobic ecosystems to be installed on Mars. After introducing the first organisms, the global warming due to human intervention, would continue until the martian atmosphere would have an acceptable pressure and temperature for superior organisms, including humans.
So, after triggering the greenhouse effect, another century would be necessary until life could be implanted on Mars. At that moment, Mars would have an atmosphere of several hundreds of millibars, formed mainly of CO2. An ozone layer would exist, that would defend the planet’s surface from radiations. Atmospheric movements would appear (winds, air currents). Temperatures would increase by several tens of degrees and would become acceptable to life.
In Antarctica, bacteria, cyanobacteria and algae were discovered, whose methabolic processes can take place at 258-273 K (-15-0ºC) during the polar summer and that hibernate during the winter, at temperatures as low as 213 K (-60ºC). There are lichens that photosynthesise at 249 K, can hibernate at 173 K and can make water reserves during the dry periods.
An increase of the average temperature means that, in the regions situated close to the equator, temperatures would be higher than 0ºC most of the year. The water that will begin melting, during the warm season, from the polar caps and from the ice reserves in the regolith, would flow, following the natural slopes, towards areas located closer to the equator (the three large craters, in the southern hemisphere and the territories near the demarcation line, in the northern hemisphere). This way, large areas with liquid water would appear, including the mineral rich regions near the volcanic zones (Tharsis). Water evaporation in the warm regions of the planet would initiate a hydrological cycle and would produce precipitations. Water would accumulate in depressions of the lithosphere, forming lakes (covered or not by ice crusts).
In a more advanced stage of the global warming process, in the northern hemisphere would appear an ocean that would cover as much as 10% of the planet’s surface and would have an average depth of about 70 meters (Hancox). The three large depressions in the southern hemisphere (Isidis, Argyre and Hellas) would become seas. These vast and shallow water basins would be an ideal environment for the growth of algae and other organisms. Also, a hydrographic network would appear (rivers).
Even since early stages of the global warming process, the first terrestrial organisms could be introduced on Mars. The implantation of life on the planet should take place gradually. The selection of the colonizer organisms should be done according to their resistance to the natural conditions on Mars at that moment and according to their utility for the terraforming process (i.e. to their role in the planetary biogeochemical cycles).
The final purpose of terraformation is bringing the natural conditions within tolerable limits for humans and creating a martian biosphere, capable of sustaining a large human population. The main functions that the living organisms should have on Mars, as synthetized by Julian Hiscox, are the following:
1) increasing the atmospheric pressure and changing its composition, by releasing CO2 from carbonates (Friedmann et al., 1993), N2 from nitrates (Hiscox and Thomas, 1995), and O2 (by photosynthesis);
2) contributing to the global warming by producing greenhouse gases like ammonia and methane (which would have a longer "life" due to the existence of the ozone layer);
3) climatic control;
4) stabilizing the planetary albedo;
5) creating biochemical cycles;
6) hydrological function (taking part in the water cycle on Mars);
7) producing biomass;
8) source of raw materials for the future colonists (food, fuel, building materials etc.).
The martian biosphere cannot and must not be identical to the terrestrial one. It would be the result of human intervention and must respond to human needs.
A. Preparing organisms for colonization
The first stage is the selection of candidate organisms. Their prelevation must be done from the terrestrial environments that are the most similar to the martian environment. For example, in the first phases of terraformation, the candidate species should resist to very low temperatures, to extreme dryness and to strong ultraviolet radiations. The conditions in the martian equatorial territorries would resemble those from antarctic deserts (Ross Desert) or certain arctic regions (Devon Island). This is where the necessary life forms should be searched. They would certainly be psychrophilic (cold-loving) bacteria, cyanobacteria and algae. According to their position in the biochemical cycles, these pioneer-organisms would be aututrophic, capable of feeding in the absence of organic substances, and, preferably, photoautotrophic, in order to enrich the martian atmosphere in oxygen.
Still, life conditions on Mars cannot be identical to those from any region of Earth. That is why a second stage is necessary, that of testing the candidate organisms in martian environments, simulated in the laboratory. Knowing and exactly reproducing the regolith composition, the atmospheric pressure and composition, the radiations, illumination, temperature and humidity is required. Studying the orgamisms’ behavior in these conditions will show if they are apt for colonizing Mars.
These life forms would have to adapt to very different situations from those in their natural environment. In many cases, they would need to suffer certain modifications. These could be realised either by genetic engineering, either by directed natural selection. Both solutions have their advantages and disadvantages.
Genetic engineering is a quick way of improving the physiological tolerances of an organism. Furthermore, it is not difficult for microorganisms, because these (especially prokaryotes) have a simple genetic material, relatively easy to decipher and modify. Also, they have accesory genetic material (plasmides) that can freely circulate within a microbial colony, through conjugation, and their information can be incorporated into the bacterial chromosome. For superior organisms, genetical engineering is more difficult. The main disadvantage of this method is that its effects cannot be exactly controlled. Inserting new genes in an organism’s DNA can cause methabolic problems that would make it unusable for terraformation.
