Successful O₂ production on Mars

The MOXIE instrument, weighing around 17 kilograms, was installed in the Perseverance rover and is now in use on the red planet. ©NASA/JPL

A performance like a small tree: The MOXIE instrument on board the Perseverance rover can reliably extract oxygen from the carbon dioxide in the Martian air under different atmospheric conditions, show the results from 2021. In seven test runs, the instrument achieved a rate of six grams of oxygen per hour . So far, the concept has proven to be successful. Larger plants could produce the gas for the breathing air of Mars travelers as well as for rocket propulsion on the red planet, according to the plan.

After the moon, Mars is the target of manned space travel: one day, the first human will set foot on the red planet. The numerous challenges include the supply of oxygen for the breathing air and the rocket propulsion on the return flight. Carrying the required amounts would be an enormous burden. So scientists are working on concepts to produce the gas on-site from the resources the planet provides. The "Mars Oxygen In-Situ Resource Utilization Experiment" (MOXIE) is dedicated to this goal: As part of the Mars rover mission Perseverance, it is being investigated to what extent oxygen can be obtained from the carbon dioxide in the thin Martian atmosphere by means of electrolysis.

CO₂ becomes O₂

The Mars rover, which has been on the planet's surface since February 2021, was equipped with an instrument about the size of a lunch box. It first sucks the Martian air, which consists of 96 percent carbon dioxide, through a filter to remove dust. It is then compressed and then passed through a device that electrochemically splits the carbon dioxide-rich air into oxygen ions and carbon monoxide. The oxygen ions then combine to form O₂. The MOXIE instrument records the quantity and purity of the gas. It is then released back into the Martian atmosphere along with the carbon monoxide.

As the developers report, the MOXIE instrument had to be designed as small as possible in order to accommodate it in the Perseverance rover. For this reason, the concept has so far been a test version that does not work continuously: the device is switched on and off for temporary experiments. This is done in a targeted manner under as different atmospheric conditions as possible, explains the team. "The Martian atmosphere is much more variable than Earth's," says lead author Jeffrey Hoffman of the Massachusetts Institute of Technology (MIT) in Cambridge. “The density of the air can vary by a factor of two over the course of the year, and the temperature can fluctuate by 100 degrees. So our goal is to show that the system works at all times,” says Hoffman.

Reliable even under fluctuating conditions

Since the rover's landing, the MOXIE instrument has been powered up seven times over the Martian year, each time taking a few hours to warm up and then another hour to produce oxygen before shutting down again. Each run was scheduled for a different time of day or night and for different times of the year. As the team now reports, the system has so far shown that it can easily cope with the changing conditions. With each run, the instrument met its goal of producing six grams of oxygen per hour - about as much as a small tree on Earth. "We're using resources on another planet's surface by chemically converting them into something that would be useful for a human mission," says Hoffman. "In this sense, the success is historic," says the scientist.

In concrete terms, the reliable oxygen production now shows the potential of the concept for manned space missions to Mars: "We have learned a lot that will help us with future systems on a larger scale," says co-author Michael Hecht from MIT. The researchers envision that an enlarged version of MOXIE could be sent to Mars ahead of a manned mission to continuously produce oxygen on the order of several hundred trees. At this capacity, the system should produce enough oxygen to both feed the people after they arrive and to power a rocket for the astronauts' return to Earth.

Testing of the MOXIE instrument in the Perseverance rover will now continue, the scientists say: they plan to increase capacity and increase production, especially in the Martian spring when atmospheric density and carbon dioxide levels are particularly high. "So we're going to set everything as high as we dare and let it run as long as we can," says Hecht.

Source: Massachusetts Institute of Technology, NASA, Article: Science Advances, doi: 10.1126/sciadv.abp8636

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