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What is the Best Protein Source for a Mars Mission?

Chloë Tucker

Abstract

Visits to Mars have been a part of science fiction for centuries, but soon they may become a

reality. Exploring Mars would be the next giant leap in the journey of humanity, because it

would mean we would be one step closer to understanding our place in the universe. There

are many discoveries to be made on Mars, it could reveal the past or the future of the Earth;

new lifeforms could be discovered; or the prolonged effect of low gravity on the human body

could be found. Mars could be a place where humanity could escape in the event of global

disaster, or be a location from which the rest of space is explored. Not to mention the

technologies that would be developed along the way, or the economic value of resources on

Mars1.

Thus far, several human Mars missions have been proposed of varying lengths. Most of these

projects focus on technologies capable of getting people to Mars. While this is important, it

becomes worthless if the humans die on Mars or during transit. Several resources are required

in order to keep a person alive: oxygen, water and shelter are just a few examples, but

perhaps the most complex resource is the diet which the space travellers will eat. The longer

the mission, the more difficult this problem is to solve. For colonisation, the food source must

fully sustain the astronauts for their entire life; it must have no nutrient deficiencies; be non-

Earth dependant and be enjoyable to consume. This report explores the best source of the

protein portion of this diet. Protein was selected because it is vital to the survival of the

human body, and would be essential when humans eventually face this unforgiving

landscape.

1.0 Introduction

1.1 What Are Proteins and Why Are They Important?

Proteins are complex molecules that play an essential role in the human body and the bodies

of all known organisms. They consist of a chain of amino acid monomers, which are attached

together in a specific order by translation in a ribosome. There are 20 different types of amino

acid used in protein synthesis, and each one has a different variable group2, 3 (as shown in

Figure 1).

1 Red Colony, ‘Why Colonize Mars?’, http://www.redcolony.com/features.php?name=whycolonizemars,

[accessed 07/12/2017] 2 Mary Jones et al. Biology, AQA A-level, Year 1 and AS, Student Book (Harper Collins Publishers, 1 London

Bridge Street, London SE19GF: HarperCollins, 2015) p.26-30 3CGP, A-Level Year 1 & AS, Biology, Exam Board: AQA (Cumbria: CGP, 2015) p.31-48

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Figure 1: The Structure of an Amino Acid

The 3D shape of the protein depends on its variable groups; they bond with each other and

other molecules to determine the shape of the finished protein. The shape of the protein helps

it to perform its function. For example, if the protein is an enzyme which needs to catalyse a

certain reaction, the shape of the active site on the protein means that the right substrate can

bind with the enzyme to form an enzyme substrate complex so that the reaction can happen.

If the 3D shape of the protein was different this reaction might not occur, which could have

catastrophic effects on the human’s body, such as not being able to hydrolyse deadly

pathogens 4, 5.

Other uses of protein include carrier and channel proteins to allow facilitated diffusion;

haemoglobin which helps to carry oxygen and carbon dioxide around the body; structural

proteins which form bone and other tissues; and so many more. Without proteins we would

be unable to survive.

1.2 Which Amino Acids Are Necessary for Human diet?

Every living organism makes its proteins from the same 20 amino acids, some of them must

come from the diet, whilst others can be synthesised. Plants must make all their amino acids

themselves, using resources from their environment. Other non- photosynthesising organisms

can consume, digest and absorb amino acids from plants, so the mechanisms required to

make all 20 are not necessary. The human body usually only needs to consume only 9

essential of the total 20 amino acids6 (shown in Table 1)7, the other 11 non-essential can be

made by a wide range processes, which usually involve intermediates of other reactions, and

other amino acids as reactants.8

4 Mary Jones et al., Biology, AQA A-level, Year 1 and AS, Student Book, p.26-30 5 CGP, A-Level Year 1 & AS, Biology, Exam Board: AQA (Cumbria: CGP, 2015) p.31-48 6 Medline Plus, ‘Amino acids’, https://medlineplus.gov/ency/article/002222.htm, [accessed 11/02/2017] 7 Elodie Foulquier et al., ‘Formula of the 20 common amino acids and structural details of the side chains’,

http://www.imgt.org/IMGTeducation/Aide-memoire/_UK/aminoacids/formuleAA/, [accessed: 25/09/2017] 8 RPI, ‘Amino Acid Biosynthesis Essential and Nonessential Amino Acids’,

http://homepages.rpi.edu/~bellos/new_page_2.htm, [accessed 11/02/17]

= Carboxyl group (COOH)

=Amine group (NH2)

=Hydrogen (H)

=Carbon (C)

=Variable Group (R)

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Table 1: Amino Acids and Their Structures 9

Essential amino

acids

Chemical

structure

Non-Essential

amino acids

Chemical

structure

Histidine Arginine

Isoleucine Asparagine

Leucine Aspartate

Lysine Cysteine

Methionine Glutamate

Phenylalanine Glutamine

Threonine

Glycine

Tryptophan Proline

Valine Serine

Tyrosine

Alanine

For example, the non-essential amino acid alanine is made from a ketoacid10 called pyruvate

which is derived from glucose during the process of glycolysis11. Pyruvate can either

continue to enter the Krebs cycle or it can be made into alanine by replacing the keto group

with an amine group (from glutamate) through a transamination reaction involving a

9 Elodie Foulquier et al., ‘Formula of the 20 common amino acids and structural details of the side chains’,

http://www.imgt.org/IMGTeducation/Aide-memoire/_UK/aminoacids/formuleAA/, [accessed: 25/09/2017] 10 Ian Hunt, ‘Aldoses and Ketoses’, http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch25/ch25-2-4.html,

[accessed: 13/03/2017] 11

Jeremy Berg et al., Biochemistry. 5th edition. Glycolysis Is an Energy-Conversion Pathway in Many

Organisms (New York: W H Freeman, 2002), Section 16.1, https://www.ncbi.nlm.nih.gov/books/NBK22593/,

[accessed 28/02/2017]

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transaminase enzyme. Glutamate is often the amine group donor and it is made from an

intermediate of the Krebs cycle its amine group comes from an essential amino acid through

a transamination reaction12, 13, 14, 15, 16, 17, 18.

It is worth noting that other molecules, for example glucose, are often necessary for these

reactions to happen19,20, though full analysis of these molecules is not included within the

scope of this report. Therefore, the essential amino acids (which are analysed) should be

included within a balanced diet which also includes sufficient amounts of other molecules

necessary for amino acid synthesis.

1.3 How Much Protein Does an Astronaut Need?

Not only the type of amino acid needs to be taken into consideration, but also the quantity.

Naturally, the amount of protein required will differ for each individual person (due to

genetics, age, height etc.), so it is logical to consider the kind of person who would be

selected to colonise or visit Mars.

Both the “Mars one” mission and NASA’s proposed “Journey to Mars21” state that candidates

need to be “healthy”22, 23, 24, this is a rather vague statement, though it can be used to estimate

the mass of an astronaut. Current NASA astronauts must have a height “between 62 and 75

inches” 25, which means that if they had a “normal” 26or “healthy”27 BMI they would have a

mass of approximately 47 kg to 87 kg, depending on their height28. With these figures, the

mean average mass of an astronaut would be 67 kg, so this mass will be substituted into any

12 Charles Obhardt, ‘Transamination Reaction’, http://chemistry.elmhurst.edu/vchembook/631transam.html,

[accessed 11/02/2017] 13 Charles Obhardt, ‘Transamination Reaction’, http://chemistry.elmhurst.edu/vchembook/631transam.html,

[accessed 11/02/2017] 14 Sal Khan, ‘Krebs / citric acid cycle’, https://www.khanacademy.org/science/biology/cellular-respiration-and-

fermentation/pyruvate-oxidation-and-the-citric-acid-cycle/v/krebs-citric-acid-cycle, [accessed 11/02/2017] 15 G. A. Abdel-Tawab, ‘The Production of Pyruvic Acid, Oxaloacetic Acid and a-Oxoglutaric Acid from

Glucose by Tissue in Culture’, Biochemical Journal, vol.72 (19/01/1959), pp.619-623 16Khan Achedemy, ‘Glucogenic and ketogenic amino acids’, https://www.khanacademy.org/test-

prep/mcat/biological-sciences-practice/biological-sciences-practice-tut/e/krebs-cycle-and-oxidative-

phosphorylation---passage-2, [accessed 13/03/17] 17 J. Simpkins et al., Third Edition Advanced Biology, (London: Mills & Boon Limited, 1980), p.16 18 Jeremy Berg et al., Sixth edition Biochemistry, (USA: Sara Tenney, 1975), p.661-695 19 J. Simpkins et al., Third Edition Advanced Biology, p.16 20 Jeremy Berg et al., Sixth edition Biochemistry, p.661-695

21 NASA, ‘NASA’s Journey to Mars’, https://www.nasa.gov/sites/default/files/atoms/files/journey-to-mars-next-

steps-20151008_508.pdf, [accessed 26/11/2017] 22 NASA, ‘Astronaut Selection and Training’, https://www.nasa.gov/centers/johnson/pdf/606877main_FS-2011-

11-057-JSC-astro_trng.pdf, [accessed 12/02/17] 23 Mars One, ‘Mars One Astronauts’, http://www.mars-one.com/mission/mars-one-astronauts, [accessed

12/02/2017] 24 Mars One, ‘What are the qualifications to apply?’, http://www.mars-one.com/faq/selection-and-preparation-

of-the-astronauts/what-are-the-qualifications-to-apply, [accessed 12/02/2017] 25 NASA, ‘Astronaut Selection and Training’, https://www.nasa.gov/centers/johnson/pdf/606877main_FS-2011-

11-057-JSC-astro_trng.pdf, [accessed 12/02/2017] 26 NIH, ‘Body Mass Index Table 1’, https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmi_tbl.htm,

[accessed 12/02/2017] 27 NIH, ‘Body Mass Index Table 1’, https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmi_tbl.htm,

[accessed 12/02/2017] 28 Ibid.

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calculations within this report. In an actual Mars mission, the astronauts real mass should be

used. The requirements of each amino acid for an adult (NASAs astronauts are usually above

the age of 2629, so they can have satisfactory qualifications) are shown in Table 2 along with

the requirements of the average astronaut30.

Table 2: The Daily Requirements of Each Amino Acid for the Average Astronaut31

Essential amino

acid

Average mass of essential

amino acid required per day

(mg/ kg of body mass)

Mass of essential amino acid

required per day for an

average astronaut (mg)32

Histidine 10 670

Isoleucine 10 670

Leucine 14 938

Lysine 12 804

Methionine 13 871

Phenylalanine 14 938

Threonine 7 469

Tryptophan 3.5 234.5

Valine 10 670

1.4 What are the Limitations of Protein Production when Travelling to Mars?

When travelling to Mars there are certain limitations which must be considered, mostly due

to the expense and confinements of space travel. The entire life support system must fit the

“Equivalent System Mass” 33, 34, 35 considerations. This is an evaluation that considers many

different factors and finds how economical it is to take the system to Mars. The total ESM

should be as small as possible for the most cost-effective journey. The calculation made for

each subsystem is shown in Equation 1 (Protein production is one subsystem)36

29 NASA, ‘Frequently Asked Questions’, https://astronauts.nasa.gov/content/faq.htm, [accessed 12/02/2017] 30 National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary

Allowances., Recommended Dietary Allowances: 10th Edition., (Washington (DC): National Academies Press

(US), 1989), Chapter 6 31 National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary

Allowances., Recommended Dietary Allowances: 10th Edition., Chapter 6 32 Refer to Appendix B for calculation 33 Julie A. Levri et al., ‘Advanced Life Support Equivalent System Mass Guidelines Document’,

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040021355.pdf, [accessed: 15/02/2017] 34 Markus Czupalla, ‘Life Support System for Pole Station’, Project Boreas: A Station for the Martian

Geographic North Pole, A Publication of The British Interplanetary Society (2006), pp.49-56 35 Harry Jones, ‘The Cost and Equivalent System Mass of Space Crew Time’

http://spacecraft.ssl.umd.edu/design_lib/ICES01-2359.crew_time_cost.pdf, [accessed: 13/03/2017] 36 Julie A. Levri et al., ‘Advanced Life Support Equivalent System Mass Guidelines Document’,

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040021355.pdf, [accessed: 15/02/2017]

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Equation 137

Where:

M= Mass

SF= “Stowage factor”

V= Volume

P= Power

C= Cooling

CT= Crewtime

In this equation, certain factors are multiplied by their “mass equivalency factors” 38(these are

written with an eq beside them), these are values which can convert factors which are not

measured as masses, into masses, this way the final ESM can be measured in kg. The masses

themselves are multiplied by a “stowage factor”39 which means the equation considers

anything used to tie down the system during transit. The mass should include every part of

the system; this includes a protein source whilst protein production is being set up; any

redundant systems, and any equipment used to set up the system once on the planet40.

