Colonizing Mars will be a significant endeavor with many moving parts and critical decisions to make. One of the most important decisions is how to design the appropriate food supplementary methodology for the colonists as Martian environmental conditions differ significantly from Earth. This difference demands a clear and transparent strategy to ensure the safety and productivity of future colonists. Fortunately there is sufficient predictability and routine with regards to creating this food production strategy making it easier to compare and contrast competing options.
The first element to understanding the dietary requirements for Martian colonists is deducing the minimum requirements for survival on Earth. The typical energy recommendations for a sedentary individual approximately 70 kg are about 2,000 calories, which should be familiar to most individuals because it is the basis of daily recommended allowances for nutrients used by the FDA. There is the argument that more active individuals will require double that at 4,000 to 4,500 calories. Some reference that most astronauts involved in the Apollo missions consumed an average of 2,793 calories, but their missions were extremely short (less than a week).
A more apt reference comes from Biosphere 2 where participants consumed 2,216 calories per day, but even at these consumption levels participants lost an average of 8.8 kg over the 2-year experiment. Unfortunately it stands to reason that Martian colonists will be more active than Biosphere 2 participants due to required frequent extra-vehicular activities (EVAs) to construct additional elements to expand the initial habitat and scientific exploration. Also there is little information regarding how nutrition needs and absorption capacity change in a low gravity environment, especially with regards to gut bacteria.
Another problem is that these calories need to include the 9 essential amino acids for healthy adults: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and
histidine. Studies on a minimal diet required for survival included 10 different foods: soybean, peanut, wheat, rice, potato, carrot, chard, cabbage, lettuce and tomato with recommendations for additional nutrients from sugar beets, broccoli, various berries, onions and corn.1 Unfortunately it is unlikely that such a wide array of foods will be available for a Mars colonization mission past the food that initially travels with the colonists. In addition early on in the expedition colonists will have to eat additional food brought from Earth to compensate the lack of sufficient growth on Mars.
However, the weight and cost of carrying a large amount of food with the colonists could be crippling. A general estimate can be made using MRE information. Each MRE contains about 1,200 calories.2 A colonist would consume at least two MREs per day. The general average weight of an MRE is estimated at 635 grams or slightly under 1.4 pounds.2 Therefore, the average weight of food for a day per colonist is 2.8 pounds. The generic cost associated with launching something into space is 8,000 – 10,000 dollars per kilogram (i.e. 3,636 – 4,545 dollars per pound), thus 3.716 million to 4.645 million dollars per colonist per year in food costs. Some could argue that this price is lower due to the activities of Space-X, but most people forget that these estimates are not made to scale. There is a big difference between $2,000 per pound when launching 2,000 pounds and $2,000 per pound when launching 200,000 pounds. Also any estimate can be made depending on how much money a company is willing to lose on a launch. Unfortunately cost is not the only limiting factor for colonists bringing their own food.
Some could argue that the nutrients provided by some of these foods can be substituted through vitamin consumption, but there are lingering questions about nutrient absorption when vitamins are principally responsible for nutrition. Another more minor concern revolves around shelf life for freeze-dried and MRE-type packaging, which will limit the use of initially sent food to a maximum of approximately 2 years. As stated above this concern should not be significant because greater than average food consumption will be expected due to activity levels and a lack of grown food. Finally for some there is the continuing pseudo concern of unappetizing food in space due to the specific cooking and harvesting techniques required for reduced gravity environments. This concern is rather meaningless because if someone has the choice between eating something boring, repetitive and unappetizing or dying, any sane individual will select the first option.
Based on the anticipated workload and a difficult living environment (pressurized homes and bulky pressurized spacesuits) all settlers on Mars will require additional calories beyond average consumption levels. While freeze-dried food shipments can be delivered periodically from Earth the costs associated with such missions, as estimated above, should prohibit executing this strategy indefinitely. Overall the reality is that some form of food synthesis/production methodology needs to be created for Martian colonists.
