This is a transcript of the Gastropod episode, Potatoes in Space, first released on April 23, 2019. It is provided as a courtesy and may contain errors.

WIEGER WAMELINK: There’s quite some difference. Especially with the moon. The moon soil is very coarse. It’s very sharp. And that’s one of the very important differences not only for the plants but also for the worms. Because they eat soil and if you eat soil and it’s sharp, it’s the same as if we would eat broken glass.

NICOLA TWILLEY: Oh man, those poor little wormies! But why are we feeding worms moon soil exactly?

CYNTHIA GRABER: How do scientists even get soil from the moon in the first place? Sure, we need to study it if we’re ever going to grow food in outer space, but where does this crushed moon rock come from?

TWILLEY: Guess what, you’re listening to Gastropod, the podcast that answers these kinds of questions because it’s the podcast that looks at food through the lens of science and history. And this episode is all about space farming. I’m Nicola Twilley.

GRABER: And I’m Cynthia Graber, and space farming sounds like it’ll be pretty challenging. Why bother in the first place? Couldn’t we just bring along all the nutrient-rich slurry we’d ever need to keep us alive?

TWILLEY: Oh sure, and have you moan how boring that slurry tastes for the rest of all time.

GRABER: True.

TWILLEY: But how about algae—could we survive on that? I feel like that’s what they do in the movies.

GRABER: That sounds about as tasty as a beige food replacement. But if we do decide to grow food, how will we do it? Would we even need soil? How would it work?

TWILLEY: We have so many questions. And this episode has so many answers. It’s the how, what, and why of farming in space, including the all-important question: what difference does any of this make for those of us who aren’t heading to Mars anytime soon?

GRABER: Plus, are any of your favorite sci-fi flicks doing space farming right?

TWILLEY: Well, and let’s not forget the worms. Do the worms make it?

PRE-ROLL

STAR TREK CLIP

TOM: Tomato soup.

COMPUTER: There are fourteen varieties of tomato soup available from this replicator. With rice, with vegetables, Bolian-style, with pasta—

TOM: Plain.

COMPUTER: Specify hot or chilled.

TOM: Hot! Hot, plain tomato soup!

WAMELINK: I’m also a science fiction fan. So a bit of a Trekkie.

TWILLEY: This is Wieger Wamelink. He’s an ecologist at Wageningen University in The Netherlands. And although he’s a Star Trek fan, he’s also a scientist, and he is sadly all too aware that the replicator is still firmly in the realm of science fiction.

GRABER: So unfortunately, no, we can’t just order whatever dish we want and have it magically or even scientifically appear for us. But why not just bring dehydrated tomato soup with us?

WAMELINK: Well, packing and bringing it is of course an option and in the first years that will be the main way to get yourself nourished. But it costs a lot of space and energy to get all that food up there especially when you go to Mars. That’s totally inefficient. So if you want to stay there for a longer period then you have to grow your own crops over there.

TWILLEY: Tomato soup flakes in a foil pouch—that’s fine for a three-month stint on the space station, where you can get resupplies. But you wouldn’t want to count on it on Mars.

WAMELINK: If something goes wrong then you have nothing to eat. And. Well when you’re on the moon you could survive that because it’s only a two day travel, but if you’re on Mars it’s at least six months. And it could be twice as long. You won’t survive.

GRABER: But even if we could bring all the food we needed with us, even if the weight wasn’t a problem, something else happens to food over time. It breaks down, the vitamins and the nutrients in the food start to decompose and it’s not as nutritious as it once was.

GIOIA MASSA: And this isn’t a problem right now, because we’re on the International Space Station. We were getting regular supplies of food from Earth. So the astronauts are not at any risk for nutritional degradation.

TWILLEY: This is Gioia Massa. She’s a plant scientist with NASA at Kennedy Space Center.

MASSA: It won’t take five years to do a Mars mission, but we may have to send the food ahead of time. Which means that the food the astronauts might eat, maybe on the return journey to Earth, could be five years old. And right now we don’t have food that will last that long and still maintain all of the dietary requirements for the crew.

GRABER: These are incredibly practical reasons as to why we might need to grow food in space. But here at Gastropod, we love food for not just its practical side.

ESTHER MEINEN: What we know from people who work in space that they really like to have something fresh in their mouth. Something crispy, something with a texture. Something with taste because they are losing their taste.

TWILLEY: This is Esther Meinen, she’s another of our space farmers this episode. And she’s a colleague of Wieger’s at Wageningen University, where she works on space greenhouses. Esther’s point is that in space, food has less flavor—mostly because your face swells up—astronauts call it space face—so your taste buds and your sense of smell both suffer.

MEINEN: So of course they take food but they really miss fresh food.

WAMELINK: And we know that the astronauts in ISS, they lose weight.

GRABER: They lost weight partly because they’re losing muscle mass in space. But also, they don’t always feel like eating the food they have. Not just because they can’t taste the flavors as well, also because the food isn’t great.

