It is possible that sometime this century the first human will set foot on Mars. If this happens it is then likely that those humans that do will want to stay there for a while. It takes between 150-300 days to get to Mars with current technology (depending on launch and vehicle variables), unlike the three days it takes to get to the Moon. Perhaps before we try to get to Mars we will have nuclear thermal propulsion, and the trip time will decrease to about 90 days. So extended missions will likely be the norm, and in fact there is talk about a permanent colony on Mars. This will be a tremendous technological challenge, which is one reason I think we should do it. I also think this should be an international project.

One of the many challenges is resources – a colony will need energy, food, water, atmosphere, and protection from radiation. Energy might be the easiest to solve – just use the nuclear engine that got you there. Food, water, and oxygen will likely be the most challenging, as Mars is far away to supply. It’s likely that we will send robotic missions to Mars to pave the way for any human crew, pre-supplying the mission with everything they need. But if the ultimate goal is a Mars colony we will need to figure out how to make it self-sustaining, and this means growing food. Plants not only provide food, they also can provide oxygen to breath. You can grow food hydroponically, but this is limiting. It would be easier to support a colony with soil.

Scientists, therefore, are very interested in how well the regolith on Mars will serve as a substrate for farming. We don’t have direct access to Mars regolith to study, but we do have information about what the regolith is like from the various landers and rovers we have sent to Mars. We can therefore simulate Mars regolith, at least to some degree, and see if we can grow plants in it. There have already been studies doing just that. A 2019 study looked at seed germination and plant growth for 10 crops in Earth control soil, NASA simulated Moon regolith, and simulated Mars regolith. They found that 9/10 of the plants (all but the spinach) germinated and grew well in the simulated regolith, although not as well as  in the Earth soil. Of note, the simulated regolith in this study contained added organic material, to simulate the compost from previous crops or food.

This is encouraging, but not the final word. There is now a recent study looking at three simulated Mars regoliths. They used material mined in Hawaii or the Mojave Desert, and a third made from scratch using volcanic rock and other material attempting to simulate as close as possible what we know about the chemistry of Mars. They studied two species, lettuce and the weed Arabidopsis thaliana, on the three simulated regoliths. Seeds germinated and grew in the two Earth soils but did not in the simulated Mars regolith made from scratch. The researchers interpreted this as – the closer you get the Mars regolith, the harder it is to grow plants.

They next added acid to the simulated Mars regolith because it was very alkaline, bringing the pH down to something more typical. Plants survived for about a week longer in this regolith, but still died.

The likely key is organic material. In the 2019 study organic material was added to the simulated regolith. In the Earth analogs in the current study, there would be organic material. In the fully simulated Mars regolith, this was basically crushed rock without organic material. So it’s pretty clear that adding organic material to Mars regolith is going to be critical in order to use it for farming. This does not seem like a deal-breaker – astronauts can compost any organic waste from their 3-6 month trip to Mars (if there is any) and their humanure can also be saved and treated if necessary to provide organic material. Sacks of compost can also be sent to Mars as part of the supplies. This will be necessary to bootstrap farming on Mars, but once that gets going, the soil quality should improve over time and more and more organic material will be broken down into it.

But problems with Martian regolith are not limited to what isn’t in the dirt, but also what is – most notoriously, perchlorates. These are highly toxic chemicals that make up 1-2% of the Mars regolith. They will likely prove toxic to any Earth plants we try to grow there. It’s possible to remove them, however. In fact, there are Earth bacteria that eat perchlorates which could be deployed.

The authors also note that Martian regolith is not homogenous – it differs in various locations on the planet. We may need to find a patch of Mars with the least terrible regolith to build our colony. Or, we could harvest the most crop friendly regolith on Mars and transport it to our station or colony (that would be much easier than brining it from Earth).

But any soil will likely have to be started with material from Earth and treated to remove anything too toxic.  But once even the slightest farming becomes possible it will likely get easier over time and organic material build up. Eventually we could have a self-sustaining farm on Mars. There is plenty of water on Mars so that is not an issue. Of course we are talking about a controlled enclosed environment. A farm that grows enough food to feed the people on Mars would create more than enough oxygen to breath. In fact, it would likely create too much, and some would have to be siphoned off to prevent a dangerous build up. This excess oxygen can then be stored for fuel.

Finally, we will need to choose crops that are best suited for the conditions they will face on Mars. However, we can then cultivate those crops to survive better, and may be able to genetically engineer crops with all the traits necessary to thrive on Mars.

The studies we have so far show that farming Mars will be a challenge, but one that can be overcome.