There are other factors that need to be considered which are not included within the ESM

such as safety, the initial cost of the object, and how well the object can endure different

gravity; these must be considered separately along with any other issues which appear.

To conclude, there are numerous factors which need to be considered when making a protein

source for a Mars mission. However, the limitations with protein production are not clearly

defined; though it is important that system is as efficient and light as possible and fits within

the entire life support system. For a longer mission, such as a colonisation, the system should

not be Earth dependant, this means its inputs should come from Mars, and be recycled.

1.5 Resources on Mars

Humans get their protein by eating other organisms. Different organisms require different

conditions and resources, though there are some resources which are necessary for most life

on Earth, and would need to be made available on Mars. This section will look at many,

though not all, of the resources required for basic life.

Firstly, water, an essential molecule for all life on Earth. It can be found underneath Mars’

northern hemisphere, where frozen lakes are just 1 to 10m below the surface41, 42, 43. To

37 Ibid. 38 Ibid. 39 Ibid. 40 Harry Jones, ‘The Cost and Equivalent System Mass of Space Crew Time’

http://spacecraft.ssl.umd.edu/design_lib/ICES01-2359.crew_time_cost.pdf, [accessed: 13/03/2017] 41 NASA, ‘Mars Ice Deposit Holds as Much Water as Lake Superior’

https://www.jpl.nasa.gov/news/news.php?feature=6680, [accessed: 26/04/2017]

D = “Duration of mission segment”

MTD= Time dependant Mass (MTD)

VTD= Time dependant Volume (VTD)

eq= “Mass equivalency factor”

L= Initial

i= The subsystem

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access liquid water, the ice could be heated and purified using an energy source, in some

cases the organisms can purify the water themselves (for example, algae).

The main gases required for life are oxygen and carbon dioxide. All of the organisms in this

report require oxygen, even if only to start photosynthesis44, and so it has to be made

available so humans don’t have to compete with other organisms for it. Only traces of oxygen

can be found on Mars45, so a photosynthesising organism is necessary for any alternative

organism to survive. Therefore, a small amount of oxygen must be taken to the station from

Earth to initiate photosynthesis, if they ever need to grow seeds, and the crew must ensure

that the photosynthetic organisms stay alive.

The Martian atmosphere has more carbon dioxide (7.1 millibars46) than Earth’s 0.38

millibars47, 48, which means there would be enough to sustain any photosynthesising

organism. This is because Mars’ atmosphere is 95%49 carbon dioxide, but the pressure is less

than 100th of Earth’s atmosphere50, 51, 52.

Photosynthesising organisms also require light, fortunately Martian days are around the same

length as Earth days53, 54. However, there are large dust storms which can hide the sun for a

considerable amount of time, and the intensity of the light would be lower than that on Earth

due to the larger orbit of Mars from the sun.55 Therefore, an artificial light source would be

required in times of reduced sunlight.

The nutrients needed to survive are all found within the Martian soil56, in one experiment a

Martian soil ‘simulate’ actually performed better than Earth soil for growing some types of

42 Gina Anderson et al. ‘NASA Confirms Evidence That Liquid Water Flows on Today’s Mars’

https://www.nasa.gov/press-release/nasa-confirms-evidence-that-liquid-water-flows-on-today-s-mars,

[Accessed: 26/04/17] 43 William Hartmann, A Traveler’s Guide to Mars, The Mysterious Landscapes of the Red Planet, (New York:

WORKMAN PUBLISHING, 2003), p.91-100 44 UCSB, ‘Do plants have to have oxygen to survive? Or can plants (other than the plants in wetlands) live

without oxygen?’, http://scienceline.ucsb.edu/getkey.php?key=760 [accessed: 26/04/2017] 45 NASA, ‘Composition’ https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=composition, [accessed

28/04/2017] 46 Refer to Appendix B for calculation 47BBC Bitesize, ‘Oxygen and carbon dioxide’

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/earth/earthsatmosphererev5.shtml, [accessed

04/04/2017] 48 PHOENIX MARS MISSION, NASA, ‘Mars/Earth Comparison Table’,

http://phoenix.lpl.arizona.edu/mars111.php, [accessed 03/12/2017] 49 NASA, ‘Composition’ https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=composition, [accessed

28/04/2017] 50 See Appendix B for calculation 51 Jerry Coffey, ‘Air on Mars’, https://www.universetoday.com/14872/air-on-mars/, [accessed 04/04/2017] 52 PHOENIX MARS MISSION, NASA, ‘Mars/Earth Comparison Table’,

http://phoenix.lpl.arizona.edu/mars111.php, [accessed 03/12/2017] 53 Matt Williams, ‘How Long is a Day on Mars?’ https://www.universetoday.com/14717/how-long-is-a-day-on-

mars/, [accessed 28/04/2017] 54 NASA, ‘Mars Facts’, https://mars.nasa.gov/allaboutmars/facts/#?c=inspace&s=distance, [accessed:

28/04/2017] 55 First the Seed Foundation, ‘Sunlight on Mars - Is There Enough Light on Mars to Grow Tomatoes?’

https://www.firsttheseedfoundation.org/resource/tomatosphere/background/sunlight-mars-enough-light-mars-

grow-tomatoes/ [accessed 01/05/2017] 56 Gary Jordan, ‘Can Plants Grow with Mars Soil?’, https://www.nasa.gov/feature/can-plants-grow-with-mars-

soil, [accessed 28/04/17]

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plants57, 58. However, there may be an imbalance in different locations on the planet for

optimal growth, much like on Earth, so fertiliser appropriate for the area should be imported

from Earth59, or recycled from human waste products. Furthermore, toxic substances in the

soil 60, 61could be damaging to the organisms or humans eating them and so the necessary

precautions to combat this should be developed.

Moreover, because of the lack of life on Mars, bacteria, required to recycle, breakdown and

retain nutrients within the soil62, are not found on Mars. For example, while there are plenty

of nitrogen compounds in the soil63(as well as traces of ammonia64 and nitrogen in the

atmosphere)65, they may not be recycled properly and so bacteria from all parts of the

nitrogen cycle need to be taken from Earth. This should put nitrogen into the atmosphere

making conditions more similar to Earth, since currently only 1.89% of the Martian

atmosphere is nitrogen66, 67 (this is much less than Earth’s 77% 68of a much denser

atmosphere). This means that organisms such as lichens, which get their nitrogen from air,

will be able to survive69.

All of the organisms used for protein production must be contained to prevent gases from

diffusing out and restricting respiration. In the case of protein sources formed by cultures

(including any bacteria for nutrient recycling) an incubator containing a growth medium is

required70, 71. This requires power so that it can be heated, stirred and lit as necessary. Carbon

sources, gases and mineral ions should be supplied to the incubator, and it should be made

sterile before leaving Earth to prevent disease.

57 Anna Heiney, ‘Farming in ‘Martian Gardens’, https://www.nasa.gov/feature/farming-in-martian-gardens,

[accessed 28/04/17] 58 G. W. Wieger Wamelink et al., ‘Can Plants Grow on Mars and the Moon: A Growth Experiment on Mars and

Moon Soil Simulants’, http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0103138 [accessed

01/05/2017] 59 Gary Jordan, ‘Can Plants Grow with Mars Soil?’, https://www.nasa.gov/feature/can-plants-grow-with-mars-

soil, [accessed 28/04/17] 60Leonard David, ‘Toxic Mars: Astronauts Must Deal with Perchlorate on the Red Planet’,

https://www.space.com/21554-mars-toxic-perchlorate-chemicals.html, [accessed 28/04/2017] 61 Yu L et al., ‘Uptake of perchlorate in terrestrial plants.’, Ecotoxicology and Environmental Safety, vol.58,

Issue 1 (May 2004) pp. 44-49 62 Elaine Ingham, ‘THE LIVING SOIL: BACTERIA’,

https://extension.illinois.edu/soil/SoilBiology/bacteria.htm, [accessed 28/04/17] 63Nancy Neal-Jones et al., ‘NASA's Curiosity Rover Finds Biologically Useful Nitrogen on Mars’,

https://www.nasa.gov/content/goddard/mars-nitrogen, [accessed 26/11/2017] 64 BBC News, ‘Ammonia on Mars could mean life’, http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm, [accessed

13/07/2017] 65 Elaine Ingham, ‘THE LIVING SOIL: BACTERIA’,

https://extension.illinois.edu/soil/SoilBiology/bacteria.htm, [accessed 28/04/17] 66 NASA, ‘Composition’, https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=composition, [accessed

28/04/2017] 67 Jerry Coffey, ‘Air on Mars’, https://www.universetoday.com/14872/air-on-mars/, [accessed 04/04/2017] 68 PHOENIX MARS MISSION, NASA, ‘Mars/Earth Comparison Table’,

http://phoenix.lpl.arizona.edu/mars111.php, [accessed 03/12/2017] 69 United States Department of Agriculture, Forest Service, ‘Lichen Habitat’,

https://www.fs.fed.us/wildflowers/beauty/lichens/habitat.shtml, [accessed 21/07/2017] 70 BBC Bitesize, ‘Mycoprotein’,

http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/humans_and_environment/food_production/revisi

on/2/, [accessed 11/07/2017] 71 D C Graham, ‘Factors Affecting Production of Mold Mycelium and Protein in Synthetic Media.’, Applied and

Environmental Microbiology, vol.32, Issue 3 (1976), pp. 381–387

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Average temperature on Mars is -63ºC 72, this is below freezing, meaning most organisms

will require artificial heating in order to keep them alive. Furthermore, gravity on Mars is

roughly “38% that of Earth”73 which will affect each organism differently. For example,

imbalanced plant hormones could cause them to not grow properly, whereas muscle atrophy

in animals could lead to a lower protein yield.

The main limiting factors when choosing a protein source for Mars will be oxygen

concentration and temperature, since these affect all organisms. However, all resources need

to be considered when choosing a protein source, because low requirements are more

efficient.

2.0 Photosynthesising Bodies

Photosynthesising bodies would be necessary for the Martian colony, even if they aren’t used

as the primary protein source. This is because they provide oxygen and energy for food

chains, and so all organisms rely on them.

2.1 Plants

The first source of protein considered in this report is plants, as they feature as a potential

food supply in Project Boreas74, NASA’s “Journey to Mars” and in the “Mars One”

mission75. In fact, NASA has already managed to grow a type of cabbage in space using a

technology called Veggie 76, 77, 78, with hope that crews on long duration space missions will

be able to eat the food it produces.

