Using the Martian atmosphere as a resource

Martian Resources

The Mars atmosphere cannot support life. But can it be used to sustain life? Maybe. Let's look at the basic components of the Martian atmosphere. Over 95% of it is carbon dioxide. Although it isn't fit to breathe, it can support plant life. A little over 3% of the Martian atmosphere is nitrogen. This can be used for fertilizer. While it isn't poison, it isn't oxygen. Close to 2% is argon, which is a noble gas. Argon has its uses, but it isn't going to help sustain life processes. This almost covers it all, but there are a few trace gases of interest. Water vapor is available too.

On Mars, oxygen is a trace gas, as is carbon monoxide. Although they are trace gases, there may be a way to harvest these gases. Carbon monoxide is combustible, and oxygen supports combustion. There's about three times as much oxygen as there is carbon monoxide. Therefore, you can burn off the carbon monoxide for energy with some oxygen left over. There may be enough to make it worthwhile to collect it so as to run the distillation process.

As space enthusiasts know, it gets cold on Mars. Also, the Mars atmosphere is pretty thin. Therefore, if you are going to use it for in situ resourcing, you will need to gather a lot of it, and compress it. Or should you? What if you were to lower the temperature to freeze out the carbon dioxide? If you do that, you remove 95% of the gas you started with. The gases remaining will be more concentrated.

The concentrations will be about 8% oxygen. Very interesting! Not much higher than that would make it capable for us to breathe. How about that?! As for nitrogen, the new concentration would be about 55%. The Earth's atmosphere is 80%. That's also very interesting. But carbon monoxide would be 3%, and that's bad. Argon would make up 34% or so or the remaining, and argon isn't that interesting in this context. The rest would be trace gases of this processed batch of gases.

Now it may make sense to compress it, as these gases are only small parts of the Martian atmosphere, and we need to process a whole lot of it in order to collect useful amounts. When you compress a gas, you will heat it up. By the time you've heated it up, you will need to cool it down again to reach cryogenic temperatures for air distillation. At these temperatures, the gases will condense into liquids. They'll do so at specific temperatures, which gives the opportunity to separate them out one at a time. We use a table to see this better.

• co2   194.68°K    dry ice (carbon dioxide)
• o       90.188°K    to liquid o2 (oxygen) 
• ar       87.302°K   to liquid ar (argon )
• co      81.6°K       to liquid co (carbon monoxide) 
•  n       77.355 °K      to liquid n (nitrogen)
• sym     °K             results  (name)     NOTE:   0° C =  273.1°K

Science question:  What temperature K will yield water ice?

The trick is to lower the temperature of the entire batch and the gases will separate out, starting with oxygen. A little lower will yield argon. Lower still yield carbon monoxide. Since the remainder is nitrogen, just collect the gas, and your left with liquid carbon monoxide. Some impurities may remain in each fraction, but the results should give fairly clean parts of each with a final temperature of just under 81.6 kelvin.  (kelvin is centigrade, but starts at absolute zero)

The hope is to be able to run the entire system on a self sustaining basis by burning the carbon monoxide with oxygen. That will supply heat needed to run the apparatus that yields these products. That may be asking a lot, since a lot of gas has to be processed, and the Martian atmosphere is very thin. To judge that is beyond my pay grade, so I'll stop without an analysis of the economics.

Since Mars is already cold, it should be relatively easy to get temperatures down to the point of a freezing of the carbon dioxide. It's already cold enough in the polar regions to do that naturally. At night, temperatures may fall pretty close to that in even in equatorial areas.

It doesn't stay cold all the time, but if provisions are made, it may be possible to keep it cold all the time. Thin air is a poor conductor of heat, so insulating a cold trap shouldn't be as difficult as on Earth. Starting cold and keeping cold could be further achieved by using the dry ice to cool down the incoming air to be processed. Therefore, the initial separation could be made fairly cheap on the energy expenditure.

Processing the rest will require cryogenics, and that's where the problem may be with respect to using the carbon monoxide and oxygen gathered in the first step to run the energy requirements of the entire apparatus. If not, then perhaps it could be possible to use solar power.

The Perserverance rover now on Mars, is using a device called MOXIE, which gathers oxygen. I'm not familiar with how it works. That process may split off an oxygen atom from the naturally abundant carbon dioxide. If so, it will produce more carbon monoxide. That too could be used to run the gas separation apparatus. Otherwise, the carbon monoxide will be a waste product. Why not use that as a resource? After all, that's was in situ resourcing is all about.