Can Humans Live on Mars Without Earth’s Soil?

What's to come?
June 6 2013 8:38 AM

Our Guts May Hate Mars

We can leave Earth. But will we always have to bring it with us?

Twin Peaks, Mars.
Twin Peaks, Mars.

Courtesy of Timothy Parker/JPL/NASA

Eighty thousand people recently applied for a trip to Mars, an excursion that will allegedly be funded by selling reality-TV show rights for the voyage. The company running this curious venture, Mars One, estimates that the price tag for an expedition of four astronauts—currently slotted for 2023—would be $6 billion. But the ticket’s one-way: There is no budget for bringing them back.

It wouldn’t be a suicide mission, though. The travelers would be going as homesteaders, intending to make Mars their permanent home. If you’re going to have permanent colonies, say boosters of the idea, you might as well do it from the start.

It is not clear whether such a journey could be done safely for $6 billion, or at all. The hazards are numerous. Voyages to Mars will take anywhere between four and 10 months, depending on how much fuel you use. The lack of gravity will make the astronauts’ bones more brittle and prone to breakage. Zero gravity also changes the shape of the eye, harming some astronauts’ vision for reasons that are not fully understood—and in some cases, the changes appear to be permanent.

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But that’s just the start. Mars itself will be fantastically dangerous. The surface is bathed in solar and cosmic radiation. The temperature rarely gets above freezing. There’s omnipresent dust with toxic chemicals in it. There’s a total lack of breathable air. And if you have a serious medical problem, the nearest emergency room will be at least 34 million miles away.

But there’s another, more subtle hazard of Martian homesteading that people have barely begun to think about: the lack of soil. It may be hard to keep people healthy in the long term on Mars without Earth-made soil. Lots of it.

During the Humans to Mars conference held in Washington, D.C., in May, several panelists suggested that colonists would grow food hydroponically, in water. That seems logical: Shipping soil from Earth would be expensive, and we’d have to assume until proved otherwise that using Martian soil would be dangerous, because it has a different chemistry than Earth’s. (For example, it has perchlorates, chlorine-based salts that are known to harm the thyroid.) So for the foreseeable future on Mars, hydroponics seems to be the way to go.

You can grow a reasonably good tomato in water. But soil is a whole ecosystem, containing bacteria, protozoa, nematodes, insects, and much more—and it supports us in many ways.

For one thing, soil bacteria appear to be important for maintaining the proper diversity and balance of microbiota (i.e., bacteria) in the human gut. Scientists say that the bacteria and tiny insects in soil provide ecosystem services to humans and everything else on the planet. They break down the dead and the discarded, purify water, and cycle carbon dioxide into and out of the atmosphere.

Justin Sonnenburg, a microbiologist at Stanford, says that soil bacteria also enhance the quality of the foods grown in it. For instance, some of the microbes attack the plants. That may sound like a bad thing, but in fighting off those assaults, the plants generate compounds that are beneficial to human health, such as antioxidants. What it comes down to is this: Among other functions, good soil has bad bacteria that make plants do good things. We may be able to replicate some of these functions with technology, but if we don’t know all of the things that soil does, we may miss something important.

Martian colonists could probably live for years on food grown without soil. The question is, could they live on it for decades? Could their children grow up on it? Are there hidden hazards that would not become apparent until much later? To put these questions another way: Can we identify and reproduce the ecosystem services of Earth for a lifetime?

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