Proposed Methods for Terraforming Mars

Aubrey Weese

School of Computational Sciences,
George Mason University, Fairfax VA

May 5, 2003

Terraforming is the process of transforming a hostile environment into one suitable for human life. Just by looking at Earth, it is apparent that humans are capable of altering the environment of an entire planet. Our introduction of greenhouse gases into the atmosphere has been sufficient to modify the climate. This has lead to suggestions that we should take measures to counteract the predicted warming - in effect 'terraforming' the earth. In the process of modifying mars, we are certain to learn much more about how planets really function and evolve. Perhaps through this process we will understand the principles of climatic variation on earth, and the correlation between the climate and the biosphere. This knowledge will contribute to wise management for our native planet, and ideas about how to reduce the global damage done by pollution and deforestation.

Certain things about a planet are unalterable, such as its orbit, rotation rate, mass and volatile inventory. The things that we can change include: the distribution of volatiles, the surface temperature and pressure, the atmospheric composition and opacity, planetary albedo, precipitation and humidity. The reason that mars has been chosen as a prime candidate for terraforming is that its unalterable characteristics are remarkably consistent with life. The alterable ones are not, but the assumption of terraforming is that we can change them to be so. Let us start by taking a look at some of the characteristics of mars today, compared with those on earth.

The surface gravity on mars is 0.38 times that of earth and the planet is 1.52 times as far from the sun, receiving 43% of the sunlight that earth receives. This amount is still much more than is needed for photosynthesis. The average surface temperature of earth is 15° C (58° F). Mars average temperature is -60° C (-80° F), with extremes that range from 23° C (75° F) to less than -73° C (-100° F).

The Martian day is 24 hours and 40 minutes, and the Martian year is 687 days long. The planet is still close enough to the sun to experience seasons. Since the year is longer, the seasons are longer. Summer in the northern hemisphere lasts 178 days with mars at perihelion (128.3 million miles from the sun) and winter lasts 154 days with mars at aphelion (154.8 million miles from the sun). The southern hemisphere has longer, harsher winters and shorter, cooler summers. The seasons may vary a bit more than earth's as well. Orbit eccentricity is .093 compared to Earth's .017, and axial tilt is 25.2 degrees compared to Earth's 23.4 degrees.

The volatiles in Mars atmosphere are listed in the chart below:

Species Abundance by Volume Partial Pressure

CO₂ 0.9532 7 mbar

N₂ 0.027 0.2 mbar

Ar 0.016 Minor

O₂ 0.0013 Minor

CO 0.0007 Minor

H₂O 0.0003 Minor

Ne 2.5 ppm very minor

Kr 0.3 ppm very minor

Xe 0.8 ppm very minor

O₃ 0.04 to 0.2 ppm extremely minor

(Hiscox)

Earth's atmosphere:

78.1% nitrogen
20.9% oxygen
0.9% argon
0.1% carbon dioxide and other gases

The total atmospheric pressure on mars varies from approximately 7.4 mbar to 10 mbar. The variance is caused by a seasonal difference in temperature. Higher temperature leads to higher pressure as gases evaporate. This principal underlies all terraforming schemes for mars because what is needed to make the planet habitable is both higher surface temperature and higher atmospheric pressure.

Now let us take a look at how we would need mars to be different, first to support plant life and then to support human habitation.

For plants:

Optimistic ideas have been put forth of adapting organisms to live in the Martian environment as it is currently, but if these creatures do or could exist, they would have metabolic rates that are too low to cause any noticeable changes in Mars environment. At present the Martian surface is effectively sterilizing for all forms of terrestrial organisms. The low temperature would completely freeze any organism. The formation of ice crystals could cause cellular damage and would make the transport of chemical substances inefficient. In addition the low temperature would raise the activation energy for enzyme catalyzed processes, inhibiting biochemical and metabolic reactions. The UV radiation on the surface also can be lethal because it is absorbed by nucleic acids (DNA) and activates the formation of substances that inhibit replication and transcription. This UV radiation also causes strong oxidants to form in the regolith on the Martian surface that are damaging to cellular components. The high carbon dioxide concentration would probably cause a low intracellular pH (acidosis) in organisms that can damage cellular proteins, cellular components, and metabolism (Hiscox).

The carbon dioxide pressure on earth is about 0.35 mbar. This is low enough that some plants are actually limited in their ability to obtain CO₂ for photosynthesis. However other plants can continue to photosynthesize at the same rate down to vanishingly small concentrations. In general, photosynthesis is depressed if concentrations descend below 0.25 mbar. So for mars, McKay et al have set an ideal CO₂ concentration of at least 0.15 mbar, and no greater than 1 mbar (1991). Concentrations greater than 1mbar can have adverse effects on some species, although Seback et al. found photosynthetic allege that could thrive in pure CO₂.

