Mars
Mars, the most similar planet to the Earth. Admired by everyone since the beginning of history, and the house of the gods on Mount Olympus, the highest mountain / volcano in the solar system with an approximate height of 22-23 km which equals 3 times Everest. Mars has seasons, polar caps, volcanoes, canyons and weather so they say it looks so much like Earth, but can our plants survive on the fourth planet of the solar system?
Growing a plant on Mars is not as easy as on Earth.
Mars is a planet with many inconveniences despite our beliefs.
There are many challenges to face such as high radiation, the acidic pH of the soil, low gravity, low temperatures, dust storms, pressure, etc.
Mount Olympus by NASA/JPL
You will think that the UV and more energetic radiations will be lower on the red planet, because the atmosphere will protect it from ionizing radiation, besides Mars is almost 229 million kilometers from the Sun, 79 million farther than Earth, and at that distance from the Sun the radiation must be minimum. But unfortunately this is not so. The Earth prevents the passage of radiation in two ways: the atmosphere and the magnetic field; and it turns out that Mars is short of both. On Mars the atmosphere is 100 times less dense than Earth's and is composed of 96% CO2 and 2.6% N2, so it has no O3 layer and allows the passage of all types of radiation (UV- A, UV-B, UV-C, cosmic radiation, ...), in addition Mars does not have a magnetic field, which is another issue to plant on Mars. High doses of radiation such as those found on Mars are capable of breaking the plant's DNA bonds, in sum it destroys and kills them.
You will wonder why the soil of Mars is a problem, if they say it is super Earthlike. And it is true, Mars has a clayey consistency and is said to be very similar to the basaltic volcanic rocks found in Hawaii. It is also very similar since on both planets the surface is mainly formed by minerals, on both planets they are silicates (silicon compounds with other elements), as for metals, on Earth the most abundant is aluminum (Al) , the second most abundant is iron (Fe), and finally magnesium (Mg); on Mars it turns out that the most abundant are the same metals but in different order, the most abundant is Fe, followed by Mg and the third most abundant is Al; In addition, that characteristic reddish color is given by iron oxide which we can find throughout its surface.
Martian surface by NASA/JPL
We have already seen that Mars is very similar to Earth in terms of composition, but why can't it be planted on Mars? Not everything had to perfect and easy, so Mars challenges us with a few complications. Every substrate has a pH, which indicates whether the soil is acidic or basic. Plants need to grow a more or less neutral pH which is equivalent to a pH of 7. But of course, Mars is not perfect, apart from the fact that its pH is unknown, it is almost certainly believed that it has a very acidic pH, which would kill plants. This problem would be easy to solve including a base in the substrate, so Mars makes things a bit more difficult including high levels of perchlorates, compounds that are considerably toxic to plants that affect both their growth and photosynthetic performance, as in many other factors.
The next problem to deal with would be low gravity. On Mars you would experience 62.5% less gravity than you are used to on Earth. As you know, weight is a measure of the effect of gravity on mass. It varies depending on the mass of the object, the gravity of the planet and the distance between the object and the center of the planet. Given that Mars is 6792 km in diameter, that is half the size of the Earth, it weighs 6.4169×1023 kg which in comparison is one tenth of the Earth, also has a density of 71% Earth’s one, which is equivalent to 3.9 g/cm3, and has 15% of the volume of the Earth, that means 163 billion km3; gravity changes a lot from Earth to Mars. All these factors will cause you go from weighing 75 kg on Earth to 28.2 kg on Mars (calculate your weight on other planets with this link: https://www.exploratorium.edu/ronh/weight/ ). Such a sharp change in weight would hinder us a lot, and the same happens to plants, they will grow in a totally different way than they do on Earth. They will also grow disordered, the roots will be less sensitive to gravity since they will not have such a high force that indicates the center of the planet.
Comparison between Earth and Mars by NASA
One of the most important topics to discuss about Mars is its low temperatures. It seems incredible that the maximum temperature detected on Mars has been about 30ºC, on the other hand, temperatures of 58ºC have been detected on our planet. At the other extreme we find the lowest temperatures recorded, on Mars the record temperature has been -140ºC, so much compared to the -88ºC of the Earth.
As these are extreme cases, these data are not as useful as the average temperature of Mars, which if you do not know it is -63ºC, incredible for the 14ºC to which we have get used on Earth.
