How could humans live on Mars?

Beyond Earth’s atmosphere, astronauts on the International Space Station (ISS) are exposed to 250 times the radiation experienced on the surface of our home planet. This increases to 700 times the radiation for missions beyond Earth’s orbit, which are without the protection of Earth’s magnetic field. Astronauts spend months at a time on the ISS, while missions to the Moon subject crews to the higher levels of radiation but for a shorter period of days or weeks. By this measure, Mars missions would be by far the most damaging in that they combine long mission length and high radiation exposure.

In order to gain an understanding of the effects of the space environment on the human body, NASA and the ESA have been conducting long-term studies including one that followed twins Scott and Mark Kelly – Scott conducting lengthy missions on the ISS, while Mark remained on Earth. This gave researchers a rare opportunity to compare two individuals with the same genetic makeup in two very different environments.

The results showed that Scott’s immune system reacted in the same way to vaccines in space as Mark’s did on Earth. This means that vaccines that may need to be administered during a long mission in space should be just as effective. Researchers did see differences in Scott’s gene expression and changes in telomeres compared to his twin on Earth. Gene expression is DNA’s way of giving instructions to the body. Telomeres are the ends of DNA strands, and they protect chromosomes from damage. By studying how gene expression changed for Scott as part of the Twins Study, healthcare professionals could learn what aspects of treatments need to be modified or changed in order to tailor them to the immune system in space.

Scott’s telomeres lengthened in space over time compared to Mark’s. While long telomeres were once thought to assist with a longer life span, it is now understood that at both extremes – short and long – they are detrimental to our health. Generally, short telomeres can negatively affect organs, while long telomeres increase the risk of cancer and other disorders. The Twins Study has provided NASA with an excellent baseline for targeted treatments and health plans for extended missions in space.

On Mars, just as on Earth, our basic requirements are breathable air, food, water, fuel and shelter.

Without a regular shipment of oxygen and water supplies from Earth, settlers on Mars will need to look to the local environment to extract what is needed. This is often referred to as ‘in-situ resource utilisation’. 

One of the proposed technologies is to extract oxygen from the thin carbon dioxide atmosphere (the chemical name is CO2, for the one carbon atom and two oxygen atoms contained within each molecule of the gas).

NASA’s Perseverance rover contains a small-scale demonstration of this technology, with its Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE for short. Although the device is not much larger than a lunchbox, it is able to convert carbon dioxide into oxygen at the same rate as one small tree on Earth. That equates to enough oxygen produced over two years for a human to survive just 3.5 hours. While this is hardly enough to provide for a small settlement, it is only operating on about 100 watts of power – available through Perseverance’s main power system. With a much greater power source capable of generating tens of thousands of watts, a small habitat could be supported.

Water can be found on Mars but in the form of ice, and in most exposed surface areas it is not present. It has been detected at the polar icecaps but, even then, it is locked away under thick slabs of frozen carbon dioxide. Water ice could be preserved and accessed in deep craters, in caves and in partially collapsed lava tubes where sunlight does not reach. NASA’s Phoenix lander literally dug up evidence of water ice just beneath the surface of the planet, but this was in a polar region that is not favoured for human settlement.  

Compounding matters is the fact that water detected thus far on Mars has a high concentration of perchlorate salts that are toxic to humans – a filtration process or, potentially, use of a hardy strain of bacteria would be required to detoxify the supply. 

Many chemical processes that produce viable fuel for rockets also produce water, so humans may not have to risk life and limb or precious tools to extract liquid water directly from water ice on Mars. Water is known chemically as H2O – two hydrogen atoms with one oxygen atom. Therefore, it is often described as a useful combination of rocket fuel (hydrogen) and oxygen. 

Using electrolysis, the process by which electricity is used to separate the hydrogen and oxygen atoms, it is possible for water to provide both fuel and breathable air, although the aforementioned perchlorates, the extremely low temperatures Mars reaches and its lower gravity significantly reduce the efficiency of the process.

In terms of food requirements, experiments are under way on board the ISS and on Earth to grow crops under LED lights, both with hydroponic techniques and in simulated Mars soil. Hydroponics involves keeping plants rooted in nutrient-enriched water and, thanks to data gathered by generations of landers and rovers, scientists on Earth can create soil mixes that approximate to Mars chemically and structurally.  

‘Soil’ is a slightly misleading term for the substance on Mars, which is better defined as ‘regolith’ – inorganic dust and broken-up rock. Some areas of the surface and subsurface contain clays and basalt (cooled lava), and there is a strong mineral presence including iron oxides – commonly known as rust – which give Mars its iconic hue. While this is hardly what can be described as ‘rich soil’, it is the basic foundation for a medium in which plant life could be grown.

The ability to produce water would bring us a step closer to food production, but we need some organic material in the mix too. Studies of cyanobacteria, also called bluegreen algae, have shown that it can grow with limited resources. On Earth, it is often seen as a natural menace due to its fast-spreading nature. On the ISS, as part of BIOMEX (BIOlogy and Mars EXperiment), organic samples were placed outside the space station, exposing them to the extreme environment of space. 

Simulating the Martian environment, samples that had cyanobacteria mixed in a Mars soil simulant under a filter that blocked some harmful radiation, survived. Samples that were not mixed with the soil and were also exposed to a full spectrum of radiation died, the samples that were set up in a replicated Mars environment survived for over 700 days in space. Although their DNA was damaged, they were found to repair themselves after rehydration on Earth. Based on these results and other lab simulations, a strong or modified strain of this algae could be used to enrich the Martian soil in order to grow edible vegetables on the Red Planet.

Other experiments have highlighted the benefit of hydroponics to enable vertical farming. By housing racks of edible greenery in the spacecraft that would take humans to Mars, the contents for a Mars greenhouse would be ready to move onto the surface upon arrival.

Water, however, is a precious commodity and heavy in great quantities. Aeroponics takes the process of soilless gardening a step further by suspending plants and their roots in mid-air and regularly exposing them to a nutrient mist. This makes efficient use of water en route to Mars, as well as significantly reducing the initial launch payload from Earth. In many ways this form of food cultivation sidesteps significant issues such as the spread of plant diseases and the acidity of soil. 

One disadvantage is that the misting needs to be carefully monitored and the content of the mist needs to be precisely formulated. Failure in either regard could lead to a disastrous loss of crops. At the very least, this form of farming could kick-start the food supply on Mars on arrival until enough algae and compostable waste is accumulated to switch to more traditional soil-based farming methods.