Colonizing Mars comes with a lot of challenges and quandaries. The first questions that come to mind are probably something akin to: 'how do we get people there?' and 'what do we take with us, and what can be manufactured on location?' However, since the distance to the red planet is so enormous, questions regarding sustainability and self-reliance are perhaps just as essential.
For a long-term colony to really become viable, we will need to be able to 'live off the land,' so to say. In addition to things like secure food production, we will need a reliable source of oxygen. One possible solution is to produce oxygen from Martian brine, a high-concentration solution of salt (NaCl) in water (H2O). The potential benefits are great as it is predicted to consume 25 times less electrical power to produce compared to conventional oxygen production.
In this article, David Rothery, Professor of Planetary Geosciences, explains a Washington University research paper, recently published in PNAS
By David Rothery
The famous Jezero Crater on the red planet as it might have looked billions of years ago. There may still be brine underneath the Martian surface that can be used to generate oxygen and fuel - Image Credit: NASA/JPL-Caltech via Wikimedia Commons
Unlike the initial short-stay visits, long-term bases on Mars will have to be self sufficient in as many essentials as possible.
A lot of research has gone into preparing for In Situ Resource Utilization (ISRU) that could help to build and sustain a lunar base. Now, similar ideas for Mars are catching up, with a new study, published in PNAS, suggesting a way to use the brine (salty water) found on Mars to make breathable air and fuel.
“Living off the land” will be even more important on Mars than on the Moon, because Mars is much further away – making transport costs (and time) correspondingly greater.
One major resource issue is how to provide enough oxygen for the Mars-base crew to breathe. Mars has only a thin atmosphere, with a surface pressure less than a hundredth of the Earth’s. Even worse, it is 96% carbon dioxide with only about 0.1% oxygen. Earth’s atmosphere is 21% oxygen.
NASA’s Mars2020 rover, Perseverance, which is already on its way to Mars, carries an experiment called MOXIE, a name imaginatively contrived from Mars OXygen In situ Experiment.
The Perseverance Mars Rover with its main experiments labelled. - Image Credit: NASA
MOXIE’s purpose is to demonstrate that oxygen can be made from the carbon dioxide in Mars’s atmosphere by using electricity to split it into a mixture of oxygen and carbon monoxide, via a process called electrolysis. If this works as expected, the oxygen could be collected and used to give colonists something to breathe or as a component in fuel. The carbon monoxide would be unwanted, and would be vented back into the martian atmosphere.
Oxygen from martian brine
A new way has emerged, however, that would consume 25 times less electrical power to produce the same amount of oxygen. No matter whether you use solar cells or a radioactive source to generate your electricity, the available power is limited, so this is an important gain.
In the new study, a team from Washington University in the US, demonstrate how electrolysis can be used efficiently to produce oxygen and hydrogen simultaneously from brine. It turns out that when you start from a concentrated solution of magnesium perchlorate, it is relatively easy to split the water component of the brine into oxygen and hydrogen using electrolysis.
This may sound exotic, but magnesium perchlorate is what the briny water at and near the surface of Mars appears to consist of, as seen for example when liquid droplets appeared on the legs of NASA’s Phoenix lander, which touched down in Mars’s far north in 2008. The Curiosity rover has also found evidence of calcium perchlorate brine just south of the martian equator.
Droplets, believed to be a solution of magnesium perchlorate, on a strut of the Phoenix [lander leg eight (left), 31 (center), and 44 (right) days after landing. - Image Credit: NASA/Jet Propulsion Laboratory-California Institute of Technology/University of Arizona/Max Planck Institute.
Perchlorate salts are good at scavenging water from the driest of atmospheres, hence the droplets on the Phoenix lander’s legs. They can depress the freezing point of a liquid to as low as −70 °C, which prevents concentrated perchlorate brines from freezing even at Mars’s low surface temperatures. There are places where the appearance of dark, moist streaks is thought to be the seasonal flow of brine to the surface.
Dark streaks on the wall of Juventae Chasma, Mars, which are possibly seasonal seeps of brine. - Image Credit: NASA/JPL/University of Arizona
If you land where there is brine available, the new study argues, you could make as much oxygen as you like – provided you have unlimited brine and power. The breakthrough in the efficiency of this perchlorate brine electrolysis has to do with the make-up of the oxygen-producing electrode. For this, the study used a variety of a mineral called pyrochlore, consisting in this instance of an oxide of lead and ruthenium. Pyrochlores have a wide range of technological applications, including, as in this case, as an “electrocatalyst” to make electrolysis faster and easier.
Read more: Water, water, everywhere – where to drink in the solar system
Practical options
It remains to be seen whether MOXIE-style electrolysis of martian carbon dioxide or pyrochlore-enabled electrolysis of martian brines proves the more practical way to make oxygen on Mars. The hydrogen from brine electrolysis is a bonus that you don’t get by electrolysis of carbon dioxide, and this could be used as rocket fuel as the study points out. Actually, if you want to do that, you’d need to use up the oxygen as the complementary component of the fuel. But at least that gives you a choice: breathe the oxygen or use it in a hydrogen-plus-oxygen fuel mixture.
Neither option would be available during the several month-long journeys to and from Mars, for which recycling solutions would have to be found, as today on the International Space Station. These would also be important on the surface of Mars.
Recycling of consumables on the International Space Station. - Image Credit: NASA/AntiNeo via Wikimedia Commons (click on image to enlarge)
There is another way to replenish oxygen of course, which would be to grow plants in the Mars base. These could absorb the carbon dioxide exhaled by the crew and liberate oxygen by photosynthesis. Crew members could also eat some of the plants, which would be a welcome source of fresh food.
Sources and further reading:
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