Our First Martian Plants
What plants should we choose to support the first human colonies on the Red Planet?
Plants are awesome. It is astonishing to realize that almost every waste byproduct produced by humans is used by plants in order for them to survive. It is even more baffling that the opposite is also true for plants. Coincidence? I think not!
Every time a human being inhales a breath of our nitrogen-oxygen atmosphere, our bodies absorb the oxygen in order to process the food we eat so that we have energy to survive. Then, we breathe out an equal volume of highly CO2-saturated air back into our biosphere. This CO2 is in turn used by plants, in tandem with photosynthesis, for them to produce the energy they need to grow and reproduce. They secrete oxygen as a byproduct. But plant’s also require nitrogenous nutrients from the ground in order to continue this process, which humans and other animals provide in the form of waste from the food we eat. And where do we get this food? Humans in general get 50% of their nutrients from plants and the other 50% from animal products.
When it comes to building a completely self-sustaining colony on Mars, the usefulness of this symbiotic relationship between plants and humans becomes blatantly obvious. The fact that nature has already devised an efficient process for converting the waste products of humans back into useful forms is an asset that we would not be frugal to ignore. Trying to engineer our own way of dealing with these unwanted byproducts without plants would only increase the complexity and cost of any colonization effort directed towards Mars.
The Idea
Yes, plants are the way to go… but what kind of plants? Every plant on Earth produces oxygen (that is the definition of a plant). But plants come in a nearly infinite variety. There are trees, shrubs, weeds, vines, bushes, grasses, algae; the list propagates nearly into infinity. I was having a conversation the other day with jack, one of my roommates from college, who prompted me with this question. So, naturally, I decided to do some research to see if I could figure out which plant seeds we should start packing up if we want to set up a permanent settlement on the Red Planet.
As was aforementioned, plants are useful to humans in two main respects: their ability to produce oxygen and and their ability to bear food. The first factor is not as trivial as one might expect. Though all plants produce oxygen, they all produce it in different quantities and at different rates. The amount of oxygen produced by a plant is generally determined by it’s photosynthesis producing surface area, or the surface area of the leaves (or needles or whatever). In general, the more green a plant is, the more photosynthesis it performs, and thus the more oxygen said plant produces.
The second quality of our Martian plant is its ability to produce food. A Martian colony will require a large variety of plants in order to support the diverse human diet. Fruits, vegetables, grains, and nuts are all plant based foods which are essential to the human food pyramid, and can provide most of the necessary nutrients to survive. Things like dairy and meat may have to be substituted for other food groups at first until the colony can become more complex.
To perform this thought experiment, I am going to imagine a private company that wishes to establish a permanent settlement on Mars with, oh I don’t know, 100 people. All of these people will need food, oxygen, and water. We already know that Mars has enough water frozen in it’s regolith to provide sustenance for such a human colony, so it all comes down to plants. So, which plants will accompany us on our first manned colonization effort to Mars?
The Requirements
On average, a plant produces oxygen at a rate of 0.05 milliliters per hour per cm² of leaf. A healthy human consumes roughly 50 liters of oxygen per hour. Simple math shows that to address the needs of 100 humans, our settlement will require at least 10,000 square meters of photosynthesis producing surface area to survive. This, however, assumes the same light intensity for the plants that we receive here on Earth. Mars does have a thinner atmosphere which allows a larger percentage of light from the sun to actually reach the surface compared to Earth, but when you factor in the distance, Mars receives just more than 50% the solar energy that the Earth does at it’s surface. This will double our plant surface area needed to 20,000 square meters (this is leaf surface area, NOT ground surface area). This is equivalent to four, full grown oak trees worth of leaves.
When I crunch these same numbers for CO2 waste/extraction, however, I actually found something rather astonishing. For some reason, even though our plants provide enough oxygen for our human colonists, humans only produce about half of the required CO2 for the plants themselves to continue to perform photosynthesis. In short, our current setup actually has twice the number of plants that it can sustain. This will leave our plants CO2 deprived. My theory here is that plants were obviously around before animals, and so they actually evolved to get most of their CO2 from other places (volcanic eruptions, primordial CO2, etc.) and not just from animals. Our plants will require extra CO2 from somewhere. Fortunately, 96% of Mars’s tenuous atmosphere is composed of CO2, so we won’t have a problem extracting some to bring in for our plants.
