Gaining a human foothold on another world — Mars is the obvious first case, but we can assume there will be others — will require a search for resources to support the young colony. In today’s essay, Ioannis Kokkinidis looks at our needs in terms of agriculture, whether on a planetary surface or a space-borne vessel like an O’Neill colony or a worldship. Happily, his first reference, to Lucian of Samosata, has deep science fiction roots. The author of several Centauri Dreams posts including Agriculture on Other Worlds, Ioannis graduated with a Master of Science in Agricultural Engineering from the Department of Natural Resources Management and Agricultural Engineering of the Agricultural University of Athens. He holds a Mastère Spécialisé Systèmes d’informations localisées pour l’aménagement des territoires (SILAT) from AgroParisTech and AgroMontpellier and a PhD in Geospatial and Environmental Analysis from Virginia Tech. He now lives in Fresno CA and works for local government, while continuing to pursue his interest in sustaining human life outside our own planet.
By Ioannis Kokkinidis
About noon, when the island was no longer in sight, a whirlwind suddenly arose, spun the boat about, raised her into the air about three hundred furlongs and did not let her down into the sea again; but while she was hung up aloft a wind struck her sails and drove her ahead with bellying canvas. For seven days and seven nights we sailed the air, and on the eighth day we saw a great country in it, resembling an island, bright and round and shining with a great light. Running in there and anchoring, we went ashore, and on investigating found that the land was inhabited and cultivated. By day nothing was in sight from the place, but as night came on we began to see many other islands hard by, some larger, some smaller, and they were like fire in colour. We also saw another country below, with cities in it and rivers and seas and forests and mountains. This we inferred to be our own world. We determined to go still further inland, but we met what they call the Vulture Dragoons, and were arrested. These are men riding on large vultures and using the birds for horses. The vultures are large and for the most part have three heads: you can judge of their size from the fact that the mast of a large merchantman is not so long or so thick as the smallest of the quills they have. The Vulture Dragoons are commissioned to fly about the country and bring before the king any stranger they may find, so of course they arrested us and brought us before him. When he had looked us over and drawn his conclusions from our clothes, he said: “Then you are Greeks, are you, strangers?” and when we assented, “Well, how did you get here, with so much air to cross?”
— Lucian (ca. 125–180 AD), True Story, chapters 9-11 translated by A. M. Harmon (1913).
Lucian of Samosata’s most famous work, True Story, defies easy categorization. He most likely wrote it as a parody of the travel novels popular during the Antonine Era and more specifically Antonius Diogenes’ now lost The Wonders Beyond Thule. Modern critics have called it the first surviving work of both Science Fiction and Fantasy, and ironically it is the only work of both genres that is part of the school curriculum in Greece today.
We can see that already from the earliest work of science fiction space colonization, war and agriculture are important themes. Alas, unlike Lucian’s description, who like Herodotus implores us to go and travel to the places he just described to see for ourselves that he is telling the truth, neither the Sun, nor our Moon nor Venus have an Earth-like biosphere. The use of technology, though, can allow us to produce agricultural products necessary for human survival on other celestial bodies, provided that these bodies can provide in easily available form the resources that agriculture needs. This article at first describes in general terms what sort of resources agriculture can provide, and then lists the important elements and their forms necessary for an artificial ecology to function.
When designing planetary colonization we should take note that the biosphere of Earth provides resources and ecosystem services to people through large scale cycles that are hard to replicate. It is very hard, though, to create a completely enclosed system; resource inputs of several forms will be necessary in order to maintain a system that can sustain human civilization. On Earth cultivated plants assimilate carbon from the atmosphere during the growing season, which is then released back in the short term after the end of the growing season and in the long term through the geologic carbon cycle. Until a colony reaches a very large size, which it might never reach, we will most likely try to maintain our crops in a permanent growing season, planting a crop as soon as the previous is harvested, which in turn would mean that we need to be constantly adding resources instead of allowing them to be slowly released by decomposition.
Furthermore even if we do reach a balance of agricultural inputs and outputs in our artificial ecosystem, it will likely still require a large buffer, far larger than what is being cycled every year. For example if we only use agriculture to grow food and we grow our food exclusively from plants, we only consume a small part of a plant, less than 50% of aboveground biomass for annual crops and an even smaller part of tree crops. It is simply not possible to plan to colonize a body that does not contain in significant quantities easily available elements that we need, unless we set up large scale resource transfer from outside it. I believe that I am not the first person to raise the issues below, though I have not done a systematic search in the literature. All suggestions are welcome.
Image: A fictionalized portrait of Lucian taken from a seventeenth century engraving by William Faithorne (1616-1691). Credit: Wikimedia Commons.