Plants actually prefer oxygen levels well below the current value on earth. Photosynthetic production increases as O₂ is reduced from its earthly 210 mbar down to around 20 mbar. At 20 mbar or lower metabolic complications ensue, because of a mitochondrial enzyme in plants that requires oxygen. However this enzyme has such an affinity for oxygen that plants may be able to be adapted to function at pressures as low as 0.1 mbar. At least one species of algae can survive with little or no oxygen. Seckback et al. successfully grew Cyanidium caldarium in an atmosphere of pure CO₂ (Thomas 1995). All organisms need nitrogen in enough quantity to allow for biological nitrogen fixation. Bacteria are able to accomplish this at concentrations of 10 mbar or less.

Plants and anaerobic microbes have been shown to be able to survive at total pressures well under 1 mbar. So, adding all these together, the total pressure of the atmosphere needs only to be high enough to support the vapor pressure of water at ambient temperatures (which would be 6.1 mbar at 0° C). Currently mars atmosphere does reach this pressure at the poles, but the temperature is too cold there, and at the equator, where the temperature does rise above 0° C in the summer, the pressure is not high enough for liquid water to form.

This is summarized in the table below

Component Limits Reason

Average Global Temperature At least 0° C Freezing point of water

Total Pressure > 10 mbar Water vapor pressure plus O₂, N₂ and CO₂

CO₂ > 0.15 mbar Photosynthesis

N₂ 1-10 mbar Nitrogen fixation

O₂ >1 mbar Plant respiration

On mars today, the mixing ratio of O₂ is 0.13%. If the pressure of CO₂ were raised to 2 bar (which is what would be needed to keep the temperature above freezing), the oxygen would raise to 2.5 mbar. This would be enough for plant respiration. Assuming that a few millibars of nitrogen could be released from the regolith by soil microorganisms, a habitable plant environment would then exist.

For humans:

Because of the difference in mass of Mars and Earth, Mars would require an atmosphere about three times as dense as that of earth to be breathable by humans. The minimum tolerable oxygen pressure for humans is 130 mbar. At concentrations too far above the current earthly level of 210 mbar, symptoms of oxygen toxicity began to appear, as well as problems with flammability of natural substances. For this reason, McKay et al. set the upper limit at 50% above the current level, or approximately 300 mbar (1991). In addition, to help prevent toxicity and flammability, a buffer gas is needed.

On earth this buffer gas is nitrogen. Elements that can possibly be used as buffer gases include helium, neon, nitrogen, argon, krypton and xenon. However the presence of all of these in the atmosphere of mars is negligible. More complex gases such as CH₄, H₂O, CO, HCN or SF₆ could also serve as buffers, but would most likely not be able to be made in sufficient enough quantities. Really the only candidate is nitrogen that might exist as nitrate in the Martian regolith. The total pressure of all the gases combined needs to be at least 500 mbar (this is determined by studies of people living at high elevations of 15,000 to 20,000 feet. The results are summarized in the table below.

Component Limit Reason

Total Pressure > 500 mbar High elevation studies

CO₂ < 10 mbar Set by toxicity

N₂ > 300 mbar Buffer gas

O₂ 130-300 mbar Hypoxia (lower limit), flammability (upper limit)

Studies have been done to determine what the environment of mars would be like if it had an atmosphere just like earth's. The surface temperature on the planet would be considerably warmer than it is now because the carbon dioxide content would be about 30 times greater. However, it would still be far too cold to be habitable.

Changing the Atmosphere of Mars

At first glance it may seem that we could import volatiles into the atmosphere of Mars to make it more like earth's. But a look at the scale that would be needed shows that this is implausible. The mass of gas needed to produce an atmospheric pressure of just 1 bar on Mars is approximately 4 x 10¹⁵ tons. Yet the Space Shuttle is capable of lifting only 40 tons into low earth orbit, and even proposed heavy lift launchers can only carry 140 tons. However, this should not pose a problem because scientists have predicted that we can find everything necessary for terraforming in the soil of mars. We will not know this for sure until further exploration has been done.

Many estimates have been done as to the total volatile inventory of CO₂, water, and nitrogen on mars. These estimates have varying results, but one thing they hold in common is that they are greater than the abundance of water, CO₂ and nitrogen currently in the Martian atmosphere. An addition, the present loss rate due to atmospheric escape to space is insufficient to deplete them to their current values. There is evidence that mars one possessed a more clement climate with liquid water on the surface and a dense carbon dioxide atmosphere. This past history provides hope that we might be able to return mars to its former state. However the pressing question that must be answered is: where did these volatiles that used to be in the atmosphere go?

The answer is either one of two things. (1) Most of the volatiles are now in subsurface reservoirs on the planet. (2) Mars lost a considerable portion of its early atmosphere due to high velocity impacts. Determining which of these is the case is crucial, for if the latter is the case, it is unlikely that terraforming would be possible.

We know that Mars has lost a some of its atmosphere due to erosion by solar wind. This wind carries a magnetic field that picks up ions from the upper atmosphere, accelerates them, and then smashes them back into other ions at several hundred kilometers per second, knocking ions out to space. If a planet has a magnetic field, like earth does, the field will shield the upper atmosphere from the solar wind. Earth has a molten iron core, and its magnetic field is created by the swift rotation of the planet swirling the liquid core. This field has a strength at the surface of 30,000 nanoTeslas. By comparison, mars has only a patchwork of localized fields with strengths on the order of 1500 nanoTeslas (Space Daily).