Obviously growing food on Mars will be difficult because the lack of quality soil, rainfall and consistent sunlight will force all growth to occur indoors in a pressurized environment under artificial light in a hydroponic or aeroponic infrastructure. The advantages to using soil versus a nutrient baths are numerous including, but not limited to: 1) soil playing a significant role in air purification; 2) acting as a central and low energy recycling and composting system for various types of waste; 3) difficulty re-supplying nutrient solutions away from Earth potentially limiting the lifespan of a hydroponic or aeroponic system; 4) increased gaseous aeration and reduced water leaching in the presence of no toxic agents due to the gravity difference.
Clearly somehow incorporating soil would be a large boon to the colonization process. Some individuals have very optimistic notions that the soil can be rehabilitated to the point where it can support food growth. Some initial experiments argue that it is possible to grow food in Martian soil.3 However, this research has its concerns in that the soil used to emulate the Martian soil was free of contaminants along with a lack of pressure and gravitational changes inherent to Mars, thus perceiving these results as accurate to cultivation on Mars is irresponsible. A rehabilitation process will take years, if not decades, and more than likely will not start until after colonists have made landfall.
The problems with this rehabilitation process are as followed: 1) high concentrations of detrimental agents including various salts, oxides and toxins, especially chlorine and aluminum; 2) impurities heavily reduce water uptake efficiency, which due to the lack of available water on Mars would dramatically reduce yields; 3) a theoretical lack of ability to support continuous microorganism growth which is essential for quality soil health; 4) a lack of important secondary nutrients that foster plant growth like boron and molybdenum; 5) pH of regolith soil can vary from place to place, similar to Earth, but the variations on Mars are more radical. pH will be very low in places with large amounts of jarosite and very high in places with large amounts of NaHCO3 and Na2CO3. Neutralization of these high acidic or basic regions would require large amounts of CaCO3 or olivine deposits and peat moss respectively. 6) A direct lack of principle nutritional agents most notably nitrogen and phosphorus. Some argue that nitrogen can be created through weathering, a process that will take far too long, or nitrogen fixation through various microorganisms, a process that is questionable due to existing soil conditions and a lack of phosphorus. Phosphorus only seems available through fertilizers and also requires leaching CaSO4 deposits to avoid phosphorus interaction before plant absorption. Therefore, it is unreasonable to assume outdoor food growth for the first few decades.
Some have argued that even if the Martian soil cannot be utilized the Martian atmosphere could be due to its high CO2 percentage. While approximately 95% of the Martian atmosphere is CO2, the total concentration of CO2 is much smaller than the concentration of CO2 in Earth’s atmosphere because the Martian atmosphere is dramatically thinner. Therefore, on its face there is not enough CO2 available to allow free flow of air from the Martian atmosphere to produce a net benefit in plant growth. Even if CO2 concentrations were large enough the frequent dust storms with additional regolith deposits would cause significant problems for the free airflow greenhouse and it would be incredibly difficult to filter these elements due to their very small particle size. So currently it stands to reason that all food growth in a Martian colony for the first few decades will require complete isolation from native Martian conditions.
With the lack of viable soil the most popular strategies for growing food on Mars have been to forego soil use altogether and use hydroponics. Hydroponics eliminates the soil issue, but it raises its own concerns regarding water use and nutrient supplement. Even with high rates of recycling, water scarcity will be an issue on Mars and growing food through hydroponics will place further stress on that scarcity. While some hydroponic proponents report that hydroponics actually save water, these assertions are born from a comparison between hydroponic use and flood irrigation in traditional fields rather than drip irrigation. When compared against drip irrigation, hydroponics results in slightly greater water use. Also although soil is not used, a special nutrient mixture is required and it may be difficult to mass synthesize this mixture on Mars after the initial sample is consumed without having some base to work from that must either be created on Mars or sent from Earth.
Another option for food growth is aeroponic growth. Aeroponics attempts to optimize plant growth through the use of a pressurized water mist doped with nutrients sprayed on the entire exposed root system of the plant. One of the chief reasons aeroponics is successful is it does not require soil, which can provide growth inefficiencies due to poor drainage or lack of porosity limiting root aeration leading to reduced growth. NASA has even suggested that aeroponic-based food production through an ultrasonic technique will result in similar yields to conventional growth at 45% greater rates of growth despite using 99% less water and 50% fewer nutrients. However, this conclusion must be tempered with the fact that the comparison is more than likely (it is not specified) being made against crops raised through flood irrigation and fertilizer saturation, two common yet incredibly inefficient agriculture techniques, thus the actual benefits of aeroponics over more responsible farming are more muted.