You will wonder how it is possible that it is so cold; In large part it is because it does not have an atmosphere capable of creating a greenhouse effect. Although the days last 37 minutes longer than on Earth, and that a Martian year lasts 322 days longer than a Earth year, Mars receives more hours of light, but still does not get warm. Since the Martian year is almost double that of the Terrestrial, the seasons are too, this means more problems, since there will be longer periods of very low temperatures. As expressed in the following graphic.
Graph of temperature variations on Mars - (CAB (CSIC-INTA))
Another great similarity between the planets is the inclination, Mars is inclined 25º on its axis, while the Earth is 23.5º. If we combine this characteristic with the elliptical orbit of Mars, and with the long Martian seasons we get that spring and summer are longer in the northern hemisphere, and autumn and winter are longer in the southern hemisphere.
Last but not least, we can find on the Martian surface the dust devils. Dust devils are Martian sandstorms. These storms can be of small dimensions, that is to say the size of a country / continent, or they can be of enormous dimensions that can cover the entire Martian surface. As there is no air on Mars, dust devils only drag dust and do not carry wind with them, so they cannot cause any material damage or destruction. The problems they can cause can be: covering the solar panels with dust, which would prevent obtaining energy; or in most cases the dust remains in suspension and blocks the light so it does not let the radiation through but does not allow to make anything visible.
Another very complicated issue is the pressure, since the pressure of Mars is 0.6 times that of the Earth. The pressure on Mars varies throughout the year, as on Earth. As shown in the following graphs.
Graph of pressure variations on Earth - (MeteoCiudadReal)
Graph of pressure variations on Mars - (CAB (CSIC-INTA))
The funny thing is that the low pressure causes the plants to behave as if they were drying. Several experiments have shown that if a plant is subjected to low pressures, although the environment is super humid, the plant will work so that it is in a drought, and will end up dying.
Interestingly, studies have found some benefits in a low pressure environment. The mechanism is essentially the same as the one that causes the problems. At low pressure, not only water, but also plant hormones are expelled from the plant more quickly. In this way, a hormone that causes plants to die of old age will leave the body before it takes effect.
Martian greenhouses should be placed in places where the atmospheric pressure is, at most, less than one percent of normal on Earth. These greenhouses will be easier to build and manage if their internal pressure is very low. Once built, the internal pressure of the greenhouses will have to be changed.
The issue of atmospheric pressure and its consequences on plants is a topic that NASA has been investigating for a long time and has made great progress in recent years. In the following link, NASA tells about the greenhouses in which it is working, as well as interesting research.
https://ciencia.nasa.gov/science-at-nasa/2004/25feb_greenhouses
Why Mars and not the Moon?
Since the beginning of time, humanity has been interested in the mystery of the planets. Over the years, thanks to the scientific advances of each era, the dream of exploring space has finally come true.
It has been 50 years since Apollo XI took off from the earth's surface and made possible the arrival of man on the moon. Since then, our knowledge about space has been increasing thanks to the exhaustive work of the scientific community that is always looking for new objectives. The idea of exploring new frontiers is irresistible, so the curiosity of human beings in space is now focused on Mars.
Buzz Aldrin in the Moon, NASA
Unmanned space travel has finally taken us to the Martian surface. Through new knowledge, scientists cooperation and the financing of several countries, this generation has contemplated a dream come true: the physical exploration of the red planet.
Curiosity rover on Mars, NASA/JPL-Caltech/MSSS
We know that Mars brings us a great source of information that helps us understand part of our Solar System. Exploring the rocky surface of Mars is giving us a lot of data about how our planet could have been millions of years ago and maybe how may the Earth be in the future.
The possibility that Mars can one day be inhabited, is part of what motivates us to work on this project as well as to be able to contribute in some way in future researches.
Focusing nowadays on Mars' exploration is a great challenge in the same way that 50 years ago the Moon was the first objective of space exploration, now setting foot on Mars will become the next goal of future generations.
Soil and microbiota
Essential nutrients:
Essential nutrients:
For plant growth, nutrients are needed. Among these, the main ones are N, P and K. Usually, plants are not able to assimilate them, so these nutrients need to be previously transformed by a series of microorganisms. Therefore, it is quite likely that you need to bring a microbiota to Mars if you want to plant on this planet.
Cycle of the nitrogen:
For plants to live, not only on Mars, but in any area it is necessary to have the Nitrogen cycle. If you do not know what the nitrogen cycle is, it is a cycle that is based on supplying N2 to living beings and on which the balance of composition of the biosphere depends. It can be summarized as follows.
- Atmospheric N2 fixation: certain bacteria can capture atmospheric N2 and transform it into ammonia.