Natural selection means the gradual changing of life conditions for a colony of candidate organisms. The individuals that survive to these changes would produce more and more resistant generations. Finally colonies adapted to martian conditions would be obtained. This method is slower and it is efficient only for organisms with a high reproduction rate and with a quite high genetic variability. Furthermore, it can be totally inefficient for certain species. This refers to organisms resistant to environmental factors that affect the genetic material (for example, to radiations). These, in order to keep their genetic information unaltered, have developed efficient DNA repairing systems that prevent mutations. But mutations are the premise of evolution. So, in many cases, resistance to extreme conditions can mean a low capacity to evolve.
The most efficient way of modifying the candidate organisms would be by combining genetic engineering with directional natural selection. Hiscox schematized the process of preparing terrestrial organisms for colonization:
Organisms ready for colonization should be grown to form sufficiently large colonies and, then, sent to Mars and released in suitable locations. Choosing and knowing the exact locations where these life forms should be implanted is extremely important.
The ecosystems created on Mars must be permanently supervised by human, their behavior influencing the colonization plan. The introduction of life on the planet must be realised gradually, according to a colonization plan. In order to conceive this plan, it is necessary to know and to understand the great biogeochemical cycles, the relationships between various species and between these and their environment.
B. Bacteria and algae
The first objective that must be achieved by terraformation is modifying the atmospheric composition by increasing the oxygen percentage, which would allow more and more complex organisms to grow. This can be realised by photosynthesis. If, on Earth, the way from anaerobiosis to aerobiosis took billions of years, on Mars, it is estimated that it would take between 21,000 and 100,000 years (McKay et al.).
Another priority is to create a natural nitrogen cycle, in order to supply organisms with the nitrogen they need, but also to release in the atmosphere a sufficient amount of buffer-gas. Other important objectives are to increase the atmospheric pressure and to accelerate the greenhouse effect (by releasing CO2, NH3, CH4), but also to produce biomass and to begin the pedogenesis (soil formation).
All of these would be realised by microorganisms like bacteria, cyanobacteria and microscopic algae, because these can colonize abiotic environments such as Mars. Due to their low nutritive requirements and high reproduction rate, they would quickly populate all the regions with suitable conditions.
The first colonizer organisms would have to resist to extremely low temperatures, to dryness, to radiations (until the ozone layer would become sufficiently thick), to low intracellular pH (due to CO2), to peroxides and other oxidizing factors in the regolith. They should have high osmotic tolerance, minimal nutritive requirements and they should be photosynthetic or anaerobiotic. They could be sent to the planet’s equatorial regions as soon as the temperatures would increase enough. The most suitable areas would be the former evaporation basins (rich in nitrates and carbonates), with low altitudes (here the humidity would be higher).
Three species are the most suitable for those conditions. These pioneer-organisms are described below.
Deinococcus radiodurans – is, probably, the most resistant terrestrial organisms. This bacterium was found in various environments, from altered meat to the cooling water of nuclear reactors. It is a polyextremophilic life form, resisting to extreme temperatures, to dryness, to oxidizing agents and, its most remarcable feature, to very high ultraviolet and ionizing radiation doses (due to its multilayered cell wall, carotenoid pigments and DNA repairing system). It is heterotrophic, anaerobic and can be useful by producing biomass (perhaps, from organic material from the planet’s natural satellites). However, its main importance is the genetical one, because the genes that give its resistance to radiations could be transferred to photoautotrophic organisms (Hiscox, 1995).
Chroococcidiopsis sp. – This cyanobacterium, studied by professor Imre Friedmann, is adapted to aridity and to large temperature variations. It is found from Antarctica to tropical deserts. It defends itself from the strong ultraviolet radiations by living under small translucent pebbles (it is endolithic). When life conditions become more favourable, it easily gives up the territory to more advanced organisms. It is photoautotrophic, producing oxygen.
Matteia sp. – is a filamentous, desiccation resistant, cyanobacterium. It is photoautotrophic. It can fixate atmospheric nitrogen when this element is absent in the enviroment. More important, it dissolves carbonates, releasing carbon dioxide and accelerating the greenhouse effect. (Friedmann, 1993).
Of course, long before these pioneer-organisms could colonize the planet’s surface, life could grow in biological enclaves, isolated from the unfavourable environment. As shown above, thermal waters could be directed to depressions in the crust, forming lakes. the ideal location for such lakes would be in the equatorial regions of the northern hemisphere, close to the demarcation line, in areas rich in nitrates and carbonates. Although, most of the time, these lakes would be covered by ice crusts, beneath the ice, temperatures ould grow towards the "spring". In such artificial lakes a great variety of cyanobacteria and algae could grow. Then, the global warming would melt the ice and would inundate the areas close to the demarcation line, creating large water basins where the algal populations would quickly expand.
During the first stages, artificial photosynthesis could also be used. The first "artificial leaf" was built by the American researcher Joseph Katz, following a simple scheme:
This produced a weak electric current and could release H2 from water. Later, more complex versions were able to synthesize organic substances and O2. However, the randament of such devices is very low. If more efficient instalations could be built, they could be sent to Mars, where they would contribute to the molecular oxygen production, during the early stages of terraformation.
The possibility of a natural O2 production should be also considered. Chemical analyses of the martian regolith show that water reacts with the oxides and peroxides in the upper layers, producing oxygen. When, due to the greenhouse effect, liquid water would inundate some areas of the planet, O2 would be released in the atmosphere.