The most significant detriment to aeroponics in normal conditions is a higher probability of pathogenic death due to root exposure, but this concern is somewhat mitigated due to the natural aseptic environment on Mars limiting the absolute probability of exposure. Additional sanitary elements can be added to an aeroponics system to limit contamination from colonists. A secondary problem may be synthesis of additional nutrient compounds for the mist for traditional farming develops nutrients from organic compounds and bacteria.
Significant research has been conducted by NASA and other NASA sponsored outside researchers since the early 1990s resulting in several effective water droplet nebulizer technologies and a low mass polymer aeroponic apparatus.4 Some inflatable growth chambers have also been developed for flora growth in space. With that said some argue that a growing area is not necessary in a Martian habitat because aeroponic structures could be incorporated within various other parts of the habitat resulting in more efficient use of overall available space. While aeroponics is viewed by some as the future of food growth in space no serious long-term aeroponic experiments have been conducted in space, so most of the supposed benefits remain theoretical. Note the lack of experimentation for such a system on Earth. None of the numerous “Martian Simulation” experiments have extensively utilized aeroponics in an isolated environment to support food production. If aeroponics is viewed as a valid option for providing food on Mars why have these simulation experiments failed to incorporate such a testable strategy?
Random deployment of aeroponic systems throughout the habitat seems inefficient due to lighting condition confliction. Regardless of growth medium, plants will benefit from exposure to a different wavelength of light over standard white light. Monochromatic blue and red lights have all demonstrated positive growth influences on plants and some positive results have been recorded for green, typically ordering from red to blue to green.5 Therefore, it stands to reason that all potential crops should be exposed to either a red or blue light source preferably from a LED. However, consistent exposure to red or blue light during wakeful hours could have a detrimental effect on the crew. Due to the possible lighting conflict as well as potential sanitation issues localization of food growth to isolated areas of the habitat principally responsible for food growth is advisable or its own future constructed habitat completely isolated from the principle habitat.
One final note when deciding between hydroponics and aeroponics is the issue of yield vs. available space. If an aeroponic system is properly designed it can maximize space utilization of the habitat module by using walls and ceilings. A hydroponic unit will have to compete for space that could be utilized for storage, manufacturing, sleep, leisure, etc. Alleviating this potential space problem would involve sending to habitation modules to Mars where one would act as the living unit and one would act as the farming unit devoted to hydroponic use. While clearly the costs of such a plan would be significant due to weight issues, success would allow for special oxygen/CO2 customization of the farming unit, which would reduce the complexities of isolating the farming and living units in the same habitation module. This farming unit could also be constructed on Mars using in situ resources to avoid weight based travel complications.
When addressing the food itself, while it would be ideal to grow a wide selection of fruits, vegetables, nuts, etc. to increase moral through variety of food choice, for the first group of colonists the lack of viable Martian soil converts space into the limiting factor with water close behind. Therefore, it is important to identify the foods that give the best “bang for the vitamin buck” with regards to growth space. As mentioned early on most foods that will be grown on site will require either hydroponics or aeroponics, thus growth method combined with space considerations will make it difficult to grow various vining plants like tomatoes, cucumbers, peas, grapes, etc. Also large surface area or volume crops like corn, squash, melon, zucchini, etc. would be ill advised. Due to the additional energy requirements for colonists, especially those actively searching or building on Mars, a large source of complex carbohydrates should be grown. There are numerous quality candidates for carbohydrates namely cassavas, soybean, sweet potatoes and lentils.
Of the possible carbohydrate options the cassava root is an attractive one. One of the principle advantages to the cassava is that it is significantly drought tolerant and capable of growing well in sub-optimal soils. Clearly these elements are advantageous in a water uncertain environment like Mars where any water savings that can be created is a benefit and a non-optimal nutrient mix could become the norm. There are two types of cassava, sweet or bitter and while bitter is preferred on Earth due to its enhanced pest deterrence, the lack of these organisms on Mars would make sweet a better choice for a more appetizing meal. The purpose of growing cassavas is to harvest the root, thus the leaves of the plant can be pruned early in its growth cycle to limit space use. However, if insects are also being cultivated, the leaves can be harvested as a secondary food source. The roots are good sources of calcium and phosphorus, which are critical elements for bone structure, as well as vitamin C.
