On the red and dusty surface of Mars, nearly 100 million miles from Earth,
an instrument the size of a lunchbox is proving it can reliably do the work of a small tree.
The MIT-led Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, has been
successfully making oxygen from the Red Planet’s carbon-dioxide-rich atmosphere since April 2021,
about two months after it touched down on the Martian surface
as part of NASA’s Perseverance rover and Mars 2020 mission.
In a study published in the journal Science Advances,
researchers report that, by the end of 2021, MOXIE was able to produce oxygen on seven
experimental runs, in a variety of atmospheric conditions, including during the day and night,
and through different Martian seasons. In each run, the instrument reached its target
of producing six grams of oxygen per hour — about the rate of a modest tree on Earth.
Researchers envision that a scaled-up version of MOXIE could be sent to Mars
ahead of a human mission, to continuously produce oxygen at the rate of several
hundred trees. At that capacity, the system should generate enough oxygen to both sustain
humans once they arrive, and fuel a rocket for returning astronauts back to Earth.
So far, MOXIE’s steady output is a promising first step toward that goal.
MOXIE’s oxygen production on Mars also represents the first demonstration of
“in-situ resource utilization,” which is the idea of harvesting and using a planet’s materials
(in this case, carbon dioxide on Mars) to make
resources (such as oxygen) that would otherwise have to be transported from Earth.
The current version of MOXIE is small by design, in order to fit aboard the Perseverance rover,
and is built to run for short periods, starting up and shutting down with each run,
depending on the rover’s exploration schedule and mission responsibilities. In contrast,
a full-scale oxygen factory would include larger units that would ideally run continuously.
Despite the necessary compromises in MOXIE’s current design, the instrument has shown
it can reliably and efficiently convert Mars’ atmosphere into pure oxygen. It does so by first
drawing the Martian air in through a filter that cleans it of contaminants. The air is
then pressurized, and sent through the Solid OXide Electrolyzer (SOXE), an instrument that
electrochemically splits the carbon dioxide-rich air into oxygen ions and carbon monoxide.
The oxygen ions are then isolated and recombined to form breathable, molecular oxygen, or O2,
which MOXIE then measures for quantity and purity before releasing it harmlessly back into the air,
along with carbon monoxide and other atmospheric gases.
Since the rover’s landing in February 2021,
MOXIE engineers have started up the instrument seven times throughout the Martian year,
each time taking a few hours to warm up, then another hour to make oxygen before powering back
down. Each run was scheduled for a different time of day or night, and in different seasons,
to see whether MOXIE could accommodate shifts in the planet’s atmospheric conditions.
The atmosphere of Mars is far more variable than Earth. The density of the air can vary
by a factor of two through the year, and the temperature can vary by 100 degrees.
So far, MOXIE has shown that it can make oxygen at almost any time of the Martian day and year.
As MOXIE continues to churn out oxygen on Mars, engineers plan to push its capacity,
and increase its production, particularly in the Martian spring, when atmospheric
density and carbon dioxide levels are high.
If MOXIE can operate successfully despite repeatedly turning on and off, this would
suggest that a full-scale system, designed to run continuously, could do so for thousands of hours.