- Transition from ammonia to ammonium
- Nitritación: Transition from ammonium to nitrites.
- Nitration: Transition from nitrites to nitrates.
- Denitrification: Transition of nitrates to atmospheric nitrogen.
Therefore, according to this, we will need the following microorganisms:
- Nitrogen fixatives (probably anaerobes: azotobacter, clostridium, klebsellia...)
- Nitrosomonas (nitritación)
- Nitrobacter (nitration)
- Denitrifiers (anaerobes: Bacillus ...)
Martian soil:
As we have already explained, perchlorates are considerably toxic compounds for plants that affect both their growth and photosynthetic performance, as in many other factors. Therefore, it would also be necessary to carry an organism that was able to metabolize perchlorates. Some examples would be:
- Firmicutes
- Moorella perchloratireducens
- Sporomusa
- Archaeoglobus fulgidus.
Fertilizers:
The first fertilizer we could use is urea present in human urine. Urea, once found in the soil, would be converted to ammonia, ammonium ... By the oxidizing bacteria of ammonia or ammonium (since they contain the enzyme urease). Once transformed, it would be incorporated into the nitrogen cycle itself. However, this type of fertilization can also be harmful on certain occasions:
- Nitrification would cause an increase in the acidity of the soil, since the number of hydrogen ions in it would increase. To neutralize it, it would be convenient to treat the soil with a base (for example calcium carbonate) or use microorganisms that increase the pH.
- An excess of urea, and therefore nitrogen, can affect the germination of the seeds or can even burn the plant. Therefore, the appropriate amount should be used according to what we are going to plant.
The second fertilizer we could use would be human feces. In this case, it would be necessary to compose them, since they contain a large number of microorganisms that we are not interested in being in the soil, as they could be harmful. In Haiti, an association called SOIL developed a relatively simple and cost-effective composting system. It is simply about adding carbon to the matter (extracted from sugarcane) in order to activate microorganisms. These would use the raw material and, as a result, release N, P and Mg. In addition, these bacteria would generate the heat necessary to eliminate any pathogen that was present. The only thing is that the process takes a few months to complete, although it is also true that SOIL carries it out with very large amounts of waste, so if this amount were smaller, the process would surely accelerate.
Microclimate:
As we have explained before, the problems of the climate and the air are the low temperatures and the atmosphere which is very scarce in O2. Both factors pose a problem for the development of life.
Given the low temperatures, it would be best to create a structure (greenhouse) as isolated as possible, to avoid the entry of cold from the outside and thus maintain an optimal Tº for the development of plants.
On the other hand, lack of oxygen is more complicated to solve. We have several options:
- Obtain O2 from organisms that are able to metabolize perchlorates and release O2 accordingly. However, it is not known if the amount of O2 released would be sufficient.
- Obtain O2 from water hydrolysis, water obtained from Mars. However, first you would have to find out how to get that water and how to purify it.
- The Sabatier reaction: CO2 + 4H2 → CH4 + 2H2O. In this way, CH4 could be used as fuel, oxygen would be released from the water using electrolysis, and the resulting hydrogen would be recycled back into the Sabatier reaction. It is also an exothermic reaction (releases energy). It would only be necessary to bring H2 from Earth (it is light) and CO2 would be obtained from the atmosphere. A reactor would be needed for this (300-400 ° C and Ni as catalyst).
- Another possible reaction would be the reverse gas water change reaction, CO2 + H2 → CO + H2O. It happens in the presence of an iron-chromium catalyst at 400 ° C. O2 is obtained from water by electrolysis and only a small amount of hydrogen brought from Earth is needed. Oxygen could be used as a rocket fuel oxidizer.Atmospheric CO2 electrolysis 2CO2 (+ energy) → 2CO + O2
Water:
Water is an essential factor for the development of any living being. Currently, it is known that there is water on Mars, mostly in a solid state (in the form of ice). This is due to temperatures and low atmospheric pressure (610 Pascal), which cause water to pass directly from the solid to gaseous state, or vice versa, without passing through the liquid.
For our goal, we need liquid water. If we wanted to extract water from Mars, we would first have to defrost it and then filter it (since it contains a large amount of salts). In order to do so, we may need to counteract atmospheric pressure in some way (and the Tº), since they are responsible for sublimation / freezing of water.
The images, taken from NASA’s web, shows us (green, blue dots ... etc) the regions of Mars in which there are glaciers. In addition, last year it was discovered (with the Mars Express probe), the existence of a liquid water about 20 km long and about 1.5 km below the ice of the South Pole. It was not known whether it was a lake or porous rocks infiltrated with water. However, it is a factor to take into account, since if we could draw the water directly liquid, it would not be necessary to defrost it but simply filter it through a reverse osmosis process.