Resources from agriculture
Food, sustenance in all forms for the colonists, is the most readily available reason given to engage in agriculture in space. Any food grown is food that does not need to be transported from Earth, not to mention that there are a variety of psychological benefits from seeing it grow. We can divide edible crops into two categories, autotrophic organisms such as plants and heterotrophic organisms such as fungi and animals. Over the last 10 millennia we have domesticated a huge number of plants of which we eat a very wide variety of plant parts but rarely the entire plant. With heterotrophic organisms we can take advantage of the non-human edible parts of a plant and convert it into edible sources, though again we do not eat entire animals, except perhaps octopuses and their relatives. There is no such thing as the perfect diet for all conditions; we need to balance the macro and micronutrient needs of humans with the available resources and the need to maintain a healthy population. Also since plants produce their edible parts on an irregular basis we also need to store and preserve food, especially to guard against crop failure.
Usually when we talk about plants providing food and fiber, by fiber we often mean wood fiber. While we will likely see trees planted in arboretums, we are not likely to see forest style plantations for harvesting timber; colony space is too valuable and tree growth rate is too slow. Unless we can find a celestial body with forests, wood furniture will likely remain a luxury item reserved for the well off or for very specific uses where it is indispensable. Another use of wood fiber for which we will need a ready substitute is paper, it being much easier to produce paper than a factory making electronics. There is already on the market tree free paper made from bagasse, a byproduct of sugarcane processing, and several other plant waste fibers. Historically, before the invention of paper by the Chinese and its introduction by the Arabs in the 11th century to Europe, papyrus and vellum were the writing material, although it is highly unlikely that we will see vellum used in a non-ceremonial setting in space.
Moving on to other fiber uses, the most obvious one is for cloth making. Cotton fiber is the most popular of the vegetable fibers used, though other plant fibers are also used, such as flax, jute and hemp. Among animal fibers wool is the most popular, though silk and leather are also fine choices. On earth biologically derived fibers are today more expensive than petroleum derived fibers such as polyester. In practice, with the exception of Titan, celestial bodies are not known to harbor large bodies of hydrocarbons from which we can derive artificial fibers. The specific planting of crops and the selection of animals to be used in space will depend on the needs of the colony and the related infrastructure such as cotton gins that are needed to produce usable materials.
Before the industrial revolution most materials used for energy purposes were derived from the active biosphere, e.g. firewood. Today fossil fuels, biogenic in nature, mostly cover the energy needs of human civilization. There has been effort, though, to produce biofuels to substitute for fossil fuels since the oil crises of the 1970s. In Europe, which does not have large petroleum resources, coal has long been mined, and biofuels are subsidized by the Common Agricultural Policy. The purpose is not so much to cover energy needs with European resources but to keep farm prices from dropping too low and thus creating unhappy farmers that block the highways demanding better prices. In the US corn biofuel policy is more related to the political cycle, such as the first in the country Iowa caucus and its voters; after all the US is one of the largest petroleum producers in the world. The most successful bioenergy program in the world is considered to be that of Brazil, blending sugarcane derived ethanol into gasoline and thus abolishing the need for importing oil (Brazil is an oil producing country).
The use of biofuel in space is tied to the selection of the energy cycle for the colony. It is highly unlikely that we will use internal combustion engines to power a colony. Most likely energy sources will be either photovoltaics, which in the long term will require a plant to produce them out of silicon wafers, or nuclear, which requires an entire cycle of mining, refining and isotope enrichment. It is possible that we will see hydrocarbons as energy sources in the colony. Already there are plans to use abiotic processes to produce methane as rocket and rover fuel in future Mars colonies, and there it is possible to produce RP-1 from biological sources if a rocket is to require it. In general, though, I see biofuels occupying a niche source in a future colony. We might create biodiesel out of waste edible oils but we are unlikely to see entire sunflower plantations intended for biodiesel production.
According to Wikipedia there are over 300,000 tons of bioplastics produced each year, or 0.1% of the total global plastics production worldwide. Modern technological civilization is very dependent on a variety of plastics, even inside a greenhouse (e.g. drippers). Unless the celestial body colonized has prodigious amounts of easily available hydrocarbons available such as Titan, we will need to create very early an infrastructure to produce bioplastics for colony needs or else set up a logistic chain for plastics from Earth. Generally for bioplastics the feedstock is readily available plant material, such as cellulose or dextrose, though some animal sources such as casein (a milk protein) have been used. The harder part will be creating a production line for these bioplastics from the local raw material.
Elements for agriculture
What follows is a list of major elements that are necessary for plant growth. Some 17 elements are necessary for plants to survive, though the majority are required in minute amounts often easily available in the soil or as impurities in the fertilizers. Carbon, Hydrogen and Oxygen combined are responsible for 95% of plant mass. Often, though, due to pH element deficiencies can arise despite the presence of the element in the soil.
Carbon enters the biosphere when it is assimilated by plants through photosynthesis in the form of CO2. While there are a few methanotrophic bacteria known, it is unlikely that we will require carbon in any form except CO2 for agriculture. Plants can oxidize CO in the presence of O2 to CO2, but cannot use raw carbon. Thus if carbon is available in the environment but not in the form of CO2, we will likely need to set up processes to produce CO2 before plants can assimilate it.
Plants assimilate hydrogen mostly in the form of water. Water has an important function in plants both as the solvent of biology but also as the stream that allows the transport of elements inside the plant.
