In principle you could grow plants on Mars the way Matt Damon did in the Martian, using faeces and Martian soil and mixing them to grow food. In principle it works but he was also very lucky.
We know that Martian soil, or regolith, as we call it, is sterile so you would have to add some fertiliser, the excrements for example, to be able to use it.
However, we also know that Martian soil contains many toxic elements such as heavy metals and perchlorate, which is an chlorine oxide that can be found in some bleaching agent. These toxic compounds may not be a problem for the plants but they could be a problem for the people eating these plants.
In the film, we don’t know whether Matt Damon treated the Martian soil anyhow to remove these toxic compounds. He could have done that either by first using non-edible plants that would suck out the heavy metals and perchlorates, or he could wash the soil with water or use bacteria to remove the toxic elements.
- How Matt Damon did it
If he hadn’t done that, he could actually get sick or even die because of the accumulation of heavy metals in his body.
Another issue is the usability of human excrements for the purpose of growing food. On Earth, in agriculture, we usually don’t use human waste as a fertiliser to avoid spreading pathogens.
If we want to use human waste, then it has to be really degraded and the toxins have to be removed.
In the film, Matt Damon uses his own poop, which is actually OK because that only contains his own pathogens, which would not hurt him.
However, he also uses the poop of his crewmates and that could be another story. In the film, luckily, this poop is freeze-dried and stored outside and we can expect that all the pathogens would have been destroyed. Had he used fresh poop of his crewmates, he could have gotten sick.
- Lucie Poulet explains that Marsonauts would have to be vegetarians
What Matt Damon does reflects the existing concepts that have been developed for a future mission to Mars. If we go to Mars, we would have to recycle human waste to grow plants. We wouldn’t be able to bring all the food and soil from Earth. We could use Martian soil. There is actually a team in the Netherlands that is trying to grow plants in simulated Martian soil. This stimulant is made by NASA using volcanic soil from Hawaii and they have been quite successful.
Three years ago, I took part in a four-month Mars mission simulation in Hawaii and I was actually growing plants using soil from the volcano. Some pots only had volcanic soil and others had volcanic plus regular soil and both worked.
If you have a soil like volcanic, which is sterile and you add fertiliser, it is going to act like a hydroponic system.
My bet is that the first crews on Mars would actually be relying primarily on hydroponic systems to grow plants rather than using Martian soil. We can use only very little water for those hydroponic systems using the nutrient film technique, which is important as water is also hard to come by on Mars. Using water and some fertiliser would be safer than using the toxic Martian soil. And you can indeed use degraded human excrements as the fertiliser.
The idea of recycling everything, including human waste, urine and exhaled air to grow food, make breathable air and drinkable water is called a closed loop system and it is exactly what we need if we want to explore distant planets.
On the International Space Station the astronauts have a physical-chemical system that recycles urine into drinkable water so the astronauts are essentially drinking their own recycled urine.
As part of my PhD, I am working on a project of the European Space Agency called MELISSA, which stands for the Micro-Ecological Life Support System Alternative.
- Running a greenhouse to Mars will be tricky, explains Lucie Poulet in To Mars, a documentary shot during a simulated mission at the Mars Desert Research Station in Utah, the USA
MELiSSA is essentially a closed-loop system designed to one day act as a life-support system for humans. It is based on microorganisms, algae and bacteria, and plants. It uses only biological processes to recycle human waste to create air, water and food.
Human waste is degraded by bacteria, which are removing toxins and transforming the waste until we have simple elements that we send to the plants and to the algae. The plants and the algae use these elements together with the carbon dioxide exhaled by the crew to produce oxygen, food and drinkable water.
It is essentially mimicking a lake ecosystem, where the astronauts would be the fish and the plants that are growing in the lake are basically the same and everything that would be happening in the mud on the lake floor is equivalent to the bacteria we are using in MELiSSA.
We are mimicking a natural ecosystem in a closed environment with different compartments. The biggest difficulty is to make sure that your bacteria do what you want them to do and that you don’t have contamination between the compartments. That would ruin everything.
- European astronaut Samantha Cristoforetti introduces the Melissa life support experiment
So far, it’s at the prototype stage but it’s working really well. Currently, the system can close the air loop with a crew of three rats. The rats are the astronauts and they are breathing air produced by the algae. The rats are exhaling CO2, which is in turned absorbed by the algae.
The system has not been tested in space yet. It will take maybe 30 to 40 years for it to reach the stage where it would be able to sustain humans. However, before that, we may perfect various parts of the loop – like have a small greenhouse in space, providing some food and partially recycling oxygen and water.
When humans go to Mars or anywhere else in the Solar System, we wouldn’t rely on a single technology to provide all the food, oxygen and water, they need. We would have a combination of systems using biological processes and physico-chemical processes. We would have two systems for recycling water – one would be based on plants and the other would be physic-chemical, similar to that currently on the International Space Station and the same would go for air. For food production we would obviously only have plants at first.