(Space Daily 2000)

This map shows the vertical component of the magnetic field originating from the Martian crust. The north pole is at the top. In the southern hemisphere around 180 degrees longitude you can see a banded pattern as the field switches polarity as you move from north to south. The Mars Global Surveyor, launched in 1996, has mapped the planet's ionosphere. These maps show that where localized surface magnetic fields are strong, the ionosphere reaches to a higher altitude, indicating the solar wind is being kept at bay. In a way, these fields act as umbrellas scattered over the planet protecting the atmosphere. Mars at one time probably had an inner dynamo like the earth that would have generated a global magnetic field. It is speculated that because the planet is small, it cooled rapidly, losing its inner dynamo about 4 billion years ago. This speculation arises from the fact that ancient asteroid or comet impacts wiped out the crustal magnetism. The craters they formed are 4 billion years old, and have not been subsequently remagnetized. Because of the loss of the global magnetic field, much of the formerly thick atmosphere of mars was eroded away.

The big question is: when this dynamo stopped, did most of the atmosphere escape to space because of the lack of the magnetic field; or, did most of it sink into the soil after volcanic activity stopping cycling it back into the atmosphere? If too much of the early atmosphere was lost too space, recreation of it will be a lot more difficult. If, however, most of it has been absorbed by the regolith and polar caps, the recreation is far simpler.

If large volatile reservoirs do exist on mars, they could take several forms. The polar caps may hold as much as 5,000 km of water, which would correspond to a layer 4 cm thick covering the entire planet. This would not be enough for a green planet, however much larger amounts may be tied up as permafrost in regions over 30° latitude. CO₂, in addition to possibly being stored in the south polar cap and the regolith, may also be stored as carbonate rocks. The carbonate rocks would have formed early in mars history by the reaction of CO₂ with silicate minerals in the presence of liquid water. There is some spectral evidence for this. Also, Warren (1987) estimates that the regolith's low Ca/Si ratio is due to the fact that Ca was removed as calcium carbonate. The layered deposits in the Valles Marineris are thought to be derived from the precipitation of 30 mbar of atmospheric CO₂ as carbonate in ancient Martian lakes (Nedell et al. 1987). However releasing the CO₂ from these rocks would be much more difficult than releasing it from the polar cap or the regolith.

Of all the major CHNOPS elements required for life, the two we have not discussed yet are sulfur and phosphorus. Sulfur has been reported at the Viking landing sites to be available on mars at concentrations 10 to 100 times those in terrestrial rocks and soils. Phosphorus was not measured by Viking because its x-ray fluorescence signal was masked by S and Si, but it is thought to be present. Most of the trace elements required, such as Fe, Mg and Al have also been directly detected. The most serious potential shortfall of material is N₂. Whether non-atmospheric reservoirs of this gas exist is probably the most critical question of all.

So, if we cannot import atmospheric volatiles, how are we going to get them out of the supposed surface reservoirs on mars, in order to do the work of terraforming the planet?

Runaway Greenhouse Effect

The most widely proposed solution is to warm the surface of the planet by a possible runaway greenhouse effect. It is assumed that there is a reservoir of frozen CO₂ on the south pole of mars. This cap is about 350 km in diameter. An initial warming would cause sublimation of this CO₂, which would further add to the warming and sublime more CO₂, creating a positive feedback loop. Initial estimates of the requirements for engineered warming of mars are reduced by about 2 orders of magnitude when this feedback is considered (Zubrin et al.). If the cap were 1 km thick, total sublimation could provide 100 mbar of CO₂ to the atmosphere. In addition there may be CO₂ absorbed in the Martian regolith that could provide an estimate of 300 mbar to the atmosphere. McKay et al. have calculated that if this CO₂ is concentrated in the regolith at the poles (a reasonable assumption because cold regions will preferentially collect it), and if the temperature increase needed to outgas it is 25K, mars could switch to a new stable state with a surface pressure of about 800 mbar and a surface temperature of 250 K. If the total reservoir is 2 bar, the steady state temperature would increase to 273K, and if it is 3 bar, it would increase to 280K (1991).