Oxygen as an element is assimilated by plants in the form of water and CO2. It is released to the environment in molecular form by photosynthesis, which is critical for the survival of animal life. Plants also use molecular oxygen from the environment during respiration, however they produce far more O2 than they consume, and this allows heterotrophic life to exist.
Image: The colors in the spectra show dips, the size of which reveal the amount of these elements in the atmosphere of a star. The human body on the left uses the same color coding to evoke the important role these elements play in different parts of our bodies, from oxygen in our lungs to phosphorous in our bones (although in reality all elements are found all across the body). In the background is an artist’s impression of the Galaxy, with cyan dots to show the APOGEE measurements of the oxygen abundance in different stars; brighter dots indicate higher oxygen abundance. Credit: Dana Berry/SkyWorks Digital Inc.; SDSS collaboration.
Plants require this element in a variety of forms but unlike the previous three they cannot assimilate it from the atmosphere. Rather they take it through the roots, more specifically through the soil solution in the form of nitrate. Nitrates, though, are highly mobile in the soil, which is why we also fertilize with ammonia, which is converted to nitrate by soil microorganisms over time. Both forms of nitrogen are typically produced in chemical factories on Earth using atmospheric nitrogen as a feedstock. In parts of the outer solar system they are available as rocks and ices.
Phosphorus is another element that is assimilated from the soil solution. Unlike nitrogen, though, it is not found in the earth’s atmosphere, rather we mine phosphate rocks and fertilize with phosphate salts. Some 80% of global phosphate mining exploits deposits of biogenic sedimentary rocks of marine origin. The other 20% is of igneous origin in the form of apatite. Outside earth it is this phosphoric apatite that will likely provide our phosphorus needs
Just as with phosphorus, potassium is mostly mined from sedimentary rocks, more specifically evaporites. While evaporites have been found on Mars and are likely present on Venus, for other bodies of the solar system we will need to locate other forms of the element and process it into the salts that plants require.
Iron has an intermediate position between micro and macronutrients, required in quantities that are small for macronutirents but large for micronutrients. Plants assimilate iron in ferrous (Fe++) form, often from organic iron complexes that contain ferric (Fe+++) form with the expenditure of energy by the plant. Since the concentration and availability of ferrous and ferric iron depend on the soil pH and other ion antagonists in the solution, very often we see plants with iron deficiency despite a large iron concentration in the soil and the parent rock. In hydroponic fertilization and urgent deficiency interventions we tend to use organic iron so as to provide a highly available form to the plants. Organic iron, though, is not necessary if we take pains to control the pH and antagonists such as calcium, phosphorus and carbonates.
Calcium is a micronutrient, not necessary in large quantities for agriculture. However it is often applied in macronutrient quantities in order to control soil pH. In areas of high rainfall such as the eastern US and western Greece we will find many soils that are calciferous in origin but have a low pH, because rainfall washes the Ca++ ions, lowering the pH to acid levels. Calcium is used in hydroponics to raise solution pH and it is likely necessary to stockpile and use calcium for this purpose rather than for the specific need of the plant for this element.
Sulfur is the opposite of Calcium in that it is used to lower soil pH. There is no shortage of sulfur concentration in agricultural soils on Earth; fossil fuel use has spread it far and wide. Pollution control measures have reduced atmospheric deposition in developed countries and it is likely that in a few decades sulfur fertilization will be necessary in some areas. So far, though, we are more likely to see sulfur in hydroponics, raising pH when it falls too low. Just as with calcium, plants do not require large quantities, but we may need to stockpile it for the same reasons.
The rest of the elements necessary are required in minute quantities and while pH is very important for their availability, their limited requirements mean that we will not need to seek them specifically. In general, micronutrient fertilization can become necessary and critical if we choose an agricultural system where we remove the entirety of the plant mass from the soil or substrate and do not allow any plant decomposition to take place, which is what we will do at first. The decomposing remains of the previous harvest are often the primary source of micronutrients for the next, even in intensive agriculture. If we remove the entirety of the crop each time, we will need to provide the elements that were mined in the process, though again, it is unlikely that we will need to search for extensive quantities.
This contribution was inspired by news reports of the first NASA Mars landing site selection symposium. They mentioned that along with geologists seeking interesting formations there were also colonization specialists arguing to select sites with mineral resources for metallurgy in the future colony. They did not mention plant specialists looking for areas having resources to grow plants. I did not write this contribution with Mars specifically in mind; it is intended as a general guide for all celestial bodies. Bodies with carbon dioxide in the atmosphere will not require creating it from other elements. Bodies with nitrate rocks are advantageous to those with only gaseous nitrogen in the atmosphere.
Also, while we are fortunate enough to know the surface composition of several bodies of the solar system, we just don’t know enough about exoplanets to be able to judge which are more suitable for colonization. At best we have managed to infer the presence of some elements in the atmosphere of a few exoplanets but we are nowhere near a full resource guide. Human civilization has always been dependent on agriculture for a variety of resources to survive and thrive. This will continue to be true when we move beyond Earth.