TWILLEY: The website Eater had two famous chefs—David Chang and Traci des Jardins—try some space food—David got crawfish étouffée, which sounds promising, and Traci got tofu with hot mustard sauce, which I thought was pretty avant garde for NASA

EATER CLIP

DAVID CHANG: Tastes like I’m in space or prison.

TRACI DES JARDINS: Wow, that’s pretty bad. I wanna spit this out.

CHANG: Everybody taste this.

DES JARDINS: C’mon, try.

GRABER: So, no, NASA’s space food was not a big hit with the chefs.

TWILLEY: So the food sucks, you can’t taste it anyway, and frankly, it’s hardly a tropical vacation up there in space.

WAMELINK: It’s harsh. And if your food consists of energy bars or the food the astronauts now get on ISS, there is no fun in eating it.

TWILLEY: Whereas a real lettuce leaf or a real tomato? That’s going to be a lot more fun to eat. And it’s going to taste a ton better. I mean, that’s true even here on Earth.

WAMELINK: And that helps because well you feel you yourself much better and, yeah, there will be less tension between the astronauts as well if there is something to enjoy. So there’s more than just the nutrients that you need.

GRABER: If you’re all sitting down together to a real meal of real, tasty food, it might be easier to get over cabin-fever inspired arguments or irritability. And Gioia says there may be even more mental health benefits if the astronauts are growing the tomatoes themselves.

MASSA: There might be some psychological benefits of growing plants, of caring for plants, using plants to help mark the passage of time.

TWILLEY: So plants make food we can eat, and they make us happy and less annoyed and less annoying to others. But all those reasons are not the reason why we humans first looked into taking plants into space.

GRABER: Ray Wheeler is a colleague of Gioia’s at NASA’s Kennedy Space Center in Florida. He’s been studying how to farm in space for 30 years. But American researchers started to look into growing plants in space in the 1950s, even before NASA was founded.

RAY WHEELER: So at that time the U.S. Air Force began to sponsor some studies looking at algal systems to produce oxygen, primarily for their oxygen production for space travel.

TWILLEY: Algae! I knew it was the answer! Although it seems as though it was chosen less for taste reasons than to help us breathe.

WHEELER: And so they grew very rapidly. They could generate a lot of oxygen in, you know, relatively small volume.

TWILLEY: Back in the 1960s, biologist Joe McClure became the first man to spend a full day breathing algal oxygen. He actually spent 26 hours in a sealed tank at Boeing’s Life Support Systems research center in Seattle, surviving entirely on the oxygen burped out by fluorescent green tubes full of chlorella, which is a single-celled algae. Apparently, the air in his tank smelled like wet hay, but he emerged hale and hearty.

GRABER: Chlorella went into orbit before humans did—it even went to the moon before humans, thanks to the Soviets. And it seemed to do just fine in space.

LAUNCH SOUNDS, SPUTNIK BEEPS

ALGAE BUBBLES

GRABER: That’s the happy sound of algae in space, bubbling out oxygen for astronauts! Okay, so then the scientists wondered, if algae thrived and provided all that great o2 to breathe, couldn’t we also eat it?
TWILLEY: Well. According to a 1961 Time Magazine article about Joe McClure’s algae tank adventures, a Boeing scientist’s daughter had managed to make quote “acceptable” cookies from the chlorella. But ultimately, Ray Wheeler says we’re not going to want to survive ONLY on this stuff, for sure.

WHEELER: The types at least that they were using there they weren’t all that palatable. And if you have a high percentage of it in the diet, it’s not the right balance of nutrients.

WAMELINK: Algae. Yeah. You can make something of it but it’s totally different from a potato. And. Well, if I’m there and it’s already harsh then I would prefer a potato above some algae soup.

TWILLEY: I’m with Wieger here. And growing a potato in space, we all know that’s possible.

THE MARTIAN CLIP

MARK WATNEY: They say that once you grow crops somewhere, you’ve officially colonized it. So, technically, I colonized Mars.

GRABER: Matt Damon, I mean Mark Watney, he figured out how to grow potatoes on Mars. So can we do it? What do real live scientists have to get right to make it work?

TWILLEY: And are potatoes specifically really the way forward? I mean, I love a good potato, but is that what scientists actually think we should grow in space?

GRABER: Turns out, the answer to that question has changed over time.

WHEELER: One of the various earliest recommendations or meetings that discussed what types of crops to use was held at Wright-Patterson Air Force Base in the early 1960s, and they focused largely on salad type crops.

GRABER: After algae, the newly formed NASA started looking into slightly more complicated greens, like lettuce. But the Russians had bigger plans. They imagined full-on planetary colonies.

WHEELER: They really began to think more about field crops and staple crops. So grains like wheat and rice, potatoes.

BIOS TAPE (IN RUSSIAN WITH VOICEOVER)

VOICEOVER: BIOS-3