Mars has many resources that plants require79, but there are also some large obstacles (as

mentioned in section 1.5). One problem is the temperature, most vegetables on Earth have an

optimum temperature between 10 ºC and 27 ºC 80, meaning the Martian environment is too

cold and so they are likely to need heating. To make things worse, atmospheric pressure on

Mars is less than 1% of Earth’s atmospheric pressure, which is a big issue for plants, as water

moves out of the plant by osmosis because of the low water potential outside of the plant81.

72 ‘Mars Facts’, https://mars.nasa.gov/allaboutmars/facts/#?c=inspace&s=distance, [accessed: 28/04/2017] 73 ‘Gravity and More’, https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=gravity, [accessed

29/10/2017] 74 Markus Czupalla, ‘Life Support System for Pole Station’, Project Boreas: A Station for the Martian

Geographic North Pole, A Publication of The British Interplanetary Society (2006), pp.49-56 75 Mars One, ‘Will the astronauts have enough water, food and oxygen?’ http://www.mars-one.com/faq/health-

and-ethics/will-the-astronauts-have-enough-water-food-and-oxygen, [accessed 18/07/2017] 76 Anna Heiney, ‘Farming in ‘Martian Gardens’’, https://www.nasa.gov/feature/farming-in-martian-gardens,

[accessed: 28/04/2017] 77 Linda Herridge, ‘Veggie Will Expand Fresh Food Production on Space Station’,

https://www.nasa.gov/mission_pages/station/research/news/veggie/, [accessed 02/05/2017] 78 Fin O’Connor, ‘ISS Uncovered’, YOUNG SCIENTISTS journal, 07/2016, Issue 19, pp.10-11 79 James C. Schmidt et al., ‘Requirements for Plant Growth’,

http://www.aces.uiuc.edu/vista/html_pubs/hydro/require.html, [accessed 01/05/2017] 80 James C. Schmidt et al., ‘Requirements for Plant Growth’,

http://www.aces.uiuc.edu/vista/html_pubs/hydro/require.html, [accessed 24/09/2017] 81 Daunicht HJ et al.,‘Plant Responses to Reduced Air Pressure: Advanced Techniques and Results’, Advances

in Space Research, vol.18, Issue 4-5 (1996), pp.273-281

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This slows growth; therefore, technologies would need to be developed to contain gases and

increase pressure82, 83.

Gravity on Mars is only 38% of Earth’s84, meaning that plants may not grow properly

because the plant hormones which help them grow respond to gravity. However, plants have

already been grown on the International Space Station which experiences microgravity,

which is much smaller than the gravity on Mars85, 86, 87, 88

The ideal plant to take to Mars would be able to survive in cold temperatures, low light levels

and have small amounts of water, as well producing all the essential amino acids required for

human consumption, and potentially providing extra oxygen for the station. In “Project

Boreas”89 Ipomoea batatas (sweet potatoes) are suggested as a potential food source, but the

average astronaut would have to eat at least 4kg90 of sweet potatoes a day to get enough

protein, so the nutritional benefits of the plant must lie elsewhere. Lactuca sativa, a type of

lettuce currently grown on the ISS, also has a very low amino acid content, with at least 3.7kg

needing to be consumed 91. On Earth, many vegetarians get their protein from beans, these

have a much higher protein content, with Phaseolus vulgaris (the common bean) only

requiring 400g92 to be eaten93(Refer to Table 3 for raw data). Therefore, if space missions

intend to use plants as their main protein source, they should choose a more appropriate

vegetable, such as a bean.

82 NASA, ‘Greenhouses for Mars’ https://science.nasa.gov/science-news/science-at-

nasa/2004/25feb_greenhouses, [accessed 04/04/2017] 83 Daunicht HJ, ‘Plant Responses to Reduced Air Pressure: Advanced Techniques and Results.’, Advances in

Space Research, vol. 18, series 4-5 (1996), pp. 273-281 84 ‘Gravity and More’, https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=gravity, [accessed

29/10/2017] 85 NASA, ‘Vegetable Production System (Veggie) - 11.02.17’,

https://www.nasa.gov/mission_pages/station/research/experiments/383.html, [accessed 25/04/2017] 86 Gioia D. Massa et al., ‘Veg-03 (Veg-03) -10.18.17’

https://www.nasa.gov/mission_pages/station/research/experiments/1294.html, [accessed 02/05/2017] 87 Linda Herridge, ‘Veggie Plant Growth System Activated on International Space Station’

https://www.nasa.gov/content/veggie-plant-growth-system-activated-on-international-space-station [accessed

02/05/2017] 88 NASA, ‘STS-87 Shuttle Mission Imagery’, https://spaceflight.nasa.gov/gallery/images/shuttle/sts-

87/html/s87e5117.html, [accessed 03/12/2017] 89 Markus Czupalla, ‘Life Support System for Pole Station’, Project Boreas: A Station for the Martian

Geographic North Pole, A Publication of The British Interplanetary Society (2006), pp.49-56 90 FAO, ‘Part I, Section I 2. Starchy roots, tubers’

http://www.fao.org/docrep/005/AC854T/AC854T09.htm#chI.I.2 [accessed 02/05/2017] 91 FAO, ‘Part I, Section I 5. Vegetables (continued)’ http://www.fao.org/docrep/005/AC854T/AC854T33.htm

[accessed 02/05/2017] 92 FAO, ‘Part I, Section I 5. Vegetables (continued)’ http://www.fao.org/docrep/005/AC854T/AC854T28.htm

[accessed 02/05/2017] 93 Refer to Appendix A for calculations

11

Table 3: The Amount of Each Essential Amino Acid Within Three Different Species of

Plant94, 95

Plant

species

Amount of amino acid mg/ 100g of food

Histidine Isoleucine Leucine Phenylalanine Lysine Threonine Tryptophan Valine Methionine

Ipomoea batatas

18 48 71 51 45 50 - 59 22

Lactuca

sativa

21 50 83 67 50 54 - 71 24

Phaseolus

vulgaris

627 927 1685 422 1593 878 - 1016 234

Having plants aboard the station would not only be a source of protein but it would also

provide other advantages, for example it could be used as a mental health resource for the

crew96, and it could provide extra oxygen for the station. Therefore, they may still be useful

within the life support system, even they are not used for human consumption.

2.2 Algae

Algae are a large group of protoctistians. There are approximately 50000 different species to

choose from, ranging from single celled organisms to giant kelp. They make their habitat

across the globe, in many different climates and conditions97, meaning there is a high

likelihood of finding one suitable for the Martian climate.

Algae are an excellent protein source: they can also reproduce rapidly under the right

conditions98, they contain nonessential as well as essential amino acids, and they have high

lipid content so they are high in energy99, 100. However, algae also would be useful to bring to

Mars even if it isn’t used as a food source, because it can be turned into a bio fuel; it can

purify dirty water, and it can convert the carbon dioxide in the atmosphere into oxygen which

can be used by the inhabitants of the station.101

Algae are also known to purify water in several different ways, the most notable being that

they can clear heavy metal contaminants102. Therefore, it is highly likely that they would be

able to use the defrosted water from the lake, potentially even if it wasn’t purified

beforehand.

94 Refer to Appendix A for calculations 95 FAO, ‘AMINO-ACID CONTENT OF FOODS AND BIOLOGICAL DATA ON PROTEINS’

http://www.fao.org/docrep/005/AC854T/AC854T00.htm [accessed 02/05/2017] 96 Anna Heiney, ‘Farming in ‘Martian Gardens’, https://www.nasa.gov/feature/farming-in-martian-gardens,

[accessed 28/04/17] 97 Ralph Lewin, ‘Algae’, https://www.britannica.com/science/algae, [accessed 12/07/2017] 98 Algae biomass organisation, ‘Algae Basics’ http://allaboutalgae.com/algae-cultivation/ [accessed 12/07/2017] 99 Van Thang Duong et al., ‘High Protein- and High Lipid-Producing Microalgae from Northern Australia as

Potential Feedstock for Animal Feed and Biodiesel’ Frontiers in Bioengineering and Biotechnology, vol.3

(2015), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4435038/, [accessed 12/07/2017] 100 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’ Biotechnologie,

Agronomie, Société et Environnement/Biotechnology, Agronomy, Society and Environment, vol. 20, series 3

(2016), pp. 427-436 101Algae biomass organisation, ‘Algae Basics’ http://allaboutalgae.com/what-are-algae/[accessed 12/07/2017] 102N. Abdel-Raouf et al., ‘Microalgae and Wastewater Treatment’, Saudi Journal of Biological Sciences, vol.

19, Issue 3 (2012), pp. 257–275

12

Due to the wide range in the group, this report only explores a few species. Published data

shows that algae species can have anywhere between 5.6% and 57% protein103, 104, though

only the top three species, which also had enough data are fully analysed. The best species

found was Dunaliella salina, which only required 100g to meet all the requirements (Refer to

Table 4 for raw data)105, 106, 107. This particular species is very tolerant of varied conditions,

including pH, temperature and salinity108, 109, meaning it wouldn’t be difficult to create

necessary conditions. On Earth, it can be found in salty lakes, which it turns pink, such Lake

Hillier, Australia, shown in Figure 2110.

Table 4: The Amount of Each Essential Amino Acid Within Three Different Species of

Algae 111, 112, 113

Algae

species

Amount of amino acid g/ 100g of protein

Histidine Isoleucine Leucine Phenylalanine Lysine Threonine Tryptophan Valine Methionine

Dunaliel

la salina

2.5 4.5 9.3 6.0 6.2 5.0 - 6.0 2.5

Scenede

smus

obliquus

2.1 3.6 7.3 4.8 5.6 5.1 0.3 6.0 1.5

Cryptopl

eura

ruprechtiana

0.773 0.880 1.450 1.192 2.300 1.304 0.290 1.316 0.415

103 FAO, ‘Part I, Section I 11. Yeast and algae’, http://www.fao.org/docrep/005/AC854T/AC854T55.htm,

[accessed 02/05/2017] 104 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436 105 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science, vol.3 (2014),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017] 106 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436 107 Refer to Appendix A for calculation 108 L. J. Borowitzka et al., ‘The Mass Culture of Dunaliella Salina for Fine Chemicals: From Laboratory to Pilot

Plant’, Hydrobiologia, vol. 116-117, Issue 1 (1984), pp.115-121 109 Michael A. Borowitzka, ‘THE MASS CULTURE OF DUNALIELLA SALINA’,

http://www.fao.org/docrep/field/003/AB728E/AB728E06.htm, [accessed 12/07/2017] 110 Bethany Kolody, ‘Dunaliella salina: the alga that’s always pretty in pink’,

https://algaeresearchsupply.com/pages/dundunaliella-salina-the-algae-that-s-always-pretty-in-pink, [accessed

19/11/2017] 111 Refer to Appendix A for calculation 112

Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science, vol.3 (2014),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017] 113 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436

13

Figure 2: Lake Hillier, Australia 114

In conclusion, algae would make an excellent protein source, they can purify water, produce

oxygen, and they are high in protein. They can also survive in a wide range of habitats,

meaning they can adapt to the Martian environment.

2.3 Cyanobacteria

Cyanobacteria (or blue/green algae) are some of the most ancient organisms known to man. It

is thought that they oxygenated the Earth, making it habitable for all of today’s life115, 116, 117,

and so could do the same for Mars.

Cyanobacteria are often mistaken for algae, but algae are usually eukaryotes, and

cyanobacteria are often unicellular prokaryotes, which means they generally reproduce at a

faster rate118. This rapid reproduction means that they can be genetically engineered to

produce other substances rapidly, which could be useful for generating chemicals such as

medicines on Mars.