Photosynthesis and carbon cycle
The most important biogeochemical cycle is that of carbon. Here is a simplified scheme of how it works, on Earth:
On our planet, gaseous CO2 represents a very small part of the atmospheric composition. On Mars, it forms and it will form most of the atmosphere. It is here that the carbon cycle must start. How would it look like? In the first stages of terraformation, human activity and the presence of a phytophagous fauna are, obviously, excluded. The formation of hydrocarbon and carbonate deposits takes place during long geological eras (anyway, recirculating carbon from limestone poses a great problem due to the lack of tectonic activity).
Here is the scheme of such a cycle:
The dominant biochemical process would be photosynthesis, by which atmospheric carbon would be fixed into organic substances and oxygen would be released.
There are two types of photosynthesis: oxygenic (uses water as an electron donator and produces oxygen) and anoxygenic (does not produce oxygen). Anoxygenic photosynthesis is realised, especially, by sulphur bacteria and will be discussed together with the sulphur cycle. The most important is the oxygenic photosynthesis, characteristic to some bacterial groups, like the Cyanobacteriales, the Prochlorophytes (a very small group of tropical aquatic bacteria that can sometimes use H2S instead of water) or the Halobacterium genus, to plants and to the vast and heterogeneous group of organisms, generally called "algae".
Photosynthesis can take place in extreme conditions. In the Ross Desert, in Antarctica, a rich endolithic flora, consisting of cyanobacteria, algae, lichens, yeasts and heterotrophic bacteria, was discovered. Some of these organisms can photosynthesise at 263 K (-10ºC). The main limitative factor is humidity. Endolithic lichens begin photosynthesis at 281 K, but they need a humidity of 70% around their body, and cyanobacteria need a humidity of 90%. Of course, genetic engineering could be used to increase their tolerance to dryness. Also, genetic engineering could increase the efficiency of photosynthesis, thus increasing the speed of the terraformation process.
Examples of such organisms are species of the genera Hemichloris, Gloeocapsa, Hormathonema, Chroococcidiopsis, Dunaliella, Chlamydomonas, Anabaena. Most of them are cyanobacteria. These life forms, although primitive, are the most suitable for colonizing Mars. They have simple nutritive requirements, they can resist for a long time in unfavourable life conditions, they reproduce fast, their photosynthetic randament is very high, they can use light with various wavelengths (400-700 nm), they contain lots of proteins. As shown above, some cyanobacteria, as well as some green algae, can grow in a pure CO2 atmosphere. Many of them fix atmospheric dinitrogen and some dissolve carbonates, releasing CO2. For a long time, cyanobacteria should represent the basis of the martian microbiota.
The first organisms, desiccation resistant cyanobacteria, such as Chroococcidiopsis sp. or Matteia sp., should be introduced in lowlands near the equator, where moisture would accumulate. The great canyon system Valles Marineris, very deep and, probably, rich in nitrate and carbonate deposits, would be an ideal location. At the beginning, cyanobacteria would grow endolithically, in order to protect themselves against radiations and to concentrate moisture. Then, after the formation of a sufficiently thick ozone layer, they would be able to expand on large areas. Friedmann proposed their "cultivation" under translucent plates (made of glass or of plastic material).
The global warming, the melting of the ice reserves, the formation of the first water pools in the equatorial zone and the increase of the atmospheric humidity would favour the implantation of new photosynthetic organisms. Also, the already existing cyanobacterial colonies would accumulate extra moisture, allowing the growth of species that are less resistant to dryness. In the first water pools, organisms from Antarctic lakes should be introduced.
Not only cyanobacteria, but also microscopic algae should be colonized. These have a high photosynthetic randament (80% of the oxygen in the terrestrial atmosphere is produced by algae). Species of Chlorella, Chlamydomonas, Scenedesmus would live together with the cyanobacteria.
The colonies of photoautotrophic organisms would produce the organic substances needed by heterotrophic life forms, of which the most important are the denitrifying bacteria. The increase of the amount of oxygen in the atmosphere would allow the introduction of new species. The existance of thermal springs (natural or artificial) woul offer optimal conditions for cyanobacteria and algae adapted to higher temperatures (for example, Cyanidium caldarium). Also, the implantation of some cyanobacteria capable of eroding rocks, such as Gloeocapsa sp., would represent the first phase of pedogenesis. When the temperature on Mars would be high enough, shallow seas, lakes and rivers would appear, these being ideal environments for algae. On land, vast territories would be covered by microscopic algae (especially in the moist regions).
Bacteria in the Halobacterium genus realise oxigenic photosynthesis, but they use organic carbon sources. They live in very salty environments. Species of the Chlorobacteriaceae family use organic carbon sources and CO2. They do not produce O2, but water (they could be a source of moisture for other organisms). The organic substance needed can come from cyanobacteria and algae or from the planet’s natural satellites (as shown in the previous chapters).
The problem of methanogenesis is also linked to the carbon cycle. Some archaea (Methanobacterium thermoautotrophicum, Methanococcus sp., Methanosarcina sp., Methanospirillum sp.) produce methane from CO2 and H2. Others use CO (present, in small amounts, in the martian atmosphere) and water, an organic substance (acetate, methanol) and H2, methylamine and methanol, or can decompose organic acids:
Usually, methanobacteria are aquatic (marine or continental) and live at various temperatures (15-100ºC). Still, most of them are thermophiles and could grow near thermal springs, producing methane, as a greenhouse gas. It must be said that scientists were able to grow some methanobacteria in the laboratory, in conditions similar to those on Mars. Methane is photolised by ultraviolet radiations, forming CO2.
