Simulated Mars soil can be packed together into a solid brick-like material — without needing any added ingredients to hold it together. That might mean real Martian soil could be easily used as a tool for building structures like habitats on the Red Planet’s surface, which could make human missions to Mars less complicated to pull off.
A group of engineers figured this out by using a high-pressure hammer to mash together material known as Mars soil simulant. It’s a collection of rocks from Earth that have the same chemical makeup as the dirt found on Mars, as well as grains that are of a similar shape and size as Martian grains. After working with the material for a while, the engineers found that just adding the right amount of pressure was enough to form the soil into tiny, stiff blocks — stronger than steel-reinforced concrete.
That’s not how we Earthlings make most of our construction materials. Typically, particles have to be mixed with a special type of adhesive, or binder, in order to stay rigid. The binder acts a bit like glue, holding the materials together and keeping them in a fixed shape. But the simulated Martian soil contains a special chemical ingredient that acts like its own innate binder. “It gives the soil strength when it’s compacted,” Yu Qiao, a structural engineer at University of California, San Diego, and the lead researcher on a NASA-funded study about this technique, tells The Verge.
Of course, simulated Mars soil is just that — simulated, and so its properties may not necessarily translate to real Martian dirt. But if they do, it’s good news for anyone dreaming of seeing people on Mars someday, since many experts agree that future Martian astronauts will have to use resources already on the Red Planet. People are going to need a lot of equipment to live on Mars and launching everything from Earth can get expensive and complicated. The more astronauts can “life off the land,” the less people have to rely on shipped materials. And these latest findings, published today in the journal Scientific Reports, suggest some buildings and structures could be made with Martian soil instead of Earth materials — and not much effort may be required.
“It’s really easy to swing a hammer on Mars,” Jon Rask, a life sciences expert at NASA who was not involved with the study, tells The Verge. “You can imagine a Mars explorer swinging a hammer to make strong building blocks.”
Before doing this study, Qiao and his team had actually been looking at ways to turn simulated lunar soil into building material — back when NASA was planning a return to the Moon. Unlike Mars dirt, lunar soil needs a binder to stick together, but the team wanted to come up with a way to use as little as possible. (The more binder you need, the more that has to be shipped up from Earth.) Typically, construction materials are made up of about 15 percent binder, according to Qiao. But through different compression techniques, the team was able to get the binder content down to 3 percent, while still making a strong lunar-based material.
Then in 2010, NASA shifted its focus from the Moon to Mars — so the team shifted its focus as well. “Our initial thought was: let’s borrow the success of lunar soil and see if it works on Martian soil,” says Qiao. And at first, that same compression process worked perfectly for the Mars soil simulant. Qiao and his team tried packing the dirt together with 6 percent binder, and immediately it worked great. So they decided to test the boundaries of what the soil could do and continued to pack the dirt together using less and less of the binder. “Then one day, I told my research assistant, let’s just compact the soil simulant itself,” Qiao says. “And it still worked.”
That made the researchers think there is some ingredient already in the Martian soil that helps it to stick together. They ultimately landed on iron oxide — a chemical compound that gives Martian soil its signature red color. When iron oxide is crushed, it can crack easily, forming fractures with very clean and flat surfaces, according to Qiao. And when these surfaces are firmly pressed together, they form super strong bonds.
Ultimately, Qiao envisions using Mars soil to build habitats or landing pads for vehicles that descend to the planet’s surface. He thinks the best way to make these structures is to do a form of additive manufacturing — where the soil is slowly layered. It’s the same way 3D printing works, and it could make it easier to build fairly large structures on the Red Planet.
But these bricks aren’t a complete solution to construction on Mars — at least not yet. The team only made miniature bricks, so it’s possible that larger Martian bricks won’t hold up so well. And it’s not clear how durable they are either, which is important for a few reasons. Obviously, you don’t want your structure to collapse. But less obviously, dust from the soil could break off into the air that astronauts are breathing, and inhaling large enough particles could cause health problems. The dust may also contain a type of salt known as perchlorate, which has been found throughout the Martian surface. Perchlorates can be toxic to human thyroid glands. So more research needs to be done to better understand these risks.
Still, many experts have been trying to figure out the best way to make Martian bricks for a while now. And before this study, many thought it would be an intensive process. There was talk of bringing some kind of heating device to bake the soil into bricks or even bringing microbes to Mars that could feed on human waste and create a binder material. But Qiao and his team have shown that you may not need all that much.
“What they’re doing is demonstrating proof of concept,” says Rask. “This is a good step for moving forward.”