On the other hand, it is likely that defrosting would have to be carried out in a place isolated from Martian conditions, since the T°, pressure ... etc. They make it impossible to have liquid water on the surface. To defrost it, you could apply heat (using solar energy), or use waves (from a microwave for example) to increase its Tª and get it to defrost. Once we got the liquid water, we just had to filter it.
In addition, we would have to take into account the presence of water to choose the region in which we would build the greenhouse. As for atmospheric pressure, we are likely to have to install a pressure system inside the greenhouse itself (it is 0.6 times that of the Earth).
Greenhouse
Transforming a plant to resist such temperatures, pressures, dust storms, etc., is practically impossible, so we have created our own Martian greenhouse.
The main functions of the greenhouse will be to protect plants from much radiation, extreme temperatures and dust devils. But before starting to describe the greenhouse, we must comment that we are not going to another planet to infect or contaminate it. Therefore, we will insulate the greenhouse from the surface, that is, make a greenhouse completely closed both by the roof and by the part of the ground; We will divide the greenhouse floor and the Martian soil by a metal plate so that the soil of Mars is not contaminated. Once the biosecurity issue is over, it's time to start describing the greenhouse.
We have considered several greenhouse format options, but we have opted for a tunnel type greenhouse. In order not to waste a lot of volume, and for reasons of energy savings, the greenhouse will be organized in a system of tables, this means that the plants will be grown on a table and not at ground level. These tables will have two functions depending on the height. The lower part of the table, which will be the freshest, will be used as a warehouse in which we will store the potatoes that we grow. Then the high part of the table will be used as a "pot" that is, the growing area.
The basic of the greenhouse is its structure. The greenhouse chassis will consist of an aluminum structure. We have chosen aluminum for its lightness, strength and difficult oxidation, as it will be exposed to perchlorates that are highly oxidizing compounds.
The following graph shows the radiation shielding capacity according to different density materials (NASA).
When radiation hits a material, the radiation particles divide and multiply. They multiply more or less depending on the material with which they impact. In the graph we can see that aluminum is the one that offers the most protection, which means that it divides the particles of the radiation into smaller amounts. That is another reason why we have selected aluminum for our chassis.
On the other hand, the material that will be in contact with the outside will be glass, since it is capable of letting light through and does not wear out as much as methacrylate, in addition to being resistant enough to withstand dust devils. The function of the glass will be to cover, maintain and hold the insulation and the other layers of the greenhouse cover.
The temperature would be a problem if we did not find a good insulator or a good heating. In this case we have decided to include in our greenhouse a super insulator created by NASA and Harvard University. The super insulator, called Aerogel, has incredible properties such as that it is composed of 99% air, it is also flame retardant, is super resistant and is capable of blocking extreme temperatures of both cold and heat. Once the greenhouse was closed and the Aerogel layer was installed on the roof, the greenhouse effect would begin to be produced inside it, so that with this material we already get rid of the inconvenience of low temperatures.
The issue of radiation is already a bigger problem. Radiation does not affect all regions of Mars in the same way and less with the same intensity, as seen in the following image.
Blog by Daniel Marin-Naukas, who in turn has been taken from NASA
The image shows the dose of radiation on the Martian surface due to cosmic rays. The highest regions are the least protected, being located outside the atmosphere. Knowing that radiation can be deadly, we are not going to risk, that is, knowing that less radiation hits the North Pole and that there is also water in form of ice, the option of implanting the greenhouse at the North Pole is the most viable. Another option would be to implant it in the Gale crater, the most studied crater on Mars and where it is shown that less radiation arrives. As shown in the following graph.
Graphic measurement by RAD, included in the NASA Curiosity rover
Where it indicates "Landing" means that the Curiosity rover landed in the Gale crater, and as observed, the radiation fell considerably. So the option of implanting the greenhouse in the Gale crater is not ruled out.
We were talking with Juan Ángel Vaquerizo (physicist of the CAB-INTA) and with Iñaki Ordóñez (doctor of astrophysics from the University of the Basque Country) and they both told us that they were working on creating a material that would let the light pass and in turn stop the radiation. Investigating the Aerogel we saw that it stopped a small part of the radiation, but did not stop long enough for the plants to live. Therefore we had to investigate different materials to prevent radiation. We considered inserting a small atmosphere in the greenhouse, as another part of the roof, but all that changed when we discovered that there were some lenses that could help us. The UV400 lenses are glasses used for extreme light conditions. These lenses protect from all radiation with a wavelength less than 400 nm which means that it protects from all UVs since neither A nor B nor C exceed 400 nm. Therefore, another of the layers of the cover will be UV400 lenses for UV protection.