A priority for the terraformation process is the creation of a nitrogen cycle on Mars. This two objectives. One of them is the formation of a sufficient quantity of atmospheric dinitrogen. The increase of the oxygen percentage, due to photosynthesis, would make the existence of a buffer-gas necessary. A buffer gas must be relatively chemically inert. It does not participate to the respiratory changes, but it temperates the oxidizing power of the atmosphere. Without it, any life form would simply burn. The most suitable buffer-gas is N2. The second objective is the circulation of this chemical element on the entire planet. Otherwise, life on Mars would be limited to the regions with significant nitrate reserves.
Here is a scheme of the nitrogen cycle on Earth:
For dinitrogen fixation (by bacteria and cyanobacteria) its partial pressure must be at least 5 mbar, while on Mars, it is only 0,3 mbar.
As shown in the previous chapters, it could be possible to release ammonia in the martian atmosphere, from subterranean reserves or "imported" from other regions of the Solar System. Ammonia is photolised, in the upper layers of the atmosphere, by ultraviolet radiations:
This way dinitrogen is naturally produced (due to the low gravity and to its low molecular mass, H2 would be lost in space). Ammonia’s lifespan would vary between 10 and 40 years, increasing after the formation of the ozone layer. Yet, the amount of NH3 that could be released in the martian atmosphere is unknown.
Therefore, the martian nitrogen cycle should begin with the nitrate depostis on the planet’s surface.
The first stage would be the denitrification (nitrate reduction). This is an anaerobic process realised by bacteria. It has two types: assimilatory and dissasimilatory. Disassimilatory nitrate reduction takes place according to the following simplified chemical reaction:
It can be noticed the production of oxygen (and water) by this process. Ammonia (under the form of the NH4+ ion) is released in the environment (soil), from where it is taken by other organisms and used for protein synthesis. Assimilatory denitrification is realised by species of the genera Aeromonas, Agrobacterium, Escherichia (this bacterium’s endospores resist to extremely low temperatures), Pseudomonas, Anabaena (this cyanobacterium is photosynthetic and very resistant to cold).
Disassimilatory denitrification consists of reducing the NO3- ion to NO2-, N2O, NO and, especially N2. It is characteristic for bacteria like Pseudomonas denitrificans, Alcaligenes sp., Achlobacter sp., Thiobacillus denitrificans, Rhodopseudomonas sphaeroides. These bacteria are heterotrophic and, for growing, they need organic substances (carbohydrates) produced by autotrophic organisms.
On Earth, denitrifying bacteria live in soil, especially around water. On Mars, they should be introduced together with the first cyanobacteria and algae, forming mixed colonies. The microorganisms that realise assimilatory denitrification would supply the entire colony with ammonium and would produce oxygen, the phototrophic ones would produce carbohydrates for the colony and oxygen, and the ones that realise disassimilatory denitrification would release dinitrogen. Denitrification should be very intense until the oxygen percentage would be high enough to force the denitrifiyng bacteria to retreat to anaerobic niches.
When the dinitrogen’s pressure would exceed a certain limit (around 5 mbar), its fixation would become possible. Nitrogen fixation means the transformation of N2 in NH4+ (rarely NO3-). This can be done abiotically (by combustion, vulcanism, lightnings etc.), but especially by bacteria and cyanobacteria. The process is anaerobic (oxygen inhibits the nitrogenase enzyme). There are various organisms that fix nitrogen. Many of them are more or less anaerobic: Clostridium pastorianum, Desulfovibrio sp., Desulfomaculum sp., Methanobacillus sp. (it is also methanogene), Klebsiella sp., Bacillus sp., Rhodoferax antarcticus (it is photosynthetic, anoxygenic and lives at low temperatures). Other nitrogen fixing bacteria are aerobic: Azotobacter sp., Derxia sp., Beijerinckia sp., Methylococcus sp., Azomonas sp., Spirillum sp., Rhodospirillum sp. (photosynthetic). Very active in this domain are cyanobacteria, especially the colonial ones. Although aerobic, they fix nitrogen in heterocysts. Heterocysts are special cells, different from the others in the colony, they are larger and have a thick cell wall that isolates them from the oxygen’s action, creating a suitable environment for nitrogen fixation. Examples of such organisms are species of the genera Anabaena, Chlorogloea, Lyngbia, Oscillatoria, Gloeocapsa, Nostoc, Cylindrospermum, Matteia. Once again, it can be noticed the importance of cyanobacteria for terraformation, due to the many functions that they could have in the martian environment.
Nitrogen fixing organisms can live freely, but also in symbiosis with some fungi (forming lichens) or with superior plants (some ferns, the Fabaceae, and the gymnospermes in the Cycas genus).
The next chemical process is nitrification. It is done by bacteria in soil and water. First, nitritebacteria (Nitrosomonas sp., Nitrococcus sp.) transform the NH4+ ion in NO2-, in the presence of O2 and CO2, forming nitrites. Then, nitratebacteria (such as Nitrobacter) transform the NO2- ion in NO3- (also, in presence of O2 and CO2). And the cycle goes on.