Finally, humans consume about 2.7 kilograms of food per day which, in our case, will be entirely plant based. This equates to our plants producing ~8100 kg/month (about 100,000 kg/year) of foods of all varieties in order to sustain and nourish our hungry colonists. The food pyramid may need to be altered a bit to account for the lack of dairy and meat, but approximately 50% of this mass needs to be raw greens and vegetables, 30% will be fruits, 10% will be wheat and grains, and 10% will be protein rich nuts, seeds, and beans.
The Solution
Potato plants, apple trees, and tomatoes plants are a great place to start, all having large quantities of photosynthesis producing leaves and high mass food yields. Leafy greens like spinach, broccoli, and kale are also appealing due to the fact that you actually eat the part that performs photosynthesis, so none of the plant’s energy goes into producing a separate fruit/vegetable at all. Rice, though not as efficient at producing oxygen, has an astonishingly high food yield, and can be harvested multiple times per year. For protein, many bean plants have tons of leaves for O2 production, as well as a fairly high food mass yield.
To make things simple, let’s imagine that that the first colony’s food palate is not quite so diverse. We will allow them one fruit, one vegetable, one grain, and one protien nut/bean for their diet in order to survive. Apple trees are a great starting point, being relatively short, high in leaves, and having large fruit production (Though in reality it takes years to grow a fruit producing apple tree, I’m going to assume that they found a way to bring trees with them on the voyage to Mars or have had them planted in advance.) Potatoes seem to be the food powerhouse of for the vegetable kingdom. For grains, rice seems to be the way to go, being easy to harvest and producing a high yield. Finally, soybean plants have the ability to provide a high protein consumable, while offering high levels of O2 production.
Here’s what I found:
Let’s run through this table quick. To support 100 colonists indefinitely on Mars requires nearly 200 apple trees, more than 10,000 potato plants, almost 300,000 rice stalks, and roughly 70,000 soybean plants. It looks like O2 production won’t be a problem, as the combined surface areas of all of our plants greatly outpaces our 20,000 square meter required surface area. Some of these numbers look really high, like the number of rice stalks, but also remember that rice stalks are skinny and space efficient, and planting an enormous number of them actually doesn’t take up that much land area. Obviously, our food pyramid is still missing some important foods, such as leafy greens, but those are small and can be added to our Martian farm without much difficulty.
The final calculation that needs to be performed is to determine how much surface area this will take up in our Martian settlement. The most land-inefficient plant here is our apple trees, which will probably take up an excess of 6 square meters each. This will require 1200 square meters alone. The potato plants will take about 1000 square meters, the rice can be squished together to take up no more than 800 square meters, and our soybeans will total about 700 square meters. In total, our farm needs to have a land area of about 4000 square meters (to accommodate for walking space, watering fixtures, etc.) This equates to a circular dome with a diameter of 72 meters; smaller than the inside of a high school track.
Conclusion
Plants are awesome. With nothing more than a good selection of plants and some human ingenuity, a permanent, self-sustaining colony could be erected on Mars with modern technology. Aided by robot AI, plant seeds could be launched to a pre-built colony to be planted and ready for when humans arrive too. By varying the types of plants cultivated in the settlement, we can control both food production to satisfy the nutritional needs of the colonists, as well as oxygen production for them to breathe. On the other hand, everything that plants need to propagate can be provided by the waste products of humans, the sun, and the Martian atmosphere which already exists. The groundwork has been identified for a true Martian colony, we just need someone to lay the foundation.
As a species, it is important to remember the vitality of setting up a permanent settlement on Mars. We have all of our proverbial eggs in one basket here on Earth. One well placed meteor or dastardly nuclear accident and all that we have worked so hard to create here could be gone in an instant. Having a self-sustaining colony on Mars quenches that dark possibility by separating two completely independent human colonies by millions of kilometers. This project may not be completed for decades, but a permanent base on Mars is the first step towards a safer future for our race. So what are we waiting for? Let’s get planting!