114 Bethany Kolody, ‘Dunaliella salina: the alga that’s always pretty in pink’,

https://algaeresearchsupply.com/pages/dundunaliella-salina-the-algae-that-s-always-pretty-in-pink, [accessed

19/11/2017] 115 UCMP, ‘Introduction to the Cyanobacteria’, http://www.ucmp.berkeley.edu/bacteria/cyanointro.html,

[accessed 19/11/2017] 116 Spencer Diamond et al., ‘Cyanobacteria: Growing a Green Future Around the Clock’,

http://schaechter.asmblog.org/schaechter/2011/04/cyanobacteria-growing-a-green-future-around-the-clock.html,

[accessed 12/09/2017] 117 Scott Milroy et al., ‘Pioneering Mars: Turning the Red Planet Green with Earth's Smallest Settlers

(Pioneering Mars) - 07.29.14’, https://www.nasa.gov/mission_pages/station/research/experiments/1188.html,

[accessed 12/07/2017] 118 Spencer Diamond et al., ‘Cyanobacteria: Growing a Green Future Around the Clock’,

http://schaechter.asmblog.org/schaechter/2011/04/cyanobacteria-growing-a-green-future-around-the-clock.html,

[accessed 12/09/2017]

14

They are also known for their nitrogen fixing properties119, so they could fix some of the

small fraction of nitrogen in the atmosphere (1.89%) into ammonia for use120. On Earth, this

process is limited by lack of iron121, but on Mars iron is more abundant122 and so the process

could occur faster. Other bacteria within the nitrogen cycle would be necessary to recycle

nitrogen back into the atmosphere.

This report only assesses one species of cyanobacteria, Arthrospira platensis (Spirulina),

because in “Project Boreas”123 it ranks the highest in “food supply” and “atmosphere

revitalisation”124 two factors which are highly beneficial when travelling to Mars. The other

cyanobacteria analysed had anywhere between 43% and 62% protein content, Spirulina has

roughly 60% to 71% protein, which is a very impressive amount125. To satisfy all the amino

acid requirements the astronaut must consume only 200g of Spirulina (Refer to Table 4 for

raw data) 126, 127.

Table 4: The Amount of Each Essential Amino Acid Within Arthrospira platensis 128, 129

Cyanob

acteria

species

Amount of amino acid mg/ 3g of food

Histidine Isoleucine Leucine Phenylalanine Lysine Threonine Tryptophan Valine Methionine

Arthrosp

ira platensis

15.0 32.6 48.9 26.1 26.2 26.1 8.5 37.4 13.3

There are many ways of growing Spirulina, but all it fundamentally needs is a water

container, water, a little oxygen, carbon dioxide, light, temperature regulation, stirring and

different minerals130, 131. Spirulina currently grows best in warmer temperatures132, though it

may be possible to genetically modify it or find a similar species that can survive the cold

temperatures.

119 M A Saito et al., ‘Iron Conservation by Reduction of Metalloenzyme Inventories in the Marine diazotroph

Crocosphaera watsonii’, Proceedings of the National Academy of Sciences, vol. 108, Issue 6 (2011), pp.2184-

2189 120 NASA, ‘Composition’, https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=composition, [accessed

28/04/2017] 121 M A Saito et al., ‘Iron Conservation by Reduction of Metalloenzyme Inventories in the Marine diazotroph

Crocosphaera watsonii’, Proceedings of the National Academy of Sciences, vol. 108, Issue 6 (2011), pp.2184-

2189 122 NASA, ‘Composition’, https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=composition, [accessed

28/04/2017] 123 Markus Czupalla, ‘Life Support System for Pole Station’, Project Boreas: A Station for the Martian

Geographic North Pole, A Publication of The British Interplanetary Society (2006), pp.49-56 124 Markus Czupalla, ‘Life Support System for Pole Station’, Project Boreas: A Station for the Martian

Geographic North Pole, A Publication of The British Interplanetary Society (2006), pp.49-56 125 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’ pp. 427-436 126 Refer to Appendix A for calculation 127 Micro organics UK ‘Spirulina Nutrient Analysis’ http://www.microrganics-

uk.com/spirulina_nutrient_analysis.htm [accessed 12/07/2017] 128 Micro organics UK ‘Spirulina Nutrient Analysis’ http://www.microrganics-

uk.com/spirulina_nutrient_analysis.htm [accessed 12/07/2017] 129 Refer to Appendix A for calculation 130 The availability of these resources is discussed in section 1.5. 131 Spirulina Academy, ‘Grow Spirulina at Home!’, http://www.spirulinaacademy.com/grow-your-own-

spirulina/ [accessed 12/07/2017] 132 Spirulina Academy, ‘Grow Spirulina at Home!’, http://www.spirulinaacademy.com/grow-your-own-

spirulina/ [accessed 12/07/2017]

15

In conclusion, cyanobacteria are an excellent solution to the protein problem, it’s sustainable

because it can photosynthesise, it doesn’t need much regulation once set up and it contains an

impressive amount of protein.

2.4 Lichen

Lichen is symbiotic relationship between fungi, algae and cyanobacteria. The main benefit of

this is that the photosynthesising part of the relationship makes energy for the non-

photosynthesising part to make amino acids and other useful substances133; this means it

would be more sustainable than fungi alone.

Currently only a few species of lichen are eaten 134, there is no accessible data on the amino

acid content of these specific species, though data was found on 4 species of the same genus.

This isn’t enough information to give a successful conclusion, but it gives an idea of how

much might be required. There was also no sufficient data to consider histidine, methionine,

phenylalanine or tryptophan (and in some cases lysine). Therefore, a minimum of 52200g is

enough to sustain the average astronaut for 1 day (Refer to Table 5 for raw data)135, 136. This

is by far the largest mass to be required by any protein source, so consuming these types of

lichen is unrealistic. The edible species may have a higher protein content so acquiring data

on these would be necessary before completely dismissing lichen as a protein source.

Table 5: The Amount of Each Essential Amino Acid Within Four different Species of

Lichen 137, 138

Lichen

species

Amount of amino acid µ mol/100g of food

Histidine Isoleucine Leucine Phenylalanine Lysine Threonine Tryptophan Valine Methionine

Umbilicaria

carolini

ana

- 2.4 6 - - 8 trace 63.6 -

Parmeli

a incurva

- 4.6 4.6 - - 11.7 - 10.2 -

Cladoni

a

alpetris

- 4.5 13.3 - 9.8 19.3 - 12.3 Trace

Cetraria

delisei

trace 9.8 39.3 trace 20.1 32.5 trace 30.9 Trace

133

The British Lichen Society, ‘What is a Lichen?’ http://www.britishlichensociety.org.uk/about-lichens/what-

is-a-lichen [accessed: 21/07/2017] 134 Bradford Angier, Field Guide to Edible Wild Plants (Stackpole Books, 10/04/2008) p. Iceland moss, Irish

moss, https://books.google.co.uk/books?id=Nq-

3DAAAQBAJ&pg=PT130&lpg=PT130&dq=edible+lichen&source=bl&ots=5-ZdM358uW&sig=_NR-

3j2JwG-0EjkM-exBCafDRVQ&hl=en&sa=X&ved=0ahUKEwjGh-

3QzKnVAhVsJcAKHQdBB8sQ6AEIpgEwGQ#v=onepage&q=edible%20lichen&f=false [accessed

21/07/2017] 135 Fukujiro Fujikawa et al., ‘On Free Amino Acids in Lichens of Japan III’ Pharmaceutical Society of Japan

vol.93 series 12 (1973) pp.1558-1563 136 See Appendix A for calculation 137 Ibid. 138 Fukujiro Fujikawa et al., ‘On Free Amino Acids in Lichens of Japan III’, pp.1558-1563

16

One might think lichen would be a good alternative protein source, because they can

photosynthesise. However, the reality is that the species analysed just don’t produce enough

protein. More research needs to be done to find the exact amino acid content of the edible

species to reach a satisfactory conclusion.

3.0 Fungi

There are 4 types of fungi which are assessed in this report: large mushroom bearing fungi,

mycoprotein, yeasts and moulds. These fungi are analysed because they are the most

commonly eaten here on Earth.

Fungi do not photosynthesise; they get their energy from the substance they are growing on,

and can often be found on dead animals and plant matter for this very reason139, 140, 141, 142, 143.

It would be possible, yet unsustainable to use human waste for this, because of the energy

wastage.

3.1 Large Mushroom-bearing Fungi

For optimal growth, larger fungi require moist conditions144, 145, which means much of the

lake needs to be melted to keep them alive, thus using a large amount of energy. Many

species grow better in hot conditions (though this varies)146, 147 and would need to be heated,

which uses yet more energy. Moreover, there isn’t a very high yield for the input because

mushrooms are only approximately 3% protein 148.

There does not seem to be much research into the amino acid content of mushrooms, so the

analysis is only based on a single study of a single species: Pleurotus ostreatus otherwise

known as the Oyster Mushroom. Each astronaut needs to consume 2500g of Pleurotus

mushrooms a day if that is their only source of protein, which is an unrealistic amount (Refer

to Table 6 for raw data) 149, 150.

139 Heino Lepp, ‘The mycelium’, https://www.anbg.gov.au/fungi/mycelium.html, [accessed 27/07/2017] 140 Mold and Bacteria Facts, ‘What are Fungi?’, http://www.moldbacteriafacts.com/what-are-fungi/, [accessed

03/07/17] 141 Brittanica, ‘Nutrition’, https://www.britannica.com/science/fungus/Nutrition, [accessed 03/07/2017] 142 George Wong, ‘Fungal Diversity (Continued)’,

http://www.botany.hawaii.edu/faculty/wong/BOT135/Lect03_c.htm, [accessed 03/07/2017] 143 Quantum Health Human Research Institute, ‘GENERAL CHEMISTRY OF MEDICINAL MUSHROOMS’,

http://pegasusbp.org/id71.html, [accessed 03/07/2017] 144 Freshmushrooms, ‘Growing Mushrooms’, http://www.mushroominfo.com/growing-mushrooms/, [accessed

03/07/2017] 145 ‘Fungal Diversity (Continued)’, http://www.botany.hawaii.edu/faculty/wong/BOT135/Lect03_c.htm,

[accessed 03/07/2017] 146 Ibid. 147 Freshmushrooms, ‘Growing Mushrooms’, http://www.mushroominfo.com/growing-mushrooms/, [accessed

03/07/2017] 148 Zakia Bano et al., ‘Amino Acid Composition of the Protein from a Mushroom (Pleurotus sp.)’ Applied and

Environmental Microbiology, vol.11, no.3 (1963), pp. 184-187 149 See Appendix A for calculation 150 Zakia Bano et al., ‘Amino Acid Composition of the Protein from a Mushroom (Pleurotus sp.)’, pp. 184-187

17

Table 6: The Amount of Each Essential Amino Acid Within Pleurotus ostreatus

Protein151, 152

Fungi

species

Amount of amino acid g/ 100g of protein

Histidine Isoleucine Leucine Phenylalanine Lysine Threonine Tryptophan Valine Methionine

Pleurotus ostreatus

2.1 5.8 4.4 2.0 5.0 4.2 0.9 4.65 1.26

This data is somewhat unreliable, because there was only one study on it, and it considers

only one species of fungus, therefore further research is required to completely disregard

using fungi as a protein source. However, because they don’t get their energy from the sun,

they are less sustainable than plants, and such a large amount of them must be consumed for a

sizable energy input. Therefore, mushrooms are not the best solution to the problem and an

alternative protein source should be found.