Both nitrates and ammonium salts are taken from the environment (soil, water) by plants, algae, cyanobacteria, that introduce them in the trophic chains. By excretion and decomposition, nitrogen returns to the environment, as ammonium ions (a process called ammonification). Also some bacteria can release gaseous ammonia in the atmosphere, contributing to the greenhouse effect.
The carbon, oxygen and nitrogen circulation can be reunited in the following scheme (Thomas, 1995):
The continuous line means matter transfer and the discontinuous line means energy transfer.
On Earth, the circulation of sulphur compounds plays a relatively small role. On Mars, where this element is much more abundant, it would constitute a basis for many life forms.
In nature sulphur is found, mainly, under three forms: compounds of the sulphate ion (SO42-), compounds of the sulphide ion (S2-) and molecular sulphur (S0).
It is known that sulphates, such as jarosite, are very abundant in the rocks at Mars’s surface. Also, on Mars there are many volcanoes. Most of them are inactive, but, recently, some clues of a present volcanic activity were found. On Earth volcanic activity is frequently associated with hydrogen sulphide (H2S) and methane emissions, with molecular sulphur deposits and with subterranean thermal waters. Probably, there should be the same situation on Mars.
The sulphur cycle should start with the huge sulphate reserves. Part of them would be used by various autotrophic and heterotrophic organisms (sulphur is one of the vital chemical elements). Another part would be reduced by sulphate-reducing bacteria, like Desulfovibrio sp. (that also fixates dinitrogen):
This biochemical process would form sulphydric acid and sulphides. The disassimilatory reduction of sulphates needs, as seen above, organic substances (ethanol, lactate, malate). These can be produced by heterotrophic microorganisms. Also, there are some aquatic archaea that produce H2S.
H2S is a gaseous substance that would be released in the atmosphere and would circulate on the entire planet. It is also a buffer-gas, between certain limits (in large quantities it is toxic).
The S2- ion in H2S or in sulphides would be taken by other microorganisms, that could use it in two ways: either for producing sulphates, either for producing molecular sulphur. Bacteria like Thiobacillus tioparus and Thiobacillus ferrooxidans oxidize S2- to SO42-, in aerobic conditions. Beggiatoa sp. produces molecular sulphur, also in aerobic conditions:
There are microorganisms that oxidize H2S anaerobically, by photosynthesis (the Thiorhodaceae and Athiorhodaceae families and, facultatively, the Prochlorophytes group). The purple sulphur bacteria (Thiorhodaceae) produce sulphates
The green sulphur bacteria produce S0:
These photoautotrophic organisms would produce biomass, would consume CO2 and would be the basis for some trophic chains.
Then, molecular sulphur can be oxidized, aerobically, to sulphates, by bacteria like Thiobacillus thiooxidans, Thiobacillus denitrificans, Thiomicrospora sp. or Sulfolobus sp. More important are species like Thiobacillus denitrificans, that couple sulphur oxidation with nitrate reduction, producing atmospheric dinitrogen:
On Earth, in some isolated areas, there are entire ecosystems based on sulphur compounds metabolization. On Mars, such ecosystems could become widespread, especially in the volcanic regions.
Life forms based on iron compounds metabolism
As shown in the previous chapters, iron is another abundant element in the martian lithosphere. The minerals at the planet’s surface contain, mostly, ferric compounds (with the Fe3+ ion).
There are certain bacterial species (such as Schewanella alga) that grow in the ferric compound deposits and reduce Fe3+ to Fe2+. Some of these can reduce haematite, releasing O2. This process, in addition to photosynthesis, would further increase the oxygen percentage in the atmosphere. Iron reduction takes place by using some organic substances. That is why these bacteria should live together with cyanobacterial and algal colonies.
In a more advanced stage, the Fe2+ ion can be oxidized to Fe3+ (in presence of O2, H2O and CO2 or of CO32-, HCO3- ions) by bacteria like Gallionella ferruginea, Thiobacillus ferrooxidans, Ferrobacillus sp., Acidithiobacillus ferrooxidans etc.
Many other transitional metals can be reduced and oxidized, the same way as iron.
Phosphorus circulates in the biosphere under the form of phosphates. The scheme of this cycle is very simple and its realisation on Mars poses no problems:
There are other biochemical cycles, of secondary importance, based on the production and metabolization of molecular hydrogen (H2), of carbon monoxide (CO) etc. All of them have as a result the production of biomass and energy.
C. Superior organisms
In the first stages of terraformation, the martian biosphere would be dominated by microorganisms (unicellular or colonial). Their role would be that of growing on large areas of the planet and of bringing the atmospheric composition to one similar to the terrestrial one, by increasing the N2 and O2 quantities and by decreasing the CO2 percentage. In the mean time, the global warming process would continue, temperatures on Mars beginning to resemble those on Earth. A rich hydrographic network would appear, formed of seas, lakes, rivers, and even a small ocean in the northern hemisphere. Water vapor would accumulate in the atmosphere (due to evaporation in the warm zones of the planet), forming clouds and precipitations.
In these conditions, the introduction of superior, pluricellular organisms should begin. Because the main objective is the intensification of photosynthesis, the process should begin with photoautotrophic life forms: lichens, mosses, superior algae, plants.