In contrast to cassavas, sweet potatoes are more finicky in their growth requiring lots of light and warm temperatures (70-80 degrees F) along with significantly more water. Most varieties of sweet potatoes have some vining characteristics, which could create space issues, but there are bush-type varieties that should be used instead. Due to near immediate consumption sweet potatoes grown on Mars will not be cured eliminating that processing step. Sweet potatoes provide significant concentrations of fiber, beta-carotene, calcium, phosphorus and vitamin A. Overall it seems reasonable that there would be a competition between either using sweet potatoes or cassava with cassava having more overall nutrients and sweet potatoes having better flavor and concentration of certain nutrients like vitamin A.
Lentils are an edible pulse of the legume family and are widely grown throughout the world for its high protein and general nutritional content. Lentils contain essential amino acids phenylalanine, valine, threonine, tryptophan, leucine, isoleucine, lysine and histidine, lacking only methionine. Some report that sprouted lentils contain methionine.6 In addition to the large essential amino acid complement, lentils also have significant amounts of fiber, folate, iron and vitamin B1. However, while lentils have a wide variety of essential nutrients their preparation is more complicated than most foods requiring long-term soaking in warm water to reduce phytate and trypsin inhibitor content. This additional use of water beyond simple rinsing may give pause to the use of lentils as a food source in the initial stages of a Mars mission.
Another quality option outside the starchier ones above is broccoli. Broccoli is high in fiber, vitamin C, vitamin B2, Pantothenic acid (B5), vitamin B6, folate (B9), manganese and phosphorus along with numerous alleged anti-cancer and immune regulatory molecules like selenium and diinodlylmethane. A secondary advantage, beyond the high nutrient value, is that broccoli is resilient, grows quickly and is harvested easily. The one possible concern for broccoli is the total area of the leaves can become large, but these leaves can be pruned to eliminate this concern. Currently there is little reason to exclude broccoli from the food options for Martian colonists.
Soybeans are commonly considered a quality choice for Martian food because they are a source of complete protein (a food that contains significant amounts of all essential amino acids) in addition to it being a quality source of protein. However, there are some concerns. First, similar to lentils above soybeans must be cooked with “wet” heat to destroy trypsin inhibitors, which will take time and additional water resources. Second, modern cultivars typically reach a mature height of 3-3.5 feet, which could create space concerns depending on where the soybean crop is planted, especially for hydroponic strategies. If soybeans were grown, pruning would more than likely be required.
Keeping with the theme of green vegetables, spinach is another quality option. Rich in lutein (for the eyes), vitamins A, C, E, K, B2, B6, magnesium, manganese, folate, betaine, iron, calcium and phosphorus. It is also a quality source of folic acid, which has been in rather short supply for the other candidates mentioned so far. Also the inclusion of peanuts could be an interesting possibility. Peanuts are high in fiber, folate, niacin (B3), phosphorus, vitamin E and magnesium along with large concentrations of protein, much more than can be acquired from fruit and vegetable candidates. Some may argue that growing peanuts hydroponically is difficult because of the burrowing flower stem; however, peanut blossoms have successfully buried themselves in nutrient media and formed viable peanuts. Therefore, there is nothing to be concerned about under normal conditions, whether or not Martian gravity changes that is unknown.
A brief note regarding genetic engineered crops. There are two schools of thought regarding the inclusion of these types of crops. Proponents would argue that it is advantageous to genetically engineer all of the seeds that colonists bring with them to Mars for drought resistance, additional vitamin synthesis (i.e. Vitamin A in golden rice) and maximum photosynthetic efficiency. Due to the use of hydroponics each plant can be semi-isolated restricting the possibility of cross contamination if something goes wrong. Opponents would argue that this isolation is rudimentary and that if something were to go wrong from a genetic standpoint then the colonists would be put at severe risk depending entirely on food from Earth. Logically it makes sense for colonists to avoid homogeneity by having a variety of seed types some that have been engineered and others that have not and plant accordingly.
