In the previous post of this series, we answered the question of whether we can grow potatoes out of potatoes; while the answer to that question is yes, we still need to look at various other aspects in order to determine if we can grow potatoes on Mars the way Mark Watney did in the movie.
The next step of determining the accuracy of growing potatoes on Mars is to determine if the soil on Mars can facilitate the growth of Potatoes. As mentioned in the previous post “Potatoes grow best in soil that is rich in organic matter and well-drained, they also require plenty of sun. They grow better in loose soil. However, they cannot grow well in extreme heat or dry soil. A soil temperature of around 40 Fahrenheit or 4.4 Celsius and the soil slightly acidic (a PH of 5 to 7 is ideal). However, technically potatoes can grow in any type of soil except alkaline and saline soils.”
The composition of soil on Mars is almost entirely made up of mineral matter, with small amounts of water but present mainly in the form of solid ice and very little in its liquid state. Moreover, since living things don’t exist on Mars, the Martian soil is deprived of bacteria and micro-organisms and hence has no organic matter present. The atmosphere on Mars is extremely thin and hence there is very little atmospheric gas present in the soil. The mineral matter of the Marian soil is clay and slit sized particles that come from weathered volcanic rock, but overall Mars has sandy soil. It is also relatively homogenous since the dust storms move the particles around.
Now that we know the type of soil present on Mars - can we grow potatoes on Martain soil? The answer is probably yes, and the steps that Watney takes are quite accurate. All essential nutrients are already present in the Martian soil; unfortunately, the levels of nutrients present are too low to actually grow the potatoes; similarly, there is no organic matter present. We will require fertilizers to enable the growth of the potatoes and combat these problems. This is exactly what Watney does when he collects the excreta of his fellow astronauts.
Human faces have a bacterial biomass composition of 25-54% in dry solid form. Also, it has a PH of 6.64 and is composed of 74.6% water. This takes care of the absence of organic matter and adds extra moisture to the soil. Many countries actually use human feces as fertilizers for cultivating their farms (yes, we are again looking at you China)
A second problem associated with growing potatoes on the Marian soil is the lack of water. Mars has polar ice caps and some liquid water in its soil but that is insufficient and too salty. Hence the water will have to probably be sourced from the earth or purified. Another aspect which the movie got right. In the movie, we can see Watney attempting to purify water by creating a moderate flame in space similar to a bunsen burner and using that to purify the water. We can also see him wetting the soil before he plants the potatoes.
However, the Martin soil has high levels of chlorine in the form of molecules of perchlorates; this is harmful to both plants and people alike. In consequence, Watney would have to have used something more than just fertilizer. Again, as aforementioned in the previous post a 15-year gap, well now 14, can make a huge difference. By then scientists may have come up with an efficient compound or mixture which can neutralize the perchlorate molecules, which Watney would have mixed in the fertilizer. In the next post, we will analyze how accurate is Watney’s method of purification of water and is it possible to implement it. This is the second post in the ‘Martian Potato Series’
Fun Fact: “Soil, by definition, includes organic matter. Since there is no organic matter on Mars, there is technically no soil. The proper term for the surface material of Mars is regolith, which is a broad term for the loose material that covers the surface of some planets (Earth, Mars, Mercury) and Earth’s moon. Soil is a type of regolith. Scientists commonly refer to Martian “soil” despite this technical difference.” - letstalkscience