3.2 Mycoprotein

With the popularisation of vegetarianism, the industry for alternative meat products is

becoming more prosperous. Mycoproteins, made from a fungus called Fusarium venenatum,

commercially known as “Quorn” have become a popular protein source for many vegetarians

in the western world. 400g of mycoprotein must be eaten a day to satisfy all of the daily

requirements, and 200g with methionine tablets, which is less than some of the other protein

sources (refer to Table 7 for raw data)153, 154. Mycoprotein is said to be “high in fibre”155

which could be seen as an advantage, because it would aid digestion, but also a disadvantage,

because energy put in to make those fibres hasn’t been absorbed by the human and so could

be seen as a waste.

Table 7: The Amount of Each Essential Amino Acid Within Fusarium venenatum

Protein156, 157

Fungi

species

Amount of amino acid g/ 100g of food

Histidine Isoleucine Leucine Phenyl

alanine

Lysine Threonine Tryptophan Valine Methionine

Fusarium venenatum

0.39 0.57 0.95 0.54 0.91 0.61 0.18 0.60 0.23

Fusarium venenatum requires oxygen, water, temperature regulation, glucose and other

nutrients. The availability of these resources is discussed in section 1.5.

Mycoprotein is a possible protein source for Mars, because it has a large protein content,

doesn’t waste energy by movement, and can feed off waste glucose. However, some of the

other sources contain more protein and can produce their energy from the sun, which is more

sustainable.

151 Ibid. 152 See Appendix A for calculation 153 Refer to Appendix A for calculation 154 Marlow Foods Ltd, ‘Information Sheet for A-Level Home Economics Quorn™ and mycoprotein nutrition.’

http://www.mycoprotein.org/assets/ALFT_V2_2.pdf, [accessed: 11/07/2017] 155Marlow Foods Ltd, ‘Quorn Mycoprotein’,

http://www.mycoprotein.org/index.php/what_is_mycoprotein/nutritional_composition.html, [accessed

27/08/2017] 156 Marlow Foods Ltd, ‘Information Sheet for A-Level Home Economics Quorn™ and mycoprotein nutrition.’

http://www.mycoprotein.org/assets/ALFT_V2_2.pdf, [accessed: 11/07/2017] 157 Refer to Appendix A for calculation

18

3.3 Yeast

A microscopic fungus called yeast would also make a good alternative to larger mushrooms,

because 200g of 2 different strains of Saccharomyces cerevisiae158 (with the exception of

tryptophan in both strains because there is no data) is enough to satisfy all the daily needs

(refer to Table 8 for raw data)159, 160. This is mostly due to the fact that yeast cells are at least

50% protein161.

Table 8: The Amount of Each Essential Amino Acid Nitrogen Within Two Different

Strains of Saccharomyces cerevisiae 162, 163

Fungi

strain

Grams of amino acid nitrogen / 100g of total nitrogen in the yeast

Histidine Isoleucin

e

Leucine Phenylalanine Lysine Threonine Tryptophan Valine Methionine

Baker’s

Yeast

7 3 5 3 8 4 - 7 0.83

Brewer’s

Yeast

7 3 5 1 8 6 - 7 0.81

Yeast would be a good organism to take to Mars, because it can be dried for transportation,

doesn’t require much heavy equipment and in just 2 to 3 days a single yeast cell can produce

up to 100 million new yeast cells through asexual reproduction164, 165, this means that not

many cells need to be brought in the first place. It also contains nonessential amino acids 166.

There are approximately 1500 species of yeasts167, which will all have different requirements,

so more analysis would need to be done to select the best one. Fundamentally though, yeast

requires water, glucose, oxygen, (these resources are discussed in section 1.5) and a variety of

nutrients including a nitrogen source such as a dissolved compound of ammonia, or urea. The

atmosphere of Mars contains a small amount of ammonia168, so it would be possible to

extract it and make it into a compound to dissolve. However, it would be more sustainable to

import bacteria necessary within the nitrogen cycle.

The main disadvantage of yeast is that it doesn’t photosynthesise, so there is no fresh energy

input to the system, this means it cannot be fully sustainable and would only work long term

alongside plants or algae, having an extra layer in the food chain also wastes some energy,

although yeast doesn’t move much, so not much energy would be wasted through movement.

158 O. Lindan et al.,’ The Amino-Acid Composition of Two Yeasts Used to Produce Massive Dietetic Liver

Necrosis in Rats’, Biochemical Journal, vol.48, Issue. 3(1951), pp.337-344 159Refer to Appendix A for calculation 160 O. Lindan et al., ‘The Amino-Acid Composition of Two Yeasts Used to Produce Massive Dietetic Liver

Necrosis in Rats’, pp.337-344 161 Britannica, ‘Yeast’, https://www.britannica.com/science/yeast-fungus, [accessed 03/07/2017] 162 O. Lindan et al., ‘The Amino-Acid Composition of Two Yeasts Used to Produce Massive Dietetic Liver

Necrosis in Rats’, pp.337-344 163 Refer to Appendix A for calculation 164 Yeast Experiments, ‘Baker's Yeast and Its Life Cycle’, https://www.phys.ksu.edu/gene/a1.html, [accessed

13/07/2017] 165 Britannica, ‘Yeast’, https://www.britannica.com/science/yeast-fungus, [accessed 03/07/2017] 166Yeast Experiments, ‘Baker's Yeast and Its Life Cycle’, https://www.phys.ksu.edu/gene/a1.html, [accessed 13/07/2017] 167 Britannica, ‘Yeast’, https://www.britannica.com/science/yeast-fungus, [accessed 03/07/2017] 168 BBC News, ‘Ammonia on Mars could mean life’, http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm, [accessed

13/07/2017]

19

3.4 Mould

Mould is a very similar organism to yeast, with the main difference being that mould tends to

be multi cellular whereas yeast is a single celled organism. The main problem with mould is

that many species release toxins when consumed169, so it is important to choose the right

species so that the astronauts don’t fall ill 170.

The 4 types of mould covered in this report met all the amino acid requirements with 200g

and only 100g with methionine tablets (refer to Table 9 for raw data)171, 172, 173. Two of the

analysed moulds are of the same genus as Fusarium venenatum, however, these are both

parthenogenic fungi174, 175, 176 and are considered inedible. Aspergillus niger is also

inedible177, but there are many different species of mould to choose from, (and with so many

mutant individuals) so there is a high chance of finding one with a similar amino acid content

that is edible.

Table 9: The Amount of Each Essential Amino Acid Within the Mycelia of Four

Different Types of Mould 178, 179

Fungi

species

(and

type)

Amount of amino acid in µmol/ 100mg of food

Histidine Isoleucine Leucine Phenyl alanine

Lysine Threonine Tryptophan Valine Methionine

Aspergillus niger

(wild)

4.72 9.90 15.68 7.95 13.90 12.48 3.18 15.00 3.78

Aspergil

lus niger (mutant

70)

4.32 9.85 15.68 8.30 15.58 12.12 2.89 15.08 3.00

Fusarium

oxyspor

um

5.45 15.02 24.65 10.60 20.55 18.48 3.92 20.40 5.00

Fusarium

monilifo

rme

5.80 13.70 22.20 9.70 21.05 17.90 4.60 20.20 4.92

169 BCC News, ‘How safe is mouldy food to eat?’, http://www.bbc.co.uk/news/magazine-29701768, [accessed

29/09/2017] 170 The Guardian, ‘Spoilt rotten: good and bad mould’,

https://www.theguardian.com/lifeandstyle/2011/oct/26/food-mould-safe-or-toxic [accessed 27/07/2017] 171 Refer to Appendix A for calculation 172 C. Christias et al, ‘Protein Content and Amino Acid Composition of Certain Fungi Evaluated for Microbial

Protein Production’, Applied Microbiology, vol.29, Issue 2 (1975), pp. 250–254 173 Promega, ‘Amino Acids’, https://www.promega.com/-/media/files/resources/technical-references/amino-

acid-abbreviations-and-molecular-weights.pdf [accessed 27/07/2017] 174 Nelson PE, ‘Taxonomy and Biology of Fusarium moniliforme’, Mycopathologia, vol. 117, Issue 1-2 (1992),

pp. 29-36 175 EOL, ‘Fusarium oxysporum’, http://eol.org/pages/187980/hierarchy_entries/57331216/overview, [accessed

16/11/2017] 176 S. Bentley et al., ‘Genetic variation among a world-wide collection of isolates of Fusarium oxysporum f. sp.

cubense analysed by RAPD-PCR fingerprinting’, Mycological Research, vol.99, Issue 11 (1998), pp.1378-1384 177EOL, ‘Aspergillus niger’, http://eol.org/pages/2920814/details, [accessed 27/07/2017] 178 C. Christias et al, ‘Protein Content and Amino Acid Composition of Certain Fungi Evaluated for Microbial

Protein Production’, Applied Microbiology, vol.29, Issue 2 (1975), pp. 250–254 179 Refer to Appendix A for Calculation

20

Mould is a highly resilient organism which can be found all over the world180, and it

also grows very quickly when given the right nutrients, but even though it has a high protein

content, it would still require a photosynthesising body to make it sustainable.

In conclusion, fungi will never be a fully sustainable protein source because they cannot

photosynthesise. It could be worth considering lichen as a potential protein source because it

can photosynthesise and produce amino acids. Of the Fungi assessed mould and yeast have

the least mass that the astronaut would have to eat and they use relatively few resources.

However, other protein sources are much more efficient and so I would recommend looking

elsewhere for the solution.

4.0 Animals

4.1 Vertebrates

Animal181 meat is one of the main sources of protein for many people in the western world.

Its common use on Earth may serve as a comfort to the astronauts when they are away from

home, though it would be very difficult to make in such a hostile environment such as Mars.

As well as mental health benefits, there are a few other advantages to having animals on Mars

(other than for food), heat is a by-product of respiration, which could be used to warmth

against Mars’ cold temperatures, and methane and other waste products they produce could

be used as bio fuel for various uses in the settlement.

One of the problems with using animals is that it wastes energy between trophic levels in

movement, excrement, heat and other bodily processes, which could be saved by humans

eating the plants directly. Animals also require large amounts of oxygen and water in order to

survive which could be difficult to find in the harsh environment Mars has to offer.

Animals also require a lot of food; a “feed conversion ratio”182 can be calculated, using

Equation 2183, to assess the meat yield of different animals for the amount of feed input.

According to the World Resources Institute, eggs contain the most calories and protein for a

set amount of feed input (see Figure 3)184. The benefit of bringing a bird is that the astronauts

can also eat it when it stops producing eggs to use the extra protein.

