By: John Grant, Professor of Soil Sciences at Southern Cross University (Australia)
Along with advances in space exploration we have recently seen a lot of time and money invested in technologies that could enable efficient use of space resources. And at the forefront of these efforts has been a laser-sharp focus to find the best way to produce oxygen on the moon.
In October, the Australian Space Agency and the POT signed an agreement to send an Australian-made rover to the moon under the Artemis program, with the goal of collecting lunar rocks that could ultimately provide breathable oxygen on Earth’s satellite.
Although the Moon has an atmosphere, it is very thin and is made up mostly of hydrogen, neon, and argon. It’s not the kind of gaseous mixture that could sustain oxygen-dependent mammals like humans.
That said, there is actually a lot of oxygen on the Moon.. It just isn’t in a fizzy form. Instead, it is trapped within the regolith, the layer of rock and fine dust that covers the surface of this natural satellite. If we could extract oxygen from the regolith, would it be enough to sustain human life there?
The oxygen it can be found in many of the minerals in the soil around us. And the Moon is made up mostly of the same rocks you’ll find on Earth (albeit with slightly more material from meteors).
Minerals like silica, aluminum, and iron and magnesium oxides dominate the lunar landscape. All of these minerals contain oxygen, but not in a form that our lungs can access.
On the Moon, these minerals exist in a few different forms, including hard rock, dust, gravel, and stones that cover the surface. This material is the result of the impacts of meteorites that collide with its surface during countless millennia.
Some people call the surface layer of the Moon lunar “soil,” but as a soil scientist, I hesitate to use this term. Soil, as we know it, is something quite magical that only occurs on Earth. It has been created by a wide range of organisms working on the soil’s parent material, regolith, derived from hard rock, for millions of years.
The result is a matrix of minerals that were not present in the original rocks. Earth’s soil is imbued with remarkable physical, chemical, and biological characteristics. Meanwhile, the materials on the Moon’s surface are basically regoliths in their original intact form.
The regolith of the Moon is composed of approximately 45% oxygen, but that element is closely linked to the minerals mentioned above. To break those strong ties we need to put energy.
You may be familiar with this if you know about electrolysis. On Earth, this process is commonly used in manufacturing, such as to produce aluminum. An electrical current is passed through a liquid form of aluminum oxide (commonly called alumina), through electrodes, to separate the aluminum from oxygen.
In this case, oxygen is produced as a by-product. On the Moon, oxygen would be the main product and the aluminum (or other metal) mined would be a potentially useful by-product.
It’s a pretty straightforward process, but there’s a catch: it has a lot of energy. To be sustainable, it should be supported by solar energy or other sources of energy available in the Moon.
The extraction of oxygen from the regolith would also require considerable industrial equipment. We would first have to convert solid metal oxide into liquid form, either by applying heat or by combining it with solvents or electrolytes. We have the technology to do this on Earth, but moving this device to the Moon, and generating enough power to operate it, will be a great challenge.
Earlier this year, Belgium-based startup Space Applications Services announced that it was building three experimental reactors to improve the oxygen production process through electrolysis. They hope to send the technology to the Moon by 2025 as part of the European Space Agency’s In Situ Resource Utilization (ISRU) mission.
That said, when we do, how much oxygen could the Moon actually deliver? Well, it turns out quite a bit.
If we ignore the oxygen on the Moon trapped in the deeper hard rock material, and only consider the regolith, which is easily accessible on the surface, we can make some estimates.
Each cubic meter of lunar regolith contains 1.4 tons of minerals on average, including about 630 kilograms of oxygen. NASA says that humans need to breathe about 800 grams of oxygen a day to survive. So 630 kg of oxygen would keep a person alive for about two years (or a little longer).
Now suppose that the average depth of the Moon’s regolith is about ten meters and that we can extract all the oxygen from it. That means that the upper ten meters of the Moon’s surface would provide enough oxygen to sustain the 8 billion people on Earth for about 100,000 years.
This would also depend on how efficiently we are able to extract and use oxygen. Regardless, This figure is quite surprising!
Having said that, we have it pretty good here on Earth. And we must do everything we can to protect the blue planet, and its soil in particular, which continues to support all life on Earth without our trying.