This entire process can be mathematically modeled in the following way:

McKay and Davis give a function for estimating the mean temperature on Mars as a function of CO₂ atmospheric pressure and the solar constant (1991).

where T_mean is the average planetary temperature in Kelvins, S is the solar constant (which for the present day sun equals one), T_BB is the black body temperature of Mars at present (213.5 K), and P is the CO₂ pressure given in bars. This equation can be modified to find the temperature at any latitude by taking the following steps:

Considering that the atmosphere transfers heat from the equator to the pole, we can say

where DT is what the temperature difference between T_mean and T_pole would be if there was no atmosphere (about 75 K). Based upon rough approximation and observed data we can further say that T_max = T_equator = 1.1T_mean and that the global temperature distribution is given by T(q) = T_max - (T_max - T_pole)^sin(1.5q), where q is the latitude. The interaction between the reservoirs of CO₂ in the polar cap at the Martian atmosphere is well understood, and is simply a function of the vapor pressure for CO₂ and the temperature at the poles. This CO₂ vapor pressure curve is approximated by

Zubrin and McKay used these equations to plot the vapor pressure vs temperature for mars. Wherever the vapor curve crosses the temperature curve, we have equilibrium. This happens at points A and B on the graph above. A is a stable equilibrium and B is an unstable equilibrium. Where the temperature curve lies above the vapor pressure curve, the system will move to the right, towards increased temperature and pressure, in a runaway greenhouse effect. Where the temperature curve lies below the vapor pressure curve, the system will move to the left in a runaway icebox effect. Mars today is at point A, with 6 mbar pressure and 147K temperature at the pole.

The interesting thing to consider is what would happen if the temperature was artificially increased by several degrees K. The temperature curve would shift upwards, causing points A and B to migrate closer together. An increase of only 4 K would cause the curve to move up far enough that it would be above the vapor pressure curve everywhere on the graph. The result would be a runaway greenhouse effect that would cause the entire pole to evaporate. Once point B is surpassed, the runaway greenhouse condition will maintain itself without further artificial heating.

If the temperature should rise to such a point that the cap completely evaporates, the atmosphere will begin to regulated by the CO₂ in the Martian regolith instead. The relationship between this soil reservoir, the atmosphere and the temperature has been estimated in parametric form by the equation

where M_a is the amount of gas adsorbed in bars, g = 0.275, C is a normalization constant used to make the equation reflect known Martian conditions, and T_dis the temperature increase needed to release gas from the soil. The equation is a variation of Van Hofft's law for the change in chemical equilibrium with temperature. So, there is fair confidence that the general form is correct; however the value of T_d is unknown and most likely will remain so until there is human exploration of mars. The lower the value turns out to be, the easier things will be for prospective terraformers.

Zubrin and McKay used the global temperature distribution given in above to integrate this equation over the surface of the entire planet. The chart below shows what the regolith pressure-temperature equilibrium points would be for T_d values of 20, 25 and 30 K.

This graph assumes a total planetary volatile inventory of 500 mbar CO₂. For the normal regolith temperature (thick line), if T_d = 20, enough CO₂ will be outgassed from the regolith to produce a final Martian atmosphere of 300 mbar. But if T_d = 25 or 30, the value declines to only 31 or 16 mbar. This dramatic dependence on the unknown T_d value is unsettling. However, if the temperature of the planet was artificially raised 10K above what would be produced by CO₂ outgassing alone (thin line), the results are much different. Now the T_d convergences move close together towards a final atmosphere of several hundred mbar. This shows that the final conditions of the atmosphere regolith system on a terraformed mars are controllable.

But how is the artificial portion of the warming to be accomplished?

The three solutions that have been put forward are

Orbital Mirrors
Production of CFCs
Importation of ammonia rich objects

I will discuss each in turn, though most likely the best approach will be a synergistic method that combines all of them.

Orbital Mirrors:

NASA is currently working on a solar sail propulsion system that uses large reflective mirrors to harness the sun's radiation to propel spacecraft. Another use of these kind of mirrors could be place one of them a couple hundred thousand miles away from mars and use it to reflect sunlight back onto the surface. Scientists have proposed an aluminized mylar mirror that would have a diameter of 250 km (155.34 miles), covering an area larger than Lake Michigan. It would reflect enough sunlight to raise the entire area south of 70 degrees latitude by 5 K. The mirror would weigh about 200,000 tons, which means it would be far too large to launch from Earth. However, there is the possibility that the mirror could be constructed from material found in space, possibly from asteroids or Martian moons. This mirror would not have to orbit the planet, but instead could hover "statite" at an altitude of about 214,000 km as the gravity of mars balanced the light pressure from the sun.

(Zubrin et al.)

This mirror could later be used for other purposes on mars. Were it to concentrate its power on a smaller region, it could melt the Martian permafrost or volatilize nitrate beds. Thus, while this mirror would require a large amount of engineering effort to create, the benefits to terraforming of being able to wield tens of TW of power in a controllable way are immense. The material required to create such a mirror is equivalent to just five days worth of Earth's production of aluminum. And, a space mirror has already been tested in earth orbit by the Russians, who used a 20 m mirror to heat Znamia (Fogg).

Production of CFCs:

Another proposed solution is to add clouroflorocarbons (CFC's) to the atmosphere. These are super greenhouses gases that absorb in the radiation window where CO₂ and H₂O have little absorption (between 800 and 1,200 cm-1). Gases of particular interest are CF₃Br, CF₆, CF₃Cl and CF₂Cl₂. These gases could be made of elements found on mars, and they have long lifetimes against destruction by solar radiation. The gases would be needed in concentrations of parts per million or more in order to produce the required warming of about 60° C.