Equation 2185

180 EOL, ‘Aspergillus niger’, http://eol.org/pages/2920814/details, [accessed 27/07/2017] 181 References to “Animals” in this section refer to “higher animals”, such as vertebrates 182 A well-fed world, ‘Feed:Meat Ratios’, http://awfw.org/feed-ratios/, [accessed 04/07/2017] 183 ‘Aquatic Animal Nutrition: Understanding Feed Conversion Ratios’,

http://www.irrec.ifas.ufl.edu/teachaquaculture/curriculum/_files/modules/6_nutrition/Activity/aquatic_animal_n

utrition-understanding_feed_conversion_ratio.pdf, [accessed 04/07/2017] 184 World Resources Institute, ‘Creating a Sustainable Food Future’,

http://www.wri.org/sites/default/files/wri13_report_4c_wrr_online.pdf, [accessed 04/07/2017] 185 Indian River Research and Education Center, ‘Aquatic Animal Nutrition: Understanding Feed Conversion

Ratios’,

http://www.irrec.ifas.ufl.edu/teachaquaculture/curriculum/_files/modules/6_nutrition/Activity/aquatic_animal_n

utrition-understanding_feed_conversion_ratio.pdf, [accessed 04/07/2017]

21

Figure 3: Input and Output Energies for Common Animal-Derived Foods186

More analysis needs to be done to determine which bird is most appropriate for the task, but a

standard chicken egg will be used in this report. 187

Table 10: The Amount of Each Essential Amino Acid Within Six Proteins in a Chicken

Egg 188, 189

Amino acid Amount of Amino Acid in Each type of Egg protein in g/100g Protein

Lysozyme Conalbumin Ovomucoid Avidin Phoavitin Vitellin

Histidine 1.04 2.57 2.15 0.96 4.8 3.0

Isoleucine 5.2 5.0 1.43 5.5 0.5 5.3

Leucine 6.9 8.8 5.1 4.9 1.0 8.6

Lysine 5.7 10.0 6.0 6.2 5.9 5.9

Phenylalanine 3.12 5.7 2.91 5.9 0.6 0.4

Threonine 5.5 5.9 5.5 10.5 1.4 4.7

Tryptophan 10.6 3.0 0.3 5.4 0.6 1.1

Valine 4.8 8.2 6.6 4.2 1.1 6.2

Methionine 2.06 2.03 0.95 1.41 0.3 2.8

With the exception of Methionine and Phenylalanine, all of the requirements can be met with

just 3 eggs, however to satisfy the need for Methionine the average astronaut has to eat 8 eggs

a day (approximately 500g of egg, raw data shown in Table 10)190, 191, if that is their only

source of protein.

186 World Resources Institute, ‘Creating a Sustainable Food Future’,

http://www.wri.org/sites/default/files/wri13_report_4c_wrr_online.pdf, [accessed 04/07/2017] 187 University of Illinois Extension Incubation and Embryology, ‘Structure of the Egg’,

https://extension.illinois.edu/eggs/res16-egg.html, [accessed 04/07/2017] 188 Refer to Appendix A for calculation 189 J C Lewis et al., ‘AMINO ACID COMPOSITION OF EGG PROTEINS’, Journal of Biological Chemistry,

vol.186 (1950), pp.23-35 190 J C Lewis et al., ‘AMINO ACID COMPOSITION OF EGG PROTEINS’, pp.23-35 191 Refer to Appendix A for calculation

22

Chickens lay roughly 1 egg a day each, but at least 9 chickens should be taken per astronaut

to allow for a failure. Each chicken needs roughly 120g of feed every day 192 which scales up

to 394.2kg of feed to supply enough protein through eggs to an astronaut for 1 Earth year.

This can be reduced, if methionine is taken in pill form, but this is still a very large amount of

mass which doesn’t include the mass of any live chickens, incubation technology or nesting

material. The feed has to be brought on the spacecraft unless an autotroph is grown on Mars,

in which case it would be more efficient to consume that directly.

In conclusion, if an animal were to be brought to Mars as a source of protein, then it would be

some form of bird, because of the high protein content of eggs. However, many resources

would need to be brought from Earth to ensure the survival of the bird, including feed, which

may as well be eaten directly by humans. Unlike plants, the use of animals alone is

unsustainable, because they don’t produce their own nutrients. One could also argue that

bringing an animal on a long space mission is unethical, because the conditions would be too

stressful and cramped.

4.2 Invertebrates

It tends to be a pattern that the smaller an organism is, the larger its feed conversion ratio.

With this in mind, it is logical to explore edible invertebrates as a potential protein source.

Invertebrates have similar problems to vertebrates, though because of their small body mass,

less energy is wasted. Invertebrates also require a lower quality food source for themselves,

and so can use more of the waste products humans provide.

Furthermore, many invertebrates are ectotherms, meaning they don’t waste any energy

maintaining their body temperature. However, this also means they are more vulnerable to

harsh climates, such as the one on Mars, and so would need heating.

There are many phylums and species of invertebrate, this report covers insects, worms and

molluscs, because these are more traditionally eaten on Earth. However, there are many

categories left unexplored, such as sponges, which may be worth looking in to.

4.2.1 Molluscs

Published information on the amino acid content of molluscs is only available for four

species of molluscs 193, and of these the oyster seemed to be the most promising, because the

others were lacking in certain essential amino acids. 9.41%194of an oyster is protein, which is

a surprisingly large amount. The average astronaut has to consume 500g of oyster meat (see

Table 11 for raw data)195, 196 a day to get all the essential amino acids.

192 Omlet, ‘Feeding And Watering Your Chickens’,

https://www.omlet.co.uk/guide/chickens/chicken_care/feeding/, [accessed 04/07/2017] 193De-Wei Chen et al., ‘Amino Acid Profiles of Bivalve Mollusks from Beibu Gulf, China’, Journal of Aquatic

Food Product Technology, Vol.21, Issue 4 (2012), pp.369-379 194 K K Asha et al., ‘Biochemical Profile of Oyster Crassostrea Madrasensis and its Nutritional Attributes’, The

Egyptian Journal of Aquatic Research, Vol.40, Issue 1 (2014), pp.35-41 195 Refer to Appendix A for calculation 196 K K Asha et al., ‘Biochemical Profile of Oyster Crassostrea Madrasensis and its Nutritional Attributes’,

pp.35-41

23

Table 11: The Amount of Each Essential Amino Acid Within Crassostrea madrasensis 197, 198

Oyster

species

Amount of amino acid g/ 100g of crude protein

Histidine Isoleucine Leucine Phenyl

alanine

Lysine Threonine Tryptophan Valine Methionine

Crassostrea

madrasensis

7.7 4.5 2.0 4.1 14.3 12.3 2.17 2.6 4.7

However, oysters need to consume algae or “phytoplankton” 199, 200, (meaning these also need

to be taken or cultured) energy and nutrients would be wasted in creating the shells which

can’t be eaten (though they could be used in other ways), and they are also roughly 83%

moisture201 (so require a lot of water). Therefore, oysters are not the best organism to take to

Mars, but they are better than some alternatives.

4.2.2 Insects, Larvae and Worms

Approximately 80% of the world’s species are insects202, with many yet to be discovered. In

many countries it has become a staple food source (as shown in Figure 4), with it being much

more environmentally friendly than traditional animal meat. Insects require much less feed

than larger animals for the meat they produce 203, 204; therefore, they would be much more

sustainable. They could also feed on some of the waste products humans produce (though this

would be unsustainable without the input of plants to the system), and on plant matter that

humans can’t digest (so less would be wasted).

Figure 4: “A Variety of Insects for Sale as Street Food in Bangkok, Thailand”205

197 Ibid. 198 Refer to Appendix A for calculation 199 http://www.inahalfshell.com/bivalve-curious-01/ (Accessed: 06/07/17) 200 National Geographic, ‘Oysters’, http://www.nationalgeographic.com/animals/invertebrates/group/oysters/

[accessed 06/07/2017] 201 K K Asha et al., ‘Biochemical Profile of Oyster Crassostrea Madrasensis and its Nutritional Attributes’,

pp.35-41 202 For this segment they will be referred to as “Insects” though worms are not classified as an Arthropod. 203 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017] 204 Anand Jagatia, Louisa Field et al., ‘Should we eat Insects?’, BBC Radio,

http://www.bbc.co.uk/programmes/p04ykfkb, (10/04/2017) 205 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017]

24

Not only this, but between 13% and 77% of an insect is protein 206(which varies with species

and age). Of the five-species analysed (refer to Table 12 for raw data) 207, 208, 209, 2 satisfied

the requirements with just 100g of insects a day. This is a very small amount which needs to

be eaten in comparison to the other sources of protein.

Table 12: The Amount of Each Essential Amino Acid Within Five Species of Insect 210,

211, 212

Insect species

(and types)

Amount of amino acid mg/ g of dry mass

Histidine Iso

leucine

Leucine Phenyl

alanine

Lysine Threonine Tryptophan Valine Methionine

Periplaneta

americana

15.42 18.81 35.86 19.68 34.91 21.01 4.71 30.99 8.90

Sarcophaga

(Neobelliaria) bullata

23.47 27.40 44.86 40.62 56.14 27.15 8.93 35.46 15.96

Pogonomyrmexoc

cidentalis

15.13 30.33 46.92 16.15 28.42 24.36 NA 37.94 8.03

Sarcophaga (Neobelliaria)

bullata

24.88 32.05 51.80 32.37 61.36 29.00 9.00 40.39 19.91

Hermetiaillucens 15.60 17.30 28.75 16.00 28.57 16.54 6.26 26.01 6.94

Tenebrio molitor 15.5 24.7 52.2 17.3 26.8 20.2 3.9 28.9 6.3

The adult Sarcophaga bullata (flesh fly) contained the most essential amino acids, with only

50g satisfying the daily requirements. There is no published information into the edibility of

this particular species, though the vast variety in the insect population means that it is highly

likely that even if it is not edible, there is another similar species that is. More analysis would

need to be done to find the ideal insect to bring to the Martian environment.

In conclusion, the animal kingdom contains a wide variety of organisms which contain a high

level of protein. However, if an animal is to be taken to Mars, further analysis of insects,

worms and larvae should be done, to determine the best species to bring.

5.0 New Protein Sources

5.1 Methanotrophs

This is perhaps the most modern idea of protein production explored in this report, currently

only used as animal feed 213, 214, methane eating bacteria (methanotrophs) may be the future

206 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017] 207 Ibid. 208 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science,

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017] 209 Refer to Appendix A for calculation 210 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017] 211 Refer to Appendix A for Calculation 212 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed

06/07/2017]

25

of protein production. These bacteria, found in freshwater environments, use methane and

nitrogen oxide (or oxygen) to produce ATP and carbon dioxide, this means that only a small

amount of oxygen would be required to make the protein 215, 216, 217, 218, 219, 220, so there is less

competition between humans and bacteria. There are traces of methane and nitrogen oxide in

the Martian atmosphere221, though this would probably not be enough to sustain the

organism. Therefore, these gases would need to come from human waste, or Earth, there may

not be enough of these gases produced to make the system sustainable. Any water and carbon

dioxide they require can be found on Mars.

There is currently no accessible data on the exact amino acid content of the bacteria, though

they are approximately 71% protein222, which is only out performed by some insect species.

Humans can’t currently eat these microorganisms because they contain a high amount of

nucleic acids223, this can be useful to grow new cells, but in too high quantities can have

negative epigenetic effects due to accidental manipulation of the DNA. Too many purines can

also lead to the build-up of gout which is harmful to the astronauts.

Methanotrophs are not currently to be the best solution to the protein problem on Mars.

However, they could be the future of protein production on Earth since they use methane, a

greenhouse gas. More research needs to be done into this exciting new technology if it is to

be used by humans on a larger scale.

5.2 Cultured Meat

Cultured meat is a very new development, so new in fact, that the technologies required to

grow it on a large scale have not yet been developed. In vitro meat is made using myoblast

cells, cells which are in the middle of developing from stem cells to skeletal muscle cells, this

is because stem cells are difficult to differentiate and skeletal muscle cells are difficult to

proliferate quickly (rapidly replicate). The stem cells used to make the myoblast cells can

come from one of two places, and each has its own associated problems. The stem cells could

213 Jodi Helmer, ‘Methane-eating bacteria could reduce the impact of our big appetite for fish’,

https://www.theguardian.com/sustainable-business/2016/mar/17/methane-eating-bacteria-reduce-impact-fish-

demand-feedkind-calysta, [accessed 14/07/2017] 214 Calysta, ‘FeedKind® Protein’, http://calysta.com/feedkind/product/, [accessed 14/07/2017] 215 Margareth Øverland et al., ‘Evaluation of Methane-Utilising Bacteria Products as Feed Ingredients for

Monogastric Animals’, Archives of Animal Nutrition, vol. 64, Issue 3 (2010), pp. 171-189 216 Richard Hansen et al., ‘Methanotrophic Bacteria.’, Microbiological Reviews, Vol. 60, No. 2 (June 1996), p.