This combination of plant products does not, however, completely meet all nutritional requirements, as it is low in sodium and lacks animal origin vitamins and fat such as B12 and cholesterols. This is a common feature of plant-based diets. To overcome these deficiencies sodium can be supplied in mineral form. If one concluded that the use of plant based protein sources is unreasonable due to a lack of overall content, then additional sources of protein will have to be acquired elsewhere. Utilization of large animal based protein like cows and chickens is unreasonable due to the resource demands, thus insects and fish are appropriate animal food sources in a space agro-ecosystem, given the limited area available for their rearing and for efficient use of other resources to fill the nutritional requirements.
Muscular atrophy in a reduced gravity environment is a running problem. Skeletal muscle principally involved in maintaining proper posture are most negatively affected by the reduction of gravity because this muscle has evolved to balance an environment where gravitational forces are 9.8 m/s^2. That said it appears that slow twitch muscle fibers are more susceptible to the change in gravitational force versus fast twitch muscle fibers.7,8 This difference in degradation can be troublesome because not only are slow twitch associated with posture, but are also associated with muscular endurance. In addition to muscle atrophy there is a serious drop-off (>50%) in protein synthesis rates and a significant loss of calcium balance.9-11 Whether or not this loss of calcium is due to actual direct losses or indirect absorption losses (i.e. a lack of Vitamin D) is unknown. Therefore, in order for colonists to increase the probability of limiting apoptosis a constant supply of protein will be required.
One of the key advantages to utilizing insects is that they can be fed on substances that are inedible for humans yet are byproducts from other processes. For example two of the most promising insect candidates are the silkworm (Bobyx mori) and common termites because they survive on mulberry leafs and cellulose or lignin respectively. The silkworm is the better choice of these two because it cannot escape its rearing room to become a nuisance to the colonists, it produces a useful byproduct in its silk cocoon, and colonists can consume a part of its principle food source (the berries from the mulberry plant). Termites are popular for those who plan to incorporate wood into colony construction, a strategy that does not appear to be effective in its versatility or overall usefulness. Therefore, with the obvious advantages of silkworms as both a protein source and secondary material source it stands to reason that all insect rearing should focus on silkworms.
Additional protein sources can be created through aquaculture fostering suitable concentrations of small fish. It is not reasonable to expect ideal water quality in the aquaculture, thus the selected fish must be able to effectively survive during periods of high toxicity or salinity. In addition the fish must have a small maximum growth potential to avoid resource over-consumption due to overcrowding. Understandably in most situations fish harvesting would occur often enough that overcrowding should not be an issue, but overall it pays to be careful. With these two conditions in mind the two best fish candidates appear to be loach and tilapia due to their abilities to resist negative environmental elements like poor water quality, high salt concentrations and limited water availability.
Another option for a more advanced colony is to develop an aquaponic system. In such a system plants are grown in a way where their roots are immersed in the nutrient-rich effluent water of an aquaculture. The plants should filter ammonia and other toxic metabolites that could damage the aquatic life. The water is then reintroduced to the aquaculture water pool. There are many different types of aquaponic systems, but deep-water raft seems to be the best for Mars due to its simplicity, low power requirements and greater flexibility with germination staggering because different plants have different rates of growth.
Some also argue that including algae, either hydroponically or aquaponically, should be a boon to food production. One of the most powerful reasons to include algae is that it can form a closed ecological cycle. Add the algae to an environment with water, CO2, and energy (light source) and such a system can theoretically keep a person supplied with food and oxygen for as long as the system is maintained.
For some individuals Spirulina (a type of algae) is thought to be an ideal health food and some hope that these positive traits can be maintained as a food for Martian colonists. The inherent advantages of spirulina are that it is easy to digest due to a lack of cellulose, it contains a large number of vitamins sans vitamin C and eight of nine essential amino acids, and produces a high protein by weight percentage (55-65%). However, there are some drawbacks as well most notably it ability to effectively absorb environmental elements like radiation and heavy metals including producing anatoxin as well as producing large concentrations of nucleic acids which can lead to gout if more than 50 grams are consumed in a day. In addition it has an unappetizing green slime texture and taste. While that last negative should not matter in a survival situation, from a psychological standpoint there exists a high probability that eating Spirulina day after day after day will have a negative effect.