Lichens are symbiotic associations between various species of fungi (ascomycetes or basidiomycetes) and unicellular green algae or cyanobacteria. They are photosynthetic, they are much more resistant and use much more efficiently the environmental resources than unicellular algae that live alone.
Theoretically, some lichen species could be colonized even in the first stages of terraformation. There are, in Antarctica, endolithic lichens that can grow at extremely low temperatures (281 and even 249 K). They can hibernate for a long time at temperatures as low as 173 K. They need very low atmospheric N2 quantities and almost no O2. Of course, lichens need, usually, a relatively high humidity, but they can accumulate water reserves for resisting in arid conditions. Genetic engineering could be used to increase their resistance to desiccation.
Yet, lichens grow very slowly (maybe genetic modifications could be helpful in this case too), os that a quite long time should pass until they would cover large areas of the planet. Many lichen species could be introduced only when life conditions (especially temperature) would become more favourable. Due to their resistance, they could colonize more arid environments than cyanobacteria and algae.
Lichens have a huge importance for terraformation. They would populate vast territories, especially in the tropical regions. Their presence would accelerate the atmospheric transformation. The existence of vast green areas would reduce the planet’s albedo, contributing to the global warming. Also, many lichens can fixate atmospheric dinitrogen. With their rhizoids, lichens would fix the dust that cover the planet’s surface (reducing the damaging dust storms) and would erode rocks, triggering the pedogenetic process and preparing the terrain for plant colonization.
Mosses and first superior plants
Because the main limitative factor to organism growth on Mars would be temperature, the best model for the colonizing order of various species is the sequence of the vegetation zones on Earth. On our planet, there is a double sequencing of climate and vegetation, caused by latitude and altitude. The first vegetation zone is the tundra. Tundra is formed mostly by lichens, mosses and herbaceous plants.
Bryophytes (mosses) are small photosynthetic organisms, with quite simple physiological requirements. They can grow and photosynthesize at low temperatures. They tolerate a high CO2 level. It was found that, in moss colonies, CO2 partial pressure is around 3,6 mbar, compared to the 0,36 mbar in the terrestrial atmosphere (Tarnawski et al., 1992). Some experiments shown that bryophytes can resist to CO2 partial pressures as high as 20 mbar (Tarnawski et al., 1992). The oxygen quantity needed is also small: below 30 mbar, that means 3% of the 210 mbar O2 partial pressure in our atmosphere (Aro et al., 1984). They can resist for years to severe dryness and, when humidity increases, they can restart their photosynthetic activity.
In a first phase, mosses should be colonized in warm wet areas, already populated by lichens. Then, they would spread on vast territories, forming tundras and peat bogs. It was estimated (Fogg, 1995) that if 50% of the planet’s surface was covered by peat bogs, in just 700 years 20 mbar O2 would be produced, that is the minimal value needed for introducing superior plants (Armstrong şi Gaynard, 1976).
Beside the photosynthetic role, mosses would also have other important functions. Their presence represents a new stage of pedogenesis. Practically, the sequential colonization by cyanobacteria, lichens and mosses transforms an abiotic terrain into a soil with organic substances, suitable for plants.
The existence of peat bogs on Mars would also solve another problem. As shown above, the natural oxidizing processes in the upper regolith are very strong. This would cause the reoxidation of many organic substances, forming CO2. It was proposed, as a solution, burying some of the organic material of biological origin, but no method was proposed for doing this. It is known that, in acidity conditions (on Mars, the presence of atmospheric CO2 would acidize water), mosses like Sphagnum sp. form peat, an inferior coal. By this process, part of the organic carbon is prevented from reoxidizing, reducing the atmospheric CO2 quantity. Also the soil containing peat isvery fertile for plants. Gradually, the development of the hydrosphere, vegetation and soil, would neutralize the oxidizing properties of the regolith.
There are some aquatic angiosperm species (marine or continental), most of them monocotiledonates, that could be introduced on Mars in the same time with mosses. They have underwater rhizomes. The rhizomes tolerate low O2 levels, being able to resist for months in anoxia (Crawford, 1992). These plants have aerenchim tissues by which O2 is transported to the rhizome and CO2 is transported from the rhizome to the leaves. Such organisms should be colonized in lakes and in the litoral areas of seas.
Fogg synthetized the qualities necessary to the first plants that would colonize Mars. They should tolerate low oxygen levels, have small dimensions (to prevent the formation of an anaerobic core), a high surface/volume rate (favours autooxygenation), not too deep roots (the oxygen level decreases with the depth), internal porousity, internal ventilation, resistant and diffuse epiderm, seeds with starch (germinate at low O2 levels), nitrate respiration (produces more energy than fermentation), translucent tissues (allow photosynthesis in depth). Of course, some of these properties are found in various species while others could be obtained by genetic engineering. It is possible that the photosynthetic efficiency (relatively low in plants) could be increased by genetic engineering.
However, the main aspect that must be considered in selecting the colonist plants is their pollination. This must not depend on insects or other animals (that would not exist on Mars at that moment). The first plants should be pollinated by wind, by water, or even better, they should be able to reproduce by autopollination, apomyxia or vegetative means.
The growth of plants (and other organisms) on Mars would be favoured by the low gravity, the colonized species being able to grow larger that on Earth.
