Underground brine could be a source of oxygen on Mars

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If humans are never go visit March, they may well need to procure crucial resources during their stay, in order to survive long enough to explore and resupply for the long journey home. While the days of surface water flow are long past, the Red Planet is not entirely without raw ingredients to do this job.

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The March 2020 mission launched in July brings an experiment with exactly that goal in mind. MOXIE– the experiment of in situ use of the oxygen resources of Mars – is a box not much bigger than a toaster which produces oxygen from atmospheric CO 2 ~. While a much larger version would be needed to make liquid oxygen fuel for a rocket, MOXIE is sized to produce roughly the amount of oxygen an active person needs to breathe.

A new study led by Pralay Gayen at Washington University in St. Louis, Missouri, is testing a device that could tap into a different resource – perchlorate brine believed to exist in Martian soil in some places. The device can split the water in this brine, producing pure oxygen and hydrogen.

Perchlorate (ClO4) salts, as we have discovered, are common on Mars. These salts have an affinity for water molecules and can trap water vapor over time, turning into brine with a very low freezing temperature. There is proof of large amounts of what this brine might be below the surface of Mars’ north polar region, and smaller amounts have been cited as a possible explanation for the active streaks that sometimes appear on the Martian slopes.

To test if we could tap into this resource, the researchers built an electrolysis device that they used under conditions similar to those on Mars. It uses a standard platinum-carbon cathode and a special lead-ruthenium-oxygen anode that researchers previously developed. They mixed a plausible concentration of magnesium perchlorate brine and filled the free space in this vessel with pure CO.2 for an atmosphere similar to that of Mars. Everything was stored at -36 ° C (-33 ° F). When energized, brine flowed through the apparatus, dividing into pure oxygen captured on the anode side and pure hydrogen on the cathode side.

The device performed quite well, producing about 25 times more oxygen than its MOXIE counterpart can handle. MOXIE requires around 300 watts of power to operate, and this device matches that oxygen output to around 12 watts. In addition, it also produces hydrogen which could be used in a fuel cell to generate electricity. And it would be smaller and lighter than MOXIE, the researchers say. Ultimately, all of this just illustrates that MOXIE is working with a lower quality – but more widely accessible – resource of atmospheric CO.2 instead of water.

A device like this would of course have to undergo long-term stress testing to make sure that performance doesn’t degrade over time and is generally rugged. The membrane that separates the cathode and the sides of the anode has been handled with care to avoid CO2 fouling, for example. If your survival depends on a device you brought to Mars, malfunctions are not an option.

PNAS, 2020. DOI: 10.1073/pnas.2008613117 (About DOIs).

This story originally appeared on Ars Technica.


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