Growing+Plants+on+Mars

=Introduction=

Since the landing of the [|curiosity rover] and the recent launch of [|Elon Musk's Falcon Heavy and its Tesla roadster payload], the interest in the colonization of Mars has grown in popular culture. toc The question remains that once human beings get to Mars, how will a colony be able to sustain itself? Since it will not be cost effective to ship all the food and supplies needed to sustain an extended mission to Mars, the astronauts will need to grow their own crops. However, it is unclear as to whether plants are able to grow in Martian soil. This page will dive into the history of growing plants in space, discuss the effects of growing plants in low gravity, review some experimental data on current attempts to simulate/grow crops in simulants of Martian soil, discuss possible agricultural systems for a Martian colony, and look into the possibility of terraforming Mars.


 * History of Growing Plants in Space **

The first successful attempt at growing plants in space dates all the way back to 1967 with the Biosatellite II experiment which orbited the earth for three days before parachuting back to Earth. [1] However, the precursors to current space plant growth systems didn’t come along until 1983 with the launch of NASA’s Plant Growth Unit. [1] Growth systems designed after this date conducted experiments with seedlings or small species, such as [|Brassica]and [|Arabidopsis]. [1] These systems were designed to fit in a “middeck locker equivalent” space which is usually has dimensions of 20 in x 17 in x 10 in. [1] These experiments had the purpose of proving whether or not plants would grow in space and how the environment in space would effect their growth. [1] Currently, the research community has moved away from these very controlled research type experiments to more of what they call “space gardens” that are designed to supply fresh vegetables for the crew. In 2014, one of these space garden systems, called [|Veggie], was launched to the [|International Space Station] and activated. [1] Plant growth systems, like Veggie, use [|LED’s] as a light source as they can supply a better spectrum of light for photosynthesis. [1] [2] These are coupled with root modules specifically designed to work in low gravity. [2]

=**Effects of Growing Plants in Low Gravity**=

Mars has only 38% the gravity of Earth, and this has significant effects on the transportation of water and nutrients in the growing medium for plant as well as effects how gasses can diffuse throughout the growing medium. [3] [4] In current space plant growth systems, the plants are rooted in a particulate medium into which water is transferred using porous tubes that provide a [|capillary interface] between the fluid reservoir and the root zone. [1] [2] These are combined with a nutrient control system that monitor the levels of different nutrients in the root system to make sure the plants are getting the right levels of nutrients. [2] To conserve water, most space plant growth systems also condense the water transpired by the plants and recycle it to the root zone. [1] [2] These types of space plant growing systems can be adapted to similar systems for growing plants on Mars, but they would need to be scaled up. Research shows that the reduced gravity environment of Mars has some beneficial qualities. [3-5] Research groups have simulated the effects of reduced gravity on water retention and concluded that the reduced gravity of Mars allows for increased water retention in the growing medium. [4] [5] This allows for plants to waste less water, require less nutrients, and increases the time between watering cycles. [5] This will effectively reduce the amount of water needed to grow crops on Mars than you would need on Earth. [4] [5]


 * Simulants for Martian Soil **

Since there has yet to be a return mission from Mars, there is not an intact sample of Martian soil on earth, and there is not likely to be one for quite some time (15+ years). [6] Instead, NASA has attempted to recreate a simulant for Martian soil using analysis done by the different robotic exploration missions to Mars. [7] This simulant attempts to approximate the reflectance spectrum, mineralogy, chemical composition, grain size, density, porosity, and magnetic properties of Martian soil. [7] It is comprised of volcanic ash and cinders from the [|Mauna Kea] volcano in Hawaii. [7] The soil is excavated at an elevation of 1,850 m (~6,000 ft) and from a depth of 40 cm (15.75 in). It is then dried and pass through stainless steel sieves to remove all the particles <1 mm. [7] Afterwards, the soil is dried at 80 °C (176 °F) at a warehouse before it is packed into contamination proof buckets for shipment. [7] A comparison of the chemical composition of the JSC-1 Martian Soil Simulant and experimental data from the Viking 1 and 2 landers and the Pathfinder mission is shown in the following table. [7]