The drawback to CFC's is that they would have the effect of destroying any ozone layer on mars, just as they can destroy the ozone layer on earth. If there is no ozone layer, the gases themselves will be photolyzed by ultraviolet light of wavelength 200-300 nm, which breaks the C-Cl bond. For example, carbon tetraflouride has a half life of thousands of years on earth, but on mars with no ozone layer it has a half life of only thirty hours. Taking this into account, about 3 x 10¹² tons of CFC's would have to be produced every year to offset the loss. The gases themselves would shield the surface from ultraviolet radiation. Current earthly production of CF₃Cl and CF₂Cl₂ is around 106 tons per year.

Alternative greenhouse agents such as perflurocarbons have been suggested because the C-F bond is much more robust. But, their toxicity at the concentrations required for warming mars have not been determined, and neither have their relevant absorption bands.

Importation of ammonia rich objects:

Another greenhouse gas is ammonia (NH₃). This gas, along with methane (CH₄), is less powerful than halocarbons but more powerful than carbon dioxide. Ammonia rich asteroids could be diverted from the outer solar system towards the Martian atmosphere. This would actually be easier than diverting an asteroid from the Main Belt within the solar system, because the father away an object is from the sun, the slower its orbit. Therefore the velocity change needed to distort that orbit smaller, and the gravity from other planets in the solar system can assist in deflecting the velocity as well.

For this to be done, nuclear thermal rocket engines would have to be somehow attached to asteroids from the outer solar system. The rockets would move the asteroids at about 4 kilometers per second, for a period of about 10 years, before the rockets would shut off and allow the 10-billion-ton asteroids to glide, unpowered, toward Mars. If it is possible to smash an asteroid of such enormous size into Mars, the energy of one impact would be enough to melt about a trillion tons of water. That is enough water to form a lake, with a depth of one meter, that could cover an area larger than the state of Connecticut. Enough ammonia would be released to raise the Martian temperature by 3° C and to form a shield against UV radiation.

If one of these asteroids was smashed into mars per year, within 50 years we could create a temperate climate and enough water to cover 25 percent of the planet's surface. However, the bombardment by asteroids, each releasing energy equivalent to 70,000 one-megaton hydrogen bombs, would delay human settlement of the planet for centuries.

It would require more than one million comets of 1km radius to provide the mass equivalent of 1 bar atmosphere on mars. Also the composition of any such asteroid is unlikely to contain more than 10% NH₃. Furthermore, the lifetime of the gas is estimated to be only 10 to 40 years. Therefore ammonia objects would continue needing to be imported, although at a reduced rate. Or, biology might be able to take over this role by producing ammonia or methane.

How long, in total, might all of this take?

Timescale

The energy required to sublime 2 bars of CO₂, warm a layer of Martian regolith 10 m thick, melt a layer of water 10 m thick and evaporate water into the atmosphere is approximately 10⁶ J/cm², which is equivalent to 10 years of mars solar energy. If the process could be sustained and could use 10% of the solar energy on mars it would take about 100 years. However, if you consider the depth of CO₂ and ice to extend down to 500 m, these time scales are enlarged to 10⁵ years, accounting for the rate of diffusion of heat into the regolith.

The time required to produce an oxygen rich atmosphere via photosynthesis is over 100,000 years. This estimate is based on biological energy efficiency in terrestrial ecosystems, which averages 10^-4. Specially designed organisms could yield much higher efficiencies. McKay et al. note that the limiting factor may not so much be the efficiency of photosynthesis as it would be the necessity of sequestering the organic material in places where it is not reoxidized. Deep sediments would be ideal, but in order to have these we would need to already have an active hydrological cycle with deep stable basins (1991).

This was not such a problem on earth, because our transition to an oxygen rich atmosphere took around 2 billion years, much longer than 100,000 years. As oxygen accumulated, the anaerobes retreated to unaerated environments and the newly evolved aerobic organisms took over the surface. Those who were not toxified by oxygen were able to profit from the more efficient metabolism it provided and eventually dominated. On mars, however, there would not be as much time for this process to unfurl. Anaerobic organisms may perish and the ecosystem and biosphere be disrupted. Their remains could provide biomass for the organisms to come. But there is a risk of failure that will need to be considered if the decision is made to proceed from ecopoesis to terraformation.

If it is possible to create this new thickened atmosphere on mars, we should also consider how long it will remain without intervention. The dominant loss mechanism of CO₂ will most likely be the formation of carbonate rocks. Pollack et al. have estimated that the lifetime of a thick CO₂ atmosphere in mars is on the order of 10⁷ years without any recycling.

McKay et al. have written a condensed terraforming scheme that sums up what has been said so far:

Production of CFC's or other greenhouse gases to warm the surface by 20K. The regolith and polar caps then release CO₂, raising the pressure to 100 mbar. Depending on how much CO₂ is present in these it might be necessary to release additional CO₂ from carbonate materials. At this point, somewhere between 100-105 years, mars may be suitable for plants. If there was a method for sequestering them, these plants could slowly transform the CO₂ into O₂ over a period of about 100,000 years. If enough N₂ could be released from the soil and the CO₂ kept low enough, a human breathable atmosphere could be produced. Continued production of CFCs would be required over the entire time period. This proposed process relies only on mechanisms that have been demonstrated and are in fact happening on earth today (1991).