439–471 217 Ming Wu et al., ‘XoxF-Type Methanol Dehydrogenase from the Anaerobic Methanotroph “Candidatus

Methylomirabilis oxyfera”’, Applied and Environmental Microbiology,vol. 81, Issue 4 (2014), pp. 1442-1451 218 M. L. Wu et al., ‘Ultrastructure of the Denitrifying Methanotroph "Candidatus Methylomirabilis oxyfera," a

Novel Polygon-Shaped Bacterium’, Journal of Bacteriology, vol.194, Issue 2 (2011), pp.284-291 219 Amanda Leigh Mascarelli, ‘Methane-eating microbes make their own oxygen’,

http://www.nature.com/news/2010/100324/full/news.2010.146.html [accessed 14/07/2017] 220 P. J. Strong et al., ‘Methane as a Resource: Can the Methanotrophs Add Value?’, Environmental Science &

Technology, vol.49, Issue 7 (2015), pp.4001-4018 221 NASA, ‘Mars Fact Sheet’, https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html, [accessed

14/07/2017] 222 Calysta, ‘FeedKind® Protein’, http://calysta.com/feedkind/product/, [accessed 14/07/2017] 223 Margareth Øverland et al., ‘Evaluation of Methane-Utilising Bacteria Products as Feed Ingredients for

Monogastric Animals’, pp. 171-189

26

be taken from the adult animal’s bone marrow. However, this is not sustainable because the

cells can only replicate for some weeks224.

Much of the technology to make large amounts of cultured meat has not yet been developed.

The first thing which is required is a suitable growth and differentiation media; the culture

has no digestive system, which means all the nutrients it requires has to be within the

medium225, 226, and different stages of the cells life required different nutrients, which further

complicates the job. Furthermore, animal products cannot be used in the media, because that

makes the system unsustainable. Another technology which needs to be developed is the

frame on which the culture grows: it needs to have a branched structure with a large surface

area, due to the lack of digestive system, it needs to be flexible to allow the culture to grow

without being obstructed, and any by-products it makes must be edible, in case they end up in

the final product227, 228. It should also be easy to remove the meat from, or it should be

edible229, 230 so crew time isn’t wasted trying to extract it.

Previously in this report, it was discussed how energy can be wasted through movement, but

lack of movement is the problem for cultured meat, because it can get muscle atrophy. This is

a decrease in myosin heavy chain (a protein which makes up thick muscle filament) 231, 232, 233,

234 which causes weak muscles (astronauts often experience this when they are in

microgravity), this would make less meat, and with lower protein content. In order to fix this

problem, a suitable bioreactor would need to be developed that is also light and large enough

to make the necessary protein 121.

As well as the lack of technology, there are also some other disadvantages to bringing in vitro

meat to Mars, the firstly it requires so many resources that other protein sources don’t which

could end up being heavy on the trip there, it also takes several weeks to grow235, longer that

some of the other processes, and it still requires plant resources to live. However, there are

also a few advantages to it, it means that the astronauts can enjoy animal meat (although it is

224 Future Food, ‘CULTURED MEAT; MANUFACTURING OF MEAT PRODUCTS THROUGH "TISSUE-

ENGINEERING" TECHNOLOGY.’,http://www.futurefood.org/in-vitro-meat/index_en.php, [accessed

22/07/2017] 225 Future Food, ‘CULTURED MEAT; MANUFACTURING OF MEAT PRODUCTS THROUGH "TISSUE-

ENGINEERING" TECHNOLOGY.’,http://www.futurefood.org/in-vitro-meat/index_en.php, [accessed

22/07/2017] 226 Zuhaib Fayaz Bhat et al., ‘Prospectus of Cultured Meat—Advancing Meat Alternatives’, Journal of Food

Science and Technology, vol. 48, Issue 2 (2010), pp. 125-140 227 Zuhaib Fayaz Bhat et al., ‘Prospectus of Cultured Meat—Advancing Meat Alternatives’, pp. 125-140 228 Future Food, ‘CULTURED MEAT; MANUFACTURING OF MEAT PRODUCTS THROUGH "TISSUE-

ENGINEERING" TECHNOLOGY.’,http://www.futurefood.org/in-vitro-meat/index_en.php, [accessed

22/07/2017] 229 Ibid. 230 Zuhaib Fayaz Bhat et al., ‘Prospectus of Cultured Meat—Advancing Meat Alternatives’, pp. 125-140 231 Greg Chin, ‘Muscle Contraction: Actin and Myosin Bonding’, http://study.com/academy/lesson/muscle-

contraction-actin-and-myocin-bonding.html, [accessed 20/12/2016] 232 IvyRose Holistic, ‘Structures of Muscle Filaments’,

http://www.ivyroses.com/HumanBody/Muscles/Muscle_Filaments.php, [accessed 20/12/2016] 233 Unilever, ‘Proteins 5. Proteins in structures’, http://resources.schoolscience.co.uk/unilever/16-

18/proteins/Protch5pg3.html, [accessed 20/12/2016] 234 NASA, ‘Effect of Prolonged Space Flight on Human Skeletal Muscle (Biopsy) - 11.22.16’,

https://www.nasa.gov/mission_pages/station/research/experiments/245.html, [accessed 20/12/2016] 235 Zuhaib Fayaz Bhat et al., ‘Prospectus of Cultured Meat—Advancing Meat Alternatives’, pp. 125-140

27

difficult to replicate the imperfections which give animal meat its texture and flavour236),

which could be good for their mental health, without having to put an actual animal through

the stress of space travel. It also doesn’t take up much space on Mars which would leave

much of the landscape free for scientific exploration.

To conclude, without more technology being developed to make this process more efficient,

it currently doesn’t seem much better than bringing live animals. However, because of the

rapid development of technology, it could be a potential solution in the future.

6.0 Bringing food

The last method of protein production explored in this report involves very little or no

preparation on Mars. The main advantage of bringing food to Mars is that a varied diet can be

designed, which isn’t dependent on an external system working, and is designed to the

individual.

However, bringing food is not sustainable because eventually the astronauts would consume

all the food, or the food would spoil (however, food is less likely to spoil because of the lack

of microbes on Mars). This means that the Martian colony would still be dependent on Earth

to send food regularly, unless it was a short-term mission. This approach works on the ISS,

where missions only last approximately 6 months237, though the ISS is much closer to the

Earth, and it is likely that a Mars mission would last longer to justify the cost.

There are different methods of preserving food so that it lasts longer238, 239, 240, 241, 242, 243, it is

logical to bring the protein in the form insects or algae, whichever method of preserving is

used. Facilities on Earth could be used to extract amino acids and put them in tablet form,

which reduces mass.

Taking food may also end up being a similar total mass to other methods because while the

ship is carrying all the food, it is also carrying less equipment, depending on which protein

production method it is being compared to.

A factor which might be considered is the climate impact, because any climate impact would

now occur on Earth and not on Mars, this would be advantageous, because it leaves the

natural climate of Mars to be studied without the contamination of humans.

236 Maeve Henchion et al., ‘Future Protein Supply and Demand: Strategies and Factors Influencing a Sustainable

Equilibrium’, Foods, vol. 6, Issue. 7 (2017), http://www.mdpi.com/2304-8158/6/7/53, [ accessed 22/07/2017] 237 NASA, ‘Astronauts Answer Student Questions’,

https://www.nasa.gov/centers/johnson/pdf/569954main_astronaut%20_FAQ.pdf, [accessed 27/08/2017] 238Eat By Date, ‘How Long do Pickles Last?’ https://www.eatbydate.com/other/condiments/how-long-do-

pickles-last/, [accessed 18/07/2017] 239 Eat By Date, ‘How Long Does Jam/Jelly Last?’, http://www.eatbydate.com/other/condiments/how-long-

does-jam-last-shelf-life-expiration-date/, [accessed 18/07/2017] 240 Food Standards Australia New Zealand, ‘Canned foods: purchasing and storing’,

http://www.foodstandards.gov.au/consumer/safety/cannedfoods/Pages/default.aspx, [accessed 18/07/2017] 241 BBC Bitesize, ‘Food preservation’,

http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/greenworld/decayrev2.shtml,

[accessed 18/07/2017] 242 Food Safety.gov, ‘Storage Times for the Refrigerator and Freezer’,

https://www.foodsafety.gov/keep/charts/storagetimes.html, [accessed 18/07/2017] 243 National Centre for Home Food Preservation, ‘General Freezing Information’,

http://nchfp.uga.edu/how/freeze/freezer_shelf_life.html, [accessed 20/11/2017]

28

In conclusion, bringing food is the best method of protein production for a short, returning

mission lasting around two years244, but in the long term, it isn’t sustainable and therefore

would not be a suitable solution.

7.0 Conclusion

7.1 Assumptions and Flaws in My Assessment

Calculations throughout this report only give an approximate idea of how much of each food

will need to be consumed, to make them comparable to each other. Firstly, figures are

rounded up to the nearest 100g, and so to do a full assessment more degrees of accuracy

would be required.

Where data was only available on selected proteins within the organism, it was assumed that

those proteins made up the total amount of protein in equal proportions, which is not true. It

is frequently assumed that the whole of the body is digestible which means the quantity could

be an underestimate because it doesn’t take wastage into account.

Within the calculations, it was assumed that there is only one source of amino acids, which is

naturally not true in the context of Martian exploration, because a varied diet would be

important to the health of the astronauts.

Due to time constraints, it was impossible to analyse every species of organism on Earth,

therefore only a small sample of species was analysed to represent each kingdom or phylum,

this is inaccurate because most organisms vary enormously from species to species and many

of the species analysed are currently inedible. Therefore, more analysis would need to be

done in order to fully address this question.

The variety of possible protein sources was vast, and so that limited the amount of detail

possible. The research in this report demonstrates which protein sources are most promising,

and some of the resources they require, with more time it would be possible to examine these

few organisms, comparing specific species.

7.2 Conclusion

One of the protein sources which the average astronaut has to eat least of in order to be fully

sustained is insects, which required up to 200g, depending on the species (for one it was only

50g) (as shown in Figure 4 and 5), all of the requirements can be met for 10 days when 1kg 245of insects are consumed. However, insects need a food source themselves, and so the

system wouldn’t be fully sustainable without a photosynthesising organism for them to feed

on.

Of the photosynthesising organisms, algae and cyanobacteria required the least to be

consumed to meet the requirements, between 100 and 300g. The photosynthesising organism

with the number of days where the requirement is met, and therefore that has the lowest mass

244 Food Standards Australia New Zealand, ‘Canned foods: purchasing and storing’,

http://www.foodstandards.gov.au/consumer/safety/cannedfoods/Pages/default.aspx, [accessed 18/07/2017] 245 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science, vol.3 (2014),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017]

29

to be consumed per day, is Dunaliella salina, for which 1kg is 10 days of protein, with 100g

to be consumed each day246, the same as some insects. Whether Dunaliella salina or an insect

is better depends on how much protein and energy is lost between trophic levels. If insects

can digest parts of algae that humans can’t, it may be worth bringing both. With more time

this question could be addressed, as well as more detailed data on which has the lowest daily

requirement.