=**Growing Plants in Simulants of Martian Soil**=

A research group carried out a thorough comparison of growing plants in a lunar soil simulant, the previously mentioned JSC-1 Martian soil simulant, and a nutrient poor earth soil, as a control, using a wide variety of species. [8] The group chose plants from three groups, namely [|nitrogen fixers], crops, and wild plants. They chose species with relatively small seeds so the nutrient stock within the seeds was negligible. [8] This would require the plants to be dependent on nutrients available within the soil in order to allow the final results to be more standardized. [8] Their results showed that the JSC-1 Martian soil simulant performed the best as the majority of the plants species they tried to grow were able to grow significantly well, and they attributed it to its high ability to retain moisture (see Table). [8] Their results were a very good first pass at proving that crops can be grown on Mars. They noted that there can be significant improvements on their research as they were mainly testing whether it was feasible to grow plants in Martian soil rather than trying to maximize plant growth. [8]

=**Integrated Agricultural Systems**=

For true colonization, there will be a need for a self-sustaining system to feed people and recycle all the waste, and different research groups have invented different systems to accomplish this. [9] For example, all parts of the plants that are grown for crops are not completely edible, and there will be significant amounts of plant matter that can be re-purposed for other uses. [9] One possible solution, is to use different strains of bacteria to break down the plant matter into [|biofuels] for the astronauts to use. [10] Another example, is what to do with all the human excrement that will be produced by a martian settlement. The simplest solution would be to use it as fertilizer, but there are a potential risks for spreading harmful diseases if it is directly used on plants. [11] Therefore, there will need to be some form of waste management system that can break down the excrement into usable compost that has neutralized any harmful microorganisms. [11] One such system was proposed by a research group that used [|thermophilic bacteria]. [11] This system processed the human excrement and other waste products at high temperatures in order to kill off any harmful diseases and other microorganisms. [11] However, they suggested introducing thermophilic bacteria, which are strains of bacteria that can thrive in high temperature environments, to break down the waste into usable compost. [11] These recycling/composting systems, combined with the crop growing systems, are all pieces of what some research groups call integrated agricultural systems. [9] Proving that systems work is the next step that needs to be taken to see a working Martian Colony in the near future. [9]

=**Martian Environment and the Future of Terraforming Mars**=

Currently, crops cannot be grown in the open on Mars as they are here on Earth. This is due to the fact Mars has an atmospheric pressure of roughly 0.00553 atm, meaning Mars has about 0.5% the atmosphere that Earth does, and the surface temperatures on Mars can vary from -189.4 °F to 77 °F depending on location and season. [12] The lack of an [|ozone layer] also means that the surface of Mars is bombarded with harmful [|UV radiation] from the Sun. [12] [13] Not only would this kill any plants, the UV radiation would also kill almost any bacterial species that are beneficial for plant growth. [12] [13] Although these are the current conditions on Mars, data from robotic missions to Mars suggests that it was once much warmer on Mars. [13] Through [|global engineering], it could be possible to convert Mars back to something much more habitable. [13] One research group suggested that if an atmosphere could be reintroduced on Mars, it could be possible, based on Mar's geography, to have climates that range from mountain tundra to [|coniferous forests]. [13] The actual technology that would be needed to perform such terraforming is decades from being developed, but it is interesting to imagine Mars with lush forests instead of barren deserts. [13]

=**Conclusions**=

Based on the results of plant growth experiments on the ISS and the successful growth of plants in Martian soil simulant, the possibility of growing plants in Martian soil is very promising. Astronauts are currently growing crops on the ISS using plant growth systems like Veggie, demonstrating that it is possible to successfully grow crops in a low gravity environment. Combining this success with the simulation results showing that the low gravity environment of Mars has beneficial properties with regards to water and nutrient retention, makes the possibility of growing plants on Mars is even more likely. The true test, however, will be when a mission to Mars sends back large enough samples of Martian soil for experiments on Earth. Only then will all the successful results from tests using the JSC-1 Martian soil simulant be truly verified. By that time, we will have made enough advancements in researching and designing the systems necessary for a Martian colony that the prospect of building a sustainable colony on Mars will be more of a realty than a hypothetical. Once there is an established colony on Mars, then research on terraforming the Red Planet can truly begin. All of this may be years in the future, but with a focused research effort it is possible humans could be growing crops on Mars by the end of the century.