I have mentioned in passing the possible use of biologic organisms in the terraformation process, and would like to expand upon that now.

Using Biology

Thomas, in his article for the British Interplanetary Society, says "I believe that the ultimate goal of terraformation or ecopoesis should be the establishment of a self-regulating environment and that biological means of terraformation are the most appropriate in attaining this goal" (1995).

The following chart shows several terraformation problems, as well as ways biology could be used to solve these problems:

Problem Solution

For plant, algal and bacterial life (ecopoesis):

Lack of tectonic activity precludes geochemical cycling Design biological cycling systems to replace geochemical cycling (e.g. burial of fixed carbon)

Initial O₂ is too low for the normal metabolism of higher plants Use cyanobacteria and algae to increase O₂

Initial N₂ is too low for most N-fixing bacteria Select colonizing organisms that are capable of fixing N at low N₂; consider genetic engineering to improve terrestrial bacteria

High UV radiation Increase O₂; select colonizing organisms that are resistant to UV damage

Additional problems for human habitability (terraformation):

Engineered Martian atmosphere CO₂ is too high Initial colonization with photosynthetic organisms; burial of fixed carbon to prevent remineralization

O₂ too low for human habitation See previous

Lack of sufficient buffer gas (N₂) Denitrification of possible nitrate reserves by bacteria

(Thomas 1995)

Introduction of oxygen by photosynthesis would create an ozone layer would form as sunlight stuck the oxygen, causing it to react with free radicals. Photo dissociation of CO₂ to O₃ and CO might also generate sufficient ozone to produce an ozone layer. The thickness of an ozone layer can vary from place to place, so depending on how much ozone is formed, there might be areas on mars where coverage drops below a threshold level.
Seasonal and latitudinal variations in dust and cloud opacities can induce as much as a 40% variance in ozone thickness. This happens because ozone photo dissociation rates are greatly reduced by dust absorption, causing an increase in concentration.
(Smith 2001)

In late winter, there is a hemispherical asymmetry in dust and cloud opacities on mars which could cause a corresponding 10-20% asymmetry in ozone coverage. In the polar areas of mars, dust absorbs or scatters most UV radiation before it strikes the cap. Therefore, creating such a dust storms could theoretically provide UV protection and create more ozone in areas where holes develop. Dust storms could be created by preferentially heating one spot on the planet to create a pressure differential, i.e. wind (Hiscox)

Mars is covered by a layer of group up rock and fine dust known as regolith. This regolith is primarily montmorillonite, a mixture of oxides of silicon, iron, calcium, aluminum, and titanium in varying proportions. To convert this substance into soil, it will be necessary to add organic matter. On earth, this organic matter comes from decayed vegetation that is broken down by microorganisms. On mars, where there is no vegetation to decay, the dead bodies of the microorganisms themselves will provide the organic matter needed to build up the soil. The trick is finding the right microbe. Because early mars will not have rainfall, and therefore no soil moisture, these organisms will need to be able to utilize water vapor.

One that looks promising is the cyanobacteria Chroococcidiopsis. What makes this such a good candidate is its ability to survive in a wide range of extreme environments that are hostile to most other forms of life, such as hot springs, hypersaline habitats, arid deserts and the Ross Desert in Antarctica. It is often the only living thing that survives, but it gladly gives up its dominance when conditions enable other more complex forms of life to thrive. It is often found in regions of desert pavement, living beneath translucent sandstone pebbles. These pebbles serve as a moisture trap and UV shield.
(Friedmann 1995)

Another possible pioneer organism is the bacteria Deinococcus radiodurans, which can withstand extreme amounts of radiation such as the UV radiation found on Mars. In addition it has proven to be resistant to the effects of peroxides and other oxidizers that were found in the soil of Mars by the Viking lander. When subject to desiccation and freeze-drying the organism also fares remarkably well, causing it to be termed a "polyextremophile." These resistances are due to a multilayerd cell wall and an efficient and highly accurate DNA repair system possessed by the microbe. Theoretically, the organism could be genetically engineered to perform needed work on mars, such as detoxifying the soil. Conversely, studying it could reveal how to generically engineer other organisms to be more UV resistant.
(Hiscox 1995)

Friedman at al. suggested using thecyanobacterium Matteia to release CO₂ from carbonate rocks. This organism is desiccation resistant and has the ability to fix nitrogen when nitrogen compounds are unavailable from the surrounding medium. Its most important characteristic is its ability to dissolve and bore through carbonate rocks. Therefore, the organisms could be used in the initial stages of ecopoesis to release CO₂ in the atmosphere. Later it could play a role in carbon cycling, since mars would has no volcanoes to remit carbon back into the atmosphere. Whether purely biological cycles such as this could replace geochemical ones totally is a large problem facing researchers in biological planetary engineering.
(Friedmann 1993)

The cycling of sulfur should not present a problem, however the cycles of other non-volatile relatively insoluble materials such as phosphorous, iron, manganese and magnesium may be seriously affected by the lack of tectonic activity on mars. These elements will eventually be lost in deep water sediments, so periodic dredging/mining and refertilization of the ecosystems may be required.