The big problem came when Juan Ángel Vaquerizo told us and warned us of cosmic radiation. Cosmic radiation are subatomic particles from outer space with a very high energy thanks to its high speed, close to that of light.
The first thing that came to mind were astronaut helmets, what did the lenses of those helmets wear so that the radiation does not harm the astronauts? We did not find anything in relation to the components of the hull, however we read that astronauts do not suffer any damage since they make short-term space trips, which made it a bit difficult for us to research since our plants must remain fixed on Mars.
Astronaut helmet, somehow protecting from radiation-NASA
We also inform ourselves that the materials that best stop the radiation formed by protons are those with elements of low atomic number, such as hydrogen. The use of several layers of polyethylene (hydrogen-rich hydrocarbon) and water is believed to be the best way to protect the crew of a ship. The problem with this idea is that it is based for a ship, so the materials are opaque. If we include these materials in the greenhouse we will protect the plants from radiation, but we will deprive them of the light and it would be a great energy cost to supply them with artificial light.
Another option would be to include active shielding through magnetic or electrostatic fields, that is, create our own magnetic field around the greenhouse. However, this system consumes a lot of energy, making it necessary to use nuclear reactors or gigantic solar panels. This idea was already developed by NASA in this document. NASA's electrostatic field document
Finally, as a more fictitious idea is the possibility of including a plasma layer on the roof of the greenhouse, and in this way it is believed that the cosmic radiation would stop, which would make planting on Mars possible.
As you can see, the issue of radiation is the most complex thing in otherworldly life, and it is not yet known how to deal with the problem.
Believed future colonies in Mars
We start with the inside of the greenhouse, once the operation of the tables and the structure is explained, we have to explain how we would do to water the plants. For reasons of saving water, the irrigation system will be drip. In addition, if you need to add any volatile compound, nutrient, medication, fertilizer, ... this will be the easiest way to deliver them.
In the months of less light and in case that a dust devil block’s the light, it will be necessary to supply light to the plants, so we will need a source of energy, and as Mars rovers do, they will be solar panels. The lighting system will consist of LED type lights. The LEDs are lamps that also, in addition to having a better spectral output and longer duration, generate a lower energy expenditure, although they have a higher light intensity, since they can be placed near the plants, without burning them. The lights will be blue and red colors as it is studied that encourage the growth of plants better than traditional lights.
All this would be of no use if we did not include certain regulators. There are a number of regulators that will have to be mandatory such as pressure, temperature, humidity...
As we have explained before, plants under very low pressures dry out, so the pressure of the greenhouse should be increased in some way, which would be by inserting gases such as O2 or N2 in an appropriate %, that is, essential gases for the cycle of a plant. That pressure had to be controlled since if we passed, the greenhouse materials could suffer cracks and with the change of Mars-Greenhouse pressure, it could explode.
The greenhouse will produce a greenhouse effect, but you always run the risk of overheating, or of cooling because a dust devil is blocking sunlight. Therefore, a heating and cooling system must be implemented.
CO2 in small quantities is very beneficial for plants, but on Mars 96% is CO2 and that would negatively affect the growth of plants, so a gas valve system should be implemented. This system depending on the level of CO2, expelled or not a certain amount of gases to create a viable atmosphere for plant survival. These gases could be O2, N2 or any other beneficial for the respiration and photosynthesis of plants, and that do not pose any risk to them.
A humidity regulation system should be included, since if the plants are in high or low humidity, they can be dried or drowned. In low humidity situations the solution could implement a series of humidifiers, and in cases of high humidity, we could implement, in the form of capsules or in some other way, polyamide, a material used in baby diapers that absorbs all types of liquids, humidities...
The temperature of the pot should also be controlled, since if it is very cold the roots could freeze or worsen productivity.
As you have seen, Mars is a planet that, however similar it may be to Earth, has many other factors that make it virtually uninhabitable. We do not pretend to launch a completely reliable and ready greenhouse to withstand all the challenges of Mars; With this research and the construction of this greenhouse we pretend to learn about Mars and its adversities in addition to learning different techniques of protection from radiation, temperature, pH.... With this document we also try to make people aware of the difficulty of investigating other planets and climates, which NASA, ESA, CSIC or any other research group faces.