# How do you 'make oxygen' on Mars?

This morning's BBC News says that a 2020 rover mission to Mars will "make oxygen". There is a brief line indication it will convert CO2. But no other details.

What process will the rover use? Is this a plausible method for obtaining oxygen on Mars for human life support?

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They are not "making oxygen", only stars can do that. They are separating one oxygen molecule from CO2, leaving CO and O. Do this twice and you have CO + CO +O2. That is, for every two carbon dioxide molecules you get two carbon monoxide molecules and one gaseous oxygen molecule. –  dotancohen Aug 1 at 16:56
@dotancohen I would encourage you to create an answer based on your comment, you might also want to indicate the probability of those now divided elements chances of reforming, and or the health risks of the carbon monoxide to human life. –  James Jenkins Aug 1 at 17:13
Well, even if that approach was used wholesale to make enough oxygen to support a manned base of some kind, there's plenty enough atmosphere to pump the CO into that I don't think you need to worry about Mars explorers dying of carbon monoxide poisoning any time soon. :) –  Michael Kjörling Aug 1 at 17:52
@JamesJenkins: There is no more of an answer to base on my comment! The extant answers address the 'how' already. –  dotancohen Aug 1 at 20:14

To be somewhat more specific than @geoff that gave an overview, regarding MOXIE (Mars OXygen In situ resource utilization Experiment), according to brief notice in the NASA press release that accompanied the Mars 2020 Rover scientific payload announcement:

The Mars Oxygen ISRU Experiment (MOXIE), an exploration technology investigation that will produce oxygen from Martian atmospheric carbon dioxide.

And a mock-up of the presumed layout of these announced scientific experiments and equipment:

An artist concept image of where seven carefully-selected instruments will be located on NASA’s Mars 2020 rover. The instruments
will conduct unprecedented science and exploration technology investigations on the Red Planet as never before. Credit: NASA

More detailed information will slowly trickle into the press as specifics are decided upon during the course of next few years, and indeed SpaceRef just published a story on it (I'd assume following media teleconference that was scheduled a few hours after yesterday's public announcement of the Mars 2020 Rover science package on NASA TV):

MOXIE -- short for Mars OXygen In situ resource utilization Experiment -- was selected from 58 instrument proposals submitted by research teams around the world. The experiment, currently scheduled to launch in the summer of 2020, is a specialized reverse fuel cell whose primary function is to consume electricity in order to produce oxygen on Mars, where the atmosphere is 96 percent carbon dioxide. If proven to work on the Mars 2020 mission, a MOXIE-like system could later be used to produce oxygen on a larger scale, both for life-sustaining activities for human travelers and to provide liquid oxygen needed to burn the rocket fuel for a return trip to Earth.

More on MOXIE in the article.

So this experiment is going to extract oxygen from the atmospheric carbon dioxide that constitutes 96% of Martian atmosphere. And the modus operandi for this particular experiment seems will be what Wikipedia describes as electrolysis of the atmosphere, possibly using zirconia as a catalyst:

$$\require{mhchem}\ce{2CO2} + \text{energy} → \ce{2CO + O2}$$

See e.g. Zirconia Electrolysis Cells for Oxygen Generation from Carbon Dioxide for Mars In-Situ Resource Utilization Applications. Additional note that carbon monoxide is merely an immediate reaction product and, while it could be used as fuel on Mars, it can also be further reduced by use of catalysts and additional energy into elemental carbon and oxygen, or by adding hydrogen by secondary Bosch reaction to graphite and water, and so on. Since it's not yet known exactly how MOXIE will do that, and what use its reaction products will be put to, I'd reserve further judgment on it for the time being.

There are of course also other possibilities to extract oxygen on Mars, for example from possible water ice pockets embedded deep into its regolith and using electrolysis to split water into oxygen and hydrogen, from dry ice that we know exists in abundance in Martian regolith and as a precipitate above it in polar regions and then using same or similar oxygen extraction methods as MOXIE will employ, to superheating and melting oxidized minerals, rust and metallic ore to release locked oxygen in it, and so on. But for the first steps, extracting it directly from atmospheric CO2 seems to be the easiest way to do it without needing to employ a whole truckload of machinery that we can't afford to land there, or don't really know how to yet.

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There are many proposed chemical processes that can lead to taking elements found commmonly on Mars, and using them to make more useful things for humans.

The entire process is vaguely know as In Situ Resource Utilization (ISRU)

That Wikipedia link nicely summarizes some of the likely approaches to be taken.

There was a great Sci Fi book that looked at the problem as a series of successive chemical processes, where the output of the first is used by the second, then third, so that they get a complete cycle going. Cannot find the reference. (There is an accident on earth, starts a fire, primary character cannot go due to lung damage).

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In simplest terms: You find a chemical that is made of a mixture of oxygen and anything else, and then cause the molecules of that chemical to give up their oxygen (and thus becoming something else).

2 H₂O can be cracked into 4 H₂ + 1 O₂ by electrolysis
2 CO₂ can be cracked into 2 C₂ + 2 O₂ by highly inefficient electrolysis, or via photosynthesis.
2 CO₂ can be cracked and recombined to 2 CO + 1 O₂ Hematite and Iron Oxide (both of which are common) can be (given enough energy) cracked to release the oxygen, and result in iron and oxygen.

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The process on MOXIE will convert 2 CO2 to 2 CO + O2 if I'm not mistaken. It has a carbon monoxide vent. –  dotancohen Aug 3 at 11:52