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Gra

ms

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g)/g

Species

Grams Required to Fulfil the Amino Acid Requirements of the

Average Astronaut per Day (Rounded up to the Nearest 100g)/g (Excluding Lichen)

Figure 4: Mass Required to Fulfil the Amino Acid Requirements of the Average

Astronaut Per Day (Rounded Up to the Nearest 100g)/g (Excluding Lichen) 247, 248, 249, 250,

251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261

246 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436 247 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017]

30

0

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s

Species

Days the Requirement is Met with 1kg of the Protein Source/ days/kg

(Excluding Lichen)

Figure 5: Days the Requirement is Met When 1kg of the Protein Source is Consumed/

Days (Excluding Lichen) 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276

248 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed

06/07/2017] 249 Ibid. 250 J C Lewis et al., ‘AMINO ACID COMPOSITION OF EGG PROTEINS’, Journal of Biological Chemistry,

vol.186 (1950), pp.23-35 251 C. Christias et al, ‘Protein Content and Amino Acid Composition of Certain Fungi Evaluated for Microbial

Protein Production’, Applied Microbiology, vol.29, Issue 2 (1975), pp. 250–254 252 O. Lindan et al., ‘The Amino-Acid Composition of Two Yeasts Used to Produce Massive Dietetic Liver

Necrosis in Rats’, pp.337-344 253 Marlow Foods Ltd, ‘Information Sheet for A-Level Home Economics Quorn™ and mycoprotein nutrition.’

http://www.mycoprotein.org/assets/ALFT_V2_2.pdf, [accessed: 11/07/2017] 254 Ibid. 255 Ibid. 256 Fukujiro Fujikawa et al., ‘On Free Amino Acids in Lichens of Japan III’, pp.1558-1563 257 Micro organics UK ‘Spirulina Nutrient Analysis’ http://www.microrganics-

uk.com/spirulina_nutrient_analysis.htm [accessed 12/07/2017] 258

Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science, vol.3 (2014),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017] 259 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436 260 FAO, ‘AMINO-ACID CONTENT OF FOODS AND BIOLOGICAL DATA ON PROTEINS’

http://www.fao.org/docrep/005/AC854T/AC854T00.htm [accessed 02/05/2017] 261 Refer to Appendix A for calculations 262 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017]

31

Many of the more modern technologies are so new that they have not yet had time to develop

much efficiency, whether it is worth revisiting these or not depends on how far in the future

the Mars mission takes place, and how much the technologies have developed. There is also

not enough available data on their protein content to draw satisfactory comparisons to

currently available protein sources, therefore it is not currently possible to draw conclusions

about their protein content.

Another factor that needs consideration is if this mission is long or short term. Astronauts are

currently sent to the ISS for approximately 6 months277, but the ISS is easier to re-stock than

Mars, because it’s a lot closer to Earth. Restocking food every two years would take up a lot

of energy and resources and it means that the Martian colony would be entirely dependent on

Earth. I think bringing food is the best solution for a short space mission because the

astronauts can customise their food, and the protein content can be carefully controlled.

If the astronauts are to stay on Mars indefinitely, I would recommend bringing insects, algae,

or plants or a combination of the four. Plants are recommended because it is likely that most

insect species will feed on plants, and because the mental health benefits would be vital to the

astronauts. Insects and algae are recommended for their high protein content.

In conclusion, I would look at the nature of the proposed Mars mission, consider the rest of

the diet, and look at the latest development in technology before making the final decision on

which protein source to bring. As of now, insects, algae, plants, bringing food, or a

combination, appear to be the best options.

263 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed

06/07/2017] 264 Ibid. 265 J C Lewis et al., ‘AMINO ACID COMPOSITION OF EGG PROTEINS’, Journal of Biological Chemistry,

vol.186 (1950), pp.23-35 266 C. Christias et al, ‘Protein Content and Amino Acid Composition of Certain Fungi Evaluated for Microbial

Protein Production’, Applied Microbiology, vol.29, Issue 2 (1975), pp. 250–254 267 O. Lindan et al., ‘The Amino-Acid Composition of Two Yeasts Used to Produce Massive Dietetic Liver

Necrosis in Rats’, pp.337-344 268 Marlow Foods Ltd, ‘Information Sheet for A-Level Home Economics Quorn™ and mycoprotein nutrition.’

http://www.mycoprotein.org/assets/ALFT_V2_2.pdf, [accessed: 11/07/2017] 269 Ibid. 270 Ibid. 271 Fukujiro Fujikawa et al., ‘On Free Amino Acids in Lichens of Japan III’, pp.1558-1563 272 Micro organics UK ‘Spirulina Nutrient Analysis’ http://www.microrganics-

uk.com/spirulina_nutrient_analysis.htm [accessed 12/07/2017] 273

Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science, vol.3 (2014),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017] 274 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436 275 FAO, ‘AMINO-ACID CONTENT OF FOODS AND BIOLOGICAL DATA ON PROTEINS’

http://www.fao.org/docrep/005/AC854T/AC854T00.htm [accessed 02/05/2017] 276 Refer to Appendix A for calculations 277 NASA, ‘ Astronauts Answer Student Questions’,

https://www.nasa.gov/centers/johnson/pdf/569954main_astronaut%20_FAQ.pdf [accessed 27/08/2017]

32

Appendix A

Calculations of the mass of food to be consumed by the average astronaut per day to meet the

daily requirements

Protein source Calculations

Plant 278 The data is in mg/100g of food.

1.Convert this into g/100g of food by dividing by 1000.

2.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Algae279 The data is in g/100g protein

Scenedesmus obliquus is 51.5% protein (average)

Dunaliella salina is 57% protein

1. Convert into g/100g food by dividing by 100/ %protein

2.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Algae280 The data is in mg/g dry matter

1.Convert to g/100g by dividing by 10

2.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Cyanobacteria281 The data is in mg/3g of food.

1.Convert this into g/3g by dividing by 1000

2.Convert into g/100g by multiplying by 100/3

3.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Lichen282 The data is in µmol/100g food

1.Convert into µg/100g by multiplying each data point by its

respective molecular mass

2.Convert into g/100g by dividing by 1000000

3.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Large

Mushroom

Bearing Fungi283

The data is in g/ 100g protein.

A mushroom is 2.78 % protein

1.Convert to g/ 100g of food by dividing by 5000/139

2.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Mycoprotein284 The data is in g/100g of food

1.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

278 FAO, ‘AMINO-ACID CONTENT OF FOODS AND BIOLOGICAL DATA ON PROTEINS’

http://www.fao.org/docrep/005/AC854T/AC854T00.htm [accessed 02/05/2017] 279 Abakoura Barka et al., ‘Microalgae as a potential source of single-cell proteins. A review’, pp. 427-436 280Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, Journal of Nutritional Science, vol.3 (2014),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed 06/07/2017] 281 Micro organics UK ‘Spirulina Nutrient Analysis’ http://www.microrganics-

uk.com/spirulina_nutrient_analysis.htm [accessed 12/07/2017] 282 Fukujiro Fujikawa et al., ‘On Free Amino Acids in Lichens of Japan III’, pp.1558-1563 283 Zakia Bano et al., ‘Amino Acid Composition of the Protein from a Mushroom (Pleurotus sp.)’, pp. 184-187 284 Marlow Foods Ltd, ‘Information Sheet for A-Level Home Economics Quorn™ and mycoprotein nutrition.’

http://www.mycoprotein.org/assets/ALFT_V2_2.pdf, [accessed: 11/07/2017]

33

Yeast285 The data is in g of amino acid nitrogen / 100g of total nitrogen in the

yeast

The amount of total nitrogen in 100g of yeast is also given.

A= Mass of amino acid nitrogen

T = Total mass of nitrogen

Y =Total mass of yeast

M = Molecular mass of the amino acid

Subscripts represent the same variables within different ratios

1.Create a ratio of A1: T2:Y in which:

Y is acquired by dividing (100)2 by the T in 100g of yeast (T1).

A1 is given as raw data.

T2 is 100

2.Create a ratio of A2:M

A2 is acquired by calculating the mass of Nitrogen in a single amino

acid

M is the total mass of all the atoms in the amino acid

3. Create a ratio of A3:Y

Y is the same as step 1

A3 is calculated by doing M/(A2/A1)

4. The mass of amino acid in Yg of yeast is now known, convert this

to 100g of yeast. This can be done by multiplying both sides of the

ratio by 100/ T1

5. Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Mould286 The data is in µmol/100mg of food

1.Convert to g/100mg of food by multiplying each data point by its

respective molecular mass

2.Convert to g/100g by dividing by 1000

3.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Animal287 The data is in g/100g of each type of protein

The edible part of an egg is 13% protein

The average mass of an egg is 57g

It is assumed that only the shown proteins make up the proteins in

the egg and that they each take up 1/6th of the total protein, meaning

the result is a very rough approximation.

1.Find the g/600g of mixed protein by adding up all the values for

each amino acid.

2.Convert to g/100g protein by dividing by 6

3. Convert to g/100g food by dividing by 100/13

4. Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

To find the number of eggs required:

Find the mass of protein in a single egg by calculating 13% of 57

285 O. Lindan et al., ‘The Amino-Acid Composition of Two Yeasts Used to Produce Massive Dietetic Liver

Necrosis in Rats’, pp.337-344 286 C. Christias et al, ‘Protein Content and Amino Acid Composition of Certain Fungi Evaluated for Microbial

Protein Production’, Applied Microbiology, vol.29, Issue 2 (1975), pp. 250–254 287 J C Lewis et al., ‘AMINO ACID COMPOSITION OF EGG PROTEINS’, Journal of Biological Chemistry,

vol.186 (1950), pp.23-35

34

which is 7.41g

Multiply the g/600g protein value by 7.41/600, this gives you the

g/egg

3. Use trial and error to find the lowest mass number of eggs which

meets the daily requirement of each amino acid.

Mollusc288 The data is in g/100g Crude Protein, I have assumed that Crude

protein is total protein, meaning the final product is overestimate of

the requirement.

An oyster is 9.41% protein

1.Convert to g/100g food by dividing by 100/9.41

2.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Insect289, 290 The data is in mg/g and g/kg dry mass

1.Convert to g/100g by dividing by 10

2.Use trial and error to find the lowest mass (to the nearest 100g)

which met the daily requirement of each amino acid.

Appendix B

Other Calculations

Product Calculations

Mass of essential amino acid required per

day for an average astronaut (mg) 291

Multiply the requirement in mg/kg/day by

the mass of the astronaut (67kg).

Partial pressure of Carbon dioxide on

Mars by comparison to Earth’s

atmosphere292, 293, 294

7.5 millibars x 95 = 712.5

712.5/100 = 7.1 millibars

1013 millibars x 0.038 = 26657.89474

26657.89474/100 = 0.38 millibars

288 Ibid. 289 FAO, ‘6. nutritional value of insects for human consumption’,

http://www.fao.org/docrep/018/i3253e/i3253e06.pdf, [accessed 06/07/2017] 290 Sarah McCusker et al. ‘Amino acid content of selected plant, algae and insect species: a search for alternative

protein sources for use in pet foods’, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473169/, [accessed

06/07/2017] 291 National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary

Allowances., Recommended Dietary Allowances: 10th Edition., Chapter 6 292 NASA, ‘Composition’ https://mars.nasa.gov/allaboutmars/facts/#?c=theplanet&s=composition, [accessed

28/04/2017] 293 Jerry Coffey, ‘Air on Mars’, https://www.universetoday.com/14872/air-on-mars/, [accessed 04/04/2017] 294 PHOENIX MARS MISSION, NASA, ‘Mars/Earth Comparison Table’,

http://phoenix.lpl.arizona.edu/mars111.php, [accessed 03/12/2017]

35

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