Last year, NASA achieved something science fiction writers have been dreaming about for decades: It created oxygen on Mars. A microwave-size device attached to the agency’s Perseverance rover converted carbon dioxide into 10 minutes of breathable oxygen. Now, physicists say they’ve come up with a way to use electron beams in a plasma reactor to create far more oxygen, potentially in a smaller package.
The technique might someday not just help astronauts breathe on the Red Planet, but could also serve as a way to create fuel and fertilizer, says Michael Hecht, an experimental scientist at the Massachusetts Institute of Technology. But Hecht, who leads the oxygenmaking rover instrument, says the new approach still has a number of challenges to overcome before it can hitch a ride to our solar neighbor.
When Perseverance landed in Jezero crater in 2020, it carried the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE). The device draws in martian air, which is 95% carbon dioxide. By pumping a current between two oppositely charged electrodes in an electrochemical cell, MOXIE can split the carbon dioxide into carbon monoxide and oxygen ions. The oxygen ions then combine with each other to produce oxygen gas.
The experiment has been a successful proof of concept. But to work, MOXIE needs to pressurize and heat martian air—requiring extra parts that consume energy and make it bulky.
Vasco Guerra, a physicist at the University of Lisbon, thought a plasma reactor might be a better approach. A beam of electrons, accelerated to a specific energy level, can split carbon dioxide into its component ions, or plasma, just like MOXIE.
Moreover, a plasma reactor would be well-suited to the martian atmosphere, which is about 100 times thinner than Earth’s. Creating and accelerating a beam of electrons in the thin air is much easier, Guerra says. “There is an ideal pressure for plasma operation,” he says. “Mars has precisely this correct pressure.”
In the lab, he and his colleagues pumped air designed to match the pressure and composition of Mars into metal tubes. Unlike MOXIE, they didn’t need to compress or heat the air. Yet, by firing an electron beam into the reaction chamber, they were able to convert about 30% of the air into oxygen. They estimate that the device could create about 14 grams of oxygen per hour: enough to support 28 minutes of breathing, the team reports today in the Journal of Applied Physics.
Guerra’s team still needs to solve some practical problems, Hecht notes. To work on Mars, the plasma device would need a portable power source and a place to store the oxygen it makes, all of which could make it just as—if not more—bulky than MOXIE, he says. If space agencies were willing to spend millions of dollars developing it—as NASA did with MOXIE—the plasma approach could mature, Hecht says. He especially likes how the electron beam could be tuned to split other atmospheric molecules, such as nitrogen, to create fertilizer. “There’s nothing wrong with the plasma technique other than it’s a lot less mature [than MOXIE],” he says.
Science, 16 August 2022