Apart from preparing an appropriate area to grow food and selecting what should be grown, a strategy to manage produced organic waste from both humans and plant matter needs to be developed. Unfortunately there is a significant limitation in possible strategies due to a lack of available oxygen on Mars. This lack of oxygen reduces the effectiveness of traditional composting making it difficult to select as a viable strategy. Some argue that the use of Geobacter, an anaerobic respiration bacterial species, which can oxidize organic substances using iron oxides and can even generate electricity as a byproduct. However, while iron oxides are available on Mars their extraction requires work either human or machine, which adds an additional element to colonization.
Some have argued for the inclusion of hyper-thermophilic bacteria may be the best option for eliminating organic waste in an 80-100 degree C environment.12 Basically the colonists utilize a small autoclave with these bacteria resulting in organic decomposition and the elimination of harmful organisms that may reside in the waste. In addition the waste heat from the autoclave process can be released into the living environment to reduce electricity demand over a short period of time or for distilling water. However, the problem with this strategy is the oxygen requirement. For a long period of time on Mars oxygen should be in short supply, thus transferring some oxygen for waste removal processes may not be prudent. Overall the best strategy appears to be using Geobacter as a principle source of waste elimination.
In the end it is important for Mars simulation experiments on Earth to study the initial best food choices to determine how they would grow in similar conditions sans gravity changes. Unfortunately current food consumption methodologies in these simulation experiments are too well developed. While it stands to reason that there will be some initial variety born from the food transported with the colonists (albeit most of this, if not all of it, will be dehydrated or freeze dried due to the travel time between Mars and Earth), this initial source food will be consumed over a period of time (1-2 years) and less hardy choices will be relied upon for a significant time period afterwards. This misrepresentation reduces the probability of collecting accurate information pertaining to how biological functions would change over time and how colonists would have to adjust when consuming significantly fewer calories.
The next Mars simulation study should only bring a small amount of food and focus on attempting to successfully grow broccoli, peanuts, sweet potatoes, soybeans and spinach in Mars like conditions using hydroponic and aeroponic systems. The type of information born from this experiment is much more important to a successful Mars colonization mission than the simple isolation/psychological experiments because those selected for Mars will be able to handle the psychological aspects of the colonization, but they will not be able to handle starving to the point of death.
1. Hender, Matthew. “Colonization: a permanent habitat for the colonization of Mars.” 2010. http://digital.library.adelaide.edu.au/dspace/handle/2440/61315
2. Wikipedia Entry Meal, Ready-to-Eat (MRE);
3. Wieten, Jesse. “Dutch researcher says Earth food plants able to grow on Mars” Mars Daily. Jan 21, 2014. http://www.marsdaily.com/reports/Dutch_researcher_says_Earth_food_plants_able_to_grow_on_Mars_999.html
4. Clawson, James Sr. Aeroponics.com. January 1, 2012. http://www.aeroponics.com/aero43.htm
5. Kim, H, et Al. “Green-light supplement for enhanced lettuce growth under red and blue-light emitting diodes.” HortScience. 2004. 39(7). 1617-1622.
6. Wikipedia Entry – Lentil
7. Narici, M, and de Boer, M. “Disuse of the musculo-skeletal system in space and on earth.” Eur J Appl Physiol. 2011. 111(3):403-20.
8. Fitts, R, Riley, D, and Widrick, J. “Functional and structural adaptations of skeletal muscle to microgravity.” J Exp Biol. 2001. 204(18):3201-8.
9. Schollmeyer, J. “Role of Ca2+ and Ca2+-activated protease in myoblast fusion.” Exp Cell Res. 1986. 162(2):411-22.
10. Barnoy, S, Glaser, T, and Kosower, N. “Calpain and calpastatin in myoblast differentiation and fusion: effects of inhibitors.” Biochim Biophys Acta. 1997. 1358(2):181-8.
11. Haddad, F, et Al. “Atrophy responses to muscle inactivity. I. Cellular markers of protein deficits.” J Appl Physiol. 2003. 95(2):781-90.
12. Kanazawa, S, et Al. “Space agriculture for habitation on Mars with hyper-thermophilic aerobic composting bacteria.” Space Agriculture Task Force.