Species in the genera Pseudomonas and Alcaligenes may be well suited to the task of converting nitrate in the soil to N₂ and N₂O. These could not be introduced until after photosynthetic populations had fixed enough carbohydrate for the growth of heterotrophic organisms, but before appreciable increases in atmospheric O₂. As O₂ increased, their activity would decrease, unless they occupied an anaerobic habitat.

In addition, some microorganisms convert nitrate deposits into ammonia (NH₃) which is a powerful greenhouse gas. Other microorganisms produce methane (CH₄), another greenhouse gas that might have been a constituent of the paleo Martian atmosphere. Methane is rapidly photo-disassociated by UV radiation, but an increase in ozone and steady biological production might lead to net accumulation.

In fact researchers have been using a device called The Andromeda Chamber to see if they could grow methanogens (microbes that release methane as a waste product) in simulated Martian conditions. So far, these organisms are able to grow at low pressures in an atmosphere that consists solely of hydrogen and carbon dioxide. They are growing in a soil derived from volcanic ash that approximates the composition, grain size, density and magnetic properties of the Martian regolith.

Plant coverage could be used to lower the total albedo of mars, increasing absorption of solar radiation and leading to further heating. The rainforests in Amazonia and Zaire do this on earth now. Mineral deposits (carbonates and nitrates, etc.) may be located in ancient evaporite basins. These may be ideal areas for establishing pioneer ecosystems, especially if they can be found at equatorial latitudes (maximum surface temperature) and low elevations (maximum surface pressure).

The figure below depicts the nutrient and energy flow in a Martian community designed for ecopoesis. Although there are more nutrient cycles than those shown (principally phosphorous and sulfur), carbon, nitrogen and oxygen are of most concern.

(Thomas 1995)

Thomas mentions that all too often the biological processes in terraformation are treated as an engineering problem. Plants are seen as a "black box" in which energy and raw materials are put in, and products come out. More energy and more raw materials = faster terraformation. It is not always that simple, especially in an unknown environment. These organisms have a narrow range of parameters they will functions over, and that range is often specific to individual species and individual cells. Much more detailed information about the Martian environment is needed (1995).

Mars Analogs

Besides sending explorers to mars, the next-best way to get this information is to research the areas of earth that are most like Mars. These areas are known as mars-analogs. For example, to deal with cooler temperatures, genetic engineers could borrow heavily from Earth's arctic creatures, many of which have an 'antifreeze' glycoprotien in their blood to prevent ice particles from growing as well as the ability to freeze their extremities and later thaw them out with no ill effects. Medical technology already uses these protein to develop medicines for hypothermia and frostbite victims.

Studying organisms on earth that inhabit regions of the earth that best approximate mars' environment is a good way to define a minimum temperature and humidity for pioneer organisms. The cold dry Ross Desert regions of Antarctica is one such place. Air temperatures there range from 258 - 273 K in the summer and can drop as low as 213 K in the winter. Relative humidity ranges from 16 - 75 percent. After planetary engineering conditions in mars could be relatively similar, apart from higher pressure and less UV radiation on earth.

The Ross Desert regions are home to a variety of endolithic organisms (organisms that live just under the surface of rocks). These organisms only exhibit metabolic activity when the temperature of the rocks raises above 263K, so this can be taken as a minimum surface temperature required for ecopoesis. The lichens there begin photosynthesis when the relative humidity raises to 70%. In times of stress they can use melt water as an alternative source. Pioneer organisms might be able to be adapted or genetically engineered to be even more tolerant to desiccation than this.

Navaro and Heath have discussed the importance of trees as biological instruments of change. They produce a lot more biomass and more oxygen than microbial ecosystems. These researchers suggest that understanding when the first tree can grow on Mars is analogous to understanding what sets the tree line on tropical mountains. In fact, one can imagine how mars would develop biologically by imagining a descent down a tropical mountain. The highest tree line on Earth occurs on Pico de Orizaba in Mexico, and this is under intensive study (NASA Ames 2000).
Another location under study is Devon Island, which is our nations largest uninhabited island, located about a thousand miles from the north pole.
A research project called the NASA Haughton-Mars Project is going on there to test new technologies and strategies that will help in exploring Mars. The island has been selected for this project because it is home to one of the highest latitude impact structures known to earth: Haughton Crater. This crater was formed 23 million years ago from a comet or asteroid collision. Mars today is covered with many impact craters. Haughton crater is the only impact structure on earth set in a true polar desert, a place that is cold, dry, windy, barren, rocky, dusty, drenched with ultraviolet light, and almost unvegetated. The average temperature there is -17° C, compared with -60° C on Mars. So, while is still far from being as harsh as Mars, its is still a step in the right direction and a good place for conducting mars-analog research.