Creating the vegetation zones on Mars
Once the atmospheric oxygen level would exceed 20 mbar, large scale introduction of plants could begin. The only aspect that must be considered is the reproduction, as shown above. First, Arctic species should be colonized. Examples of such species are Papaver arcticum – an autopollinating Arctic poppy (Kevan, 1972), Saxifraga flagellaris – it breeds both vegetatively and by apomyxia (Fryxell, 1957), Eriophorum sp. – anemophile. This way, the first true tundras would appear.
The next vegetation zones are those of temperate forests and steppes. Gradually, the global warming would make the tundras to migrate to higher and higher latitudes, making place for these new types of vegetation.
On Earth there are many anemophilic tree species (240 only in North America). Of the most common can be mentioned the spruce, the fir, the beech, the oak, the asp etc. These would form vast forests, in which mosses, ferns and herbaceous plants would also live. Forests would further reduce the CO2 percentage in the atmosphere, using it to produce biomass and releasing O2.
Temperate steppes should also be created on Mars, many steppe plants (especially the Poaceae) being anemophilic. Even the widespread dandelions can reproduce asexually. Plants with economical importance could be introduced. Tomatoes, peas (species that enriches soil in nitrate compounds, due to nitrogen fixation), lettuce, some sorts of potatoes, blackberries, raspberries and other comestible plants are autopollinating. Of course, they would grow in the wild environment, but, when the first colonists will arrive on Mars, they would cultivate and use these plants.
Finally, when temperatures on Mars would become similar to those on Earth, in the tropical regions new specific types of vegetation would appear. Probably, Mars would not have large rainforests (not enough humidity), but savannah and Mediterranean vegetation Zones could be created.
The situation is the same for the aquatic flora. First, cold climate macrophyte algae (many species of brown, red and green algae) would be colonized, and, then, temperate and warm climate species. The shallow seas and oceans would allow an explosive growth of these organisms.
Creating trophic chains and ecological balance
The next step is the introduction of animals. This needs an increase of the atmospheric O2 percentage, and, more important, a decrease of the CO2 level (at high concentrations, this gas is toxic to animals). First, more primitive animals, with simpler physiological requirements, should be colonized.
Many plant species are pollinated by insects (rarely by birds or bats). These plants could be colonized on Mars only together with the coresponding pollinator animals.
Animal life would be able to develop in seas, oceans and lakes. The small depth of the martian seas would allow their good illumination and oxygenation, and a great abundance of algae. Here, various genera of crustaceans, annelides and even fish should be colonized. These waters should be ideal for corals (at least in the tropical zones), that will contribute to the reduction of the atmospheric CO2 level, fixating it as CaCO3.
More and more complex organisms would populate the land. When the CO2 partial pressure would be below 10 mbar, that of N2 – above 300 mbar and of O2 – above 130 mbar (but not more than 300 mbar), humans and other superior terrestrial vertebrates would be able to live on Mars.
The introduction of phytophagous and carnivorous animals and the growth of decomposer organisms, would cause trophic chains to develop. Their creation must be carefully supervised by humans. The result would be a self-regulating martian biosphere. All the biochemical processes must balance each other, in order to maintain the life conditions needed by the human species. For example, the martian atmosphere, would always have to contain a small percent of CO2 (but higher than on Earth), as a greenhouse gas. That is why the aerobic biochemical processes (animal respiration, bacterial oxidation of ferrous compounds) would have to equilibrate, at one moment, the photosynthesis realised by plants. Otherwise, the CO2 quantity would decrease too much, and together with it, the temperatures on the planet, affecting the human population, and martian life, in general.
Creating trophic chains similar to those on Earth and self-regulating ecosystems would be a complex and difficult task. However, we already have the scientific knowledge necessary. Joe Hanson realised the first closed aquatic ecosystem. It contained algae, nitrifying bacteria and small crustaceans, that lived together in artificial water basins. The ammonia excreted by the crustaceans was transformed in nitrites and then in nitrates by bacteria. The nitrates were taken by algae, which were realising photosynthesis,were growing, reproducing and were eaten by the crustaceans. Since then, other artificial self-regulating microecosystems were created. Also, the capacity of various organisms to adapt to the new conditions they would find on Mars, must not be underestimated.
Any new trophic chain created on Mars would first have to be tested in a limited space, under careful supervision, and, then, let to develop by itself, on the entire available area.
D. Human colonization
The final purpose of the entire terraforming process is the population of planet Mars by humans. When the atmospheric, climatic and biological conditions would become favourable, the first colonists could move to Mars. The colonization would begin, probably, in the tropical regions, especially on the sea coasts. The first colonies would be, dominantly, agrarian, and, after a certain time, industrial activities could develop.
Gradually, Mars could become a home for billions of people.
E. Long term problems
The terraformation process would never be completely finished, the permanent supervision of life conditions being required. There are four main factors that man cannot control and that would affect, on a long term, the martian ecosphere.
Variations of the martian axis inclination
The inclination of our planet’s rotation axis varies over long periods of time. Such variations contributed, for example, to producing the Quaternary glaciations in Europe and North America. However, Earth’s natural satellite, the Moon, by its gravitational force, reduces the amplitude of these variations.
Unfortunately, Mars’s satellites are much too small to have such an influence. That is why the inclination of the planet’s axis can vary with tens of degrees. So, areas that are now located at the equator, in the future could move to the poles. This phenomenon would have a devastating effect on the martean life.