=**References**=

[1] R. Morrow, "A Brief History of Growing Plants in Space," Resource, vol. 21, (3), pp. 17-19, 2014.

[2] R. Bula, T. Tibbitts, R. Morrow, and W. Dinauer, “Commercial involvement in the development of space-based plant growing technology,” Advances in Space Research, vol. 12, no. 5, pp. 5–10, 1992.

[3] T. C. Deepagoda, S. B. Jones, M. Tuller, L. W. D. Jonge, K. Kawamoto, T. Komatsu, and P. Moldrup, “Modeling gravity effects on water retention and gas transport characteristics in plant growth substrates,” Advances in Space Research, vol. 54, no. 4, pp. 797–808, 2014.

[4] T. C. Deepagoda, P. Moldrup, M. P. Jensen, S. B. Jones, L. W. D. Jonge, P. Schjønning, K. Scow, J. W. Hopmans, D. E. Rolston, K. Kawamoto, and T. Komatsu, “Diffusion Aspects of Designing Porous Growth Media for Earth and Space,” Soil Science Society of America Journal, vol. 76, no. 5, p. 1564, 2012.

[5] F. Maggi and C. Pallud, “Martian base agriculture: The effect of low gravity on water flow, nutrient cycles, and microbial biomass dynamics,” Advances in Space Research, vol. 46, no. 10, pp. 1257–1265, 2010.

[6] Anonymous "Chlorinated Hydrocarbons; Researchers explore possibilities of growing plants on Mars," Defense & Aerospace Week, pp. 142, 2016.

[7] C. C. Allen, K. M. Jager, R. V. Morris, D. J. Lindstrom, M. M. Lindstrom, and J. P. Lockwood, “JSC MARS-1: A Martian Soil Simulant,” in Proceedings of the Sixth ASCE Specialty Conference and Exposition on Engineering, Construction, and Operations in Space, April 26-30, 1998, Albuquerque, New Mexico [Online]. Available: ASCE Library, [].

[8] Wamelink, G., Frissel, J., Krijnen, W., Verwoert, M. and Goedhart, P. (2014). Can Plants Grow on Mars and the Moon: A Growth Experiment on Mars and Moon Soil Simulants. PLoS ONE, [online] 9(8).

[9] S. Silverstone, M. Nelson, A. Alling, and J. Allen, “Development and research program for a soil-based bioregenerative agriculture system to feed a four person crew at a Mars base,” Advances in Space Research, vol. 31, no. 1, pp. 69–75, 2003.

[10] C. Verseux, M. Baqué, K. Lehto, J.-P. P. D. Vera, L. J. Rothschild, and D. Billi, “Sustainable life support on Mars – the potential roles of cyanobacteria,” International Journal of Astrobiology, vol. 15, no. 01, pp. 65–92, Mar. 2015.

[11] S. Kanazawa, Y. Ishikawa, K. Tomita-Yokotani, H. Hashimoto, Y. Kitaya, M. Yamashita, M. Nagatomo, T. Oshima, and H. Wada, “Space agriculture for habitation on Mars with hyper-thermophilic aerobic composting bacteria,” Advances in Space Research, vol. 41, no. 5, pp. 696–700, 2008.

[12] P. Rettberg, E. Rabbow, C. Panitz, and G. Horneck, “Biological space experiments for the simulation of Martian conditions: UV radiation and Martian soil analogues,” Advances in Space Research, vol. 33, no. 8, pp. 1294–1301, 2004.

[13] J. M. Graham, “The Biological Terraforming of Mars: Planetary Ecosynthesis as Ecological Succession on a Global Scale,” Astrobiology, vol. 4, no. 2, pp. 168–195, 2004.