Conclusion

At the present time, all research into planetary engineering is concerned with defining the boundaries of the possible, rather than charting some definite course into the future. The concept can no longer be described as fantasy, but confirmation of its practicality awaits a detailed exploration of mars. It is speculated that the desire for terraforming will be a driver for developing new technologies, which will in turn define a leap in human power over nature as dramatic as that which accompanied the creation of post-Renaissance industrial civilization (Zubrin et al.). Almost certainly if the first steps toward ecopoesis are taken, the developments required to complete the job will eventually follow. For what is ultimately at stake is an infinite universe of habitable worlds. The main reason for exploring and settling another planet may be the same reason new continents have always been explored and settled: because they're there.

References

Fogg, Martyn J. "Terraforming Mars: A Review of Research" http://www.users.globalnet.co.uk/~mfogg/paper1.htm

Friedmann, E.I. and R. Ocampo-Friedmann, "A Primitive Cyanobacterium as Pioneer Microorganism for Terraforming Mars," Adv. Space Res., 15(3), 243-246 (1995).

Friedmann, E.I., M. Hua, and R. Ocampo-Friedmann, "Terraforming Mars: Dissolution of Carbonate Rocks by Cyanobacteria," JBIS, 46, 291-292, (1993).

Hiscox, J.A. and D.J. Thomas, "Genetic Modification and Selection of Microorganisms for Growth on Mars," JBIS, 48, 419-426 (1995).

Hiscox, Julian A. "Biology and the Planetary Engineering of Mars." Department of Microbiology, University of Alabama.

"Mars' Magnetic Patchwork May Protect Atmosphere" Space Daily. Berkeley, Dec 2000. http://www.spacedaily.com/news/mars-atmosphere-00b.html

McKay, Christoper P., Owen B. Toon and James F. Kasting "Making Mars Habitable." Nature, 352, 489-496. (1991).

McKay, Christopher and W. Davis, "Duration of Liquid Water Habitats on Early Mars," Icarus, 90:214-221, (1991).

Nedell, S. S., S. W. Squyres and D. W. Andersen. "Origin and evolution of the layered deposits in the Valles Marineris, Mars." Icarus 70, 409-441. (1987).

Smith, Andrew and Robin Guha. "How Could we Terraform Mars?" Earth to Mars. Science in Space 2001. http://www.users.globalnet.co.uk/~smithi/mars/how.htm

"The Physics and Biology of Making Mars Habitable." 10-11 Oct 2000 at NASA Ames. http://web.mit.edu/mmm/www/summary.html

Thomas, David J. "Biological Aspects of the Ecopoises and Terraformation of Mars: Current Perspectives and Research" Journal of the British Interplanetary Society. Vol 48, pp 415-118. (1995).

Zubrin, Robert M. and Christopher McKay. "Technological Requirements for Terraforming Mars" http://www.users.globalnet.co.uk/~mfogg/zubrin.htm

Return to Aubrey's George Mason University School Bag

Species	Abundance by Volume	Partial Pressure
CO₂	0.9532	7 mbar
N₂	0.027	0.2 mbar
Ar	0.016	Minor
O₂	0.0013	Minor
CO	0.0007	Minor
H₂O	0.0003	Minor
Ne	2.5 ppm	very minor
Kr	0.3 ppm	very minor
Xe	0.8 ppm	very minor
O₃	0.04 to 0.2 ppm	extremely minor

Component	Limits	Reason
Average Global Temperature	At least 0° C	Freezing point of water
Total Pressure	> 10 mbar	Water vapor pressure plus O₂, N₂ and CO₂
CO₂	> 0.15 mbar	Photosynthesis
N₂	1-10 mbar	Nitrogen fixation
O₂	>1 mbar	Plant respiration

Component	Limit	Reason
Total Pressure	> 500 mbar	High elevation studies
CO₂	< 10 mbar	Set by toxicity
N₂	> 300 mbar	Buffer gas
O₂	130-300 mbar	Hypoxia (lower limit), flammability (upper limit)

Problem	Solution
For plant, algal and bacterial life (ecopoesis):
Lack of tectonic activity precludes geochemical cycling	Design biological cycling systems to replace geochemical cycling (e.g. burial of fixed carbon)
Initial O₂ is too low for the normal metabolism of higher plants	Use cyanobacteria and algae to increase O₂
Initial N₂ is too low for most N-fixing bacteria	Select colonizing organisms that are capable of fixing N at low N₂; consider genetic engineering to improve terrestrial bacteria
High UV radiation	Increase O₂; select colonizing organisms that are resistant to UV damage
Additional problems for human habitability (terraformation):
Engineered Martian atmosphere CO₂ is too high	Initial colonization with photosynthetic organisms; burial of fixed carbon to prevent remineralization
O₂ too low for human habitation	See previous
Lack of sufficient buffer gas (N₂)	Denitrification of possible nitrate reserves by bacteria