However, these variations take place over long periods of time, giving enough time to the various life forms (including the human population) to migrate to more suitable regions of the planet.
Lack of tectonic activity
Unlike the situation on Earth, the martian lithosphere is unitary. There are no tectonic plates, rifts os subduction zones. This prevents the efficient recirculation of the chemical substances in the lithosphere, mantle and atmosphere. Apparently, this contributed, in the past, to the loss of most of the planet’s atmosphere. For example, carbon (of biological origin or not) fixed, as carbonates or hydrocarbons, in sedimentary rocks, would "sink" into the crust, being unable to come again to the surface. The effects of this would be visible only after very long geological eras.
The solution that mankind will find to this problem cannot be anticipated. It would be possible the creation of biochemical cycles that would replace the geological ones.
The lack of a magnetosphere causes the martian atmosphere to be continuously eroded by ionized particles come from the Sun (the so-called "solar wind"). With the exception of some territories in the Southern hemisphere, where there is a stronger magnetic field, the planet is not protected against the solar wind. Over long periods of time, the erosion would affect most of the atmosphere, causing the loss in space of the composing gases and deteriorating the life conditions on Mars.
The solution would be to create an artificial magnetosphere. For this, building some huge orbital electromagnets or many smaller ones, placed on the planet’s surface, would be necessary.
This problem is a purely technical one and could be solved in a not so far future.
The gravitational force on Mars is three times weaker than the terrestrial one. Yet, it is sufficiently strong to not affect the living organisms and to prevent the loss of the various chemical substances, with one exception: molecular hydrogen. This is produced in some biological and chemical processes (such as the photolisis of NH3, of CH4 etc.) and its molecular mass is to small to be retained on the planet. This way, in a very long time, a large part of this important chemical element would be lost to space.
Some solutions were proposed, such as placing into orbit of small solid fragments (something like the "rings" around Jupiter, Saturn, Uranus and Neptune) which, due to their high revolution speed would atract, slow down and send back to Mars the H2 molecules.
There are also other problems, like the influence that the Moon and the terrestrial magnetosphere have on the behavior of some animal species (causing difficulties in their adaptation on Mars). Solutions will, probably be found in a far future, when mankind will posess other scientific and technical knowledge.
The terraformation of Mars would be a complex, difficult and long process, but it is absolutely necessary. It would last for tens or even hundreds of thousands of years. This essay analyses the problem by considering the actual technological and scientific level of the human species. Of course, in time, new technologies will appear, that could make the process easier and faster. In order to achieve this objective, a sustained effort of the governments, the international institutions, the scientists is required, as well as a long term planning.
The advantages that the colonization of a new planet would bring to humankind would be huge. The most obvious is the appearance of a debouchement for the demographic growth on Earth. However, maybe more important than the terraformation of Mars itself, it would help developing new technologies that would allow the terraformation of other celestial bodies. It is possible that, before the first people would colonize Mars, the ecopoiesis process would already be triggered on other planets. Considering the planet’s characteristics, it could be said that if mankind cannot colonize Mars, it will not be able to colonize any other planet of the Solar System.
The new planet would also be important from the economical point of view, by its huge iron reserves, by being located close to the mineral rich asteroid belt and by its agriculture (the low gravity would favour the growth of bigger plants).
The political factor must not be neglected. The realisation of this project would need a close cooperation between all the states of the world.
When should the preparations for terraforming begin? Considering the long duration of the process, right now. First, a very detailed analysis of the planet’s geochemical characteristics would be required.
The purpose of this essay is to show that terraformation is possible, even with the current technico-scientific means. All that is needed is the will to do it.
6. SELECTIVE BIBLIOGRAPHY
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G. Zarnea – Tratat de microbiologie generală (volumul II) – Editura Academiei R.S.R., Bucureşti, 1983
E.R. Solomon, L.R. Berg, D.W. Martin, C. Villee – Biology – Saunders College Publishing, 1993
Martyn J. Fogg – Terraforming Mars: A Review of Research – http://www.users.globalnet.co.uk/~mfogg/paper1.htm
Martyn J. Fogg – Pioneer Organisms Nominated for Terraforming – http://www.users.globalnet.co.uk/~mfogg/pioneer.htm
James M. Graham, Linda E. Graham – Physiological Ecology of Terrestrial Microbes on a Terraformed Mars –
James M. Graham, Linda E. Graham – Succesional Stages in Terraforming Mars –http://www.marssociety.org/content/proceedings1998/mar98090.htm
Charles R. Hancox – Terraformation of Mars –
Robert H. Haynes – How Might Mars Become a Home for Humans –
Julian A. Hiscox – Biology and Planetary Engineering of Mars –
Margarita Marinova, Katie Strong – Super Greenhouse Gases Analysis – http://www.users.globalnet.co.uk/~mfogg/marsfront.html
Richard W. Miller – An Ecological Approach to Terraforming. Mapping the Dream – http://www.marssociety.org/content/proceedings1998/mar98092.htm
Aubrey Weese – Proposed Methods for Terraforming Mars –
Patrick Wittome – Waterfield Reservoir Management –
Robert M. Zubrin, Christopher P. McKay – Technological Requirements for Terraforming Mars – http://www.users.globalnet.co.uk/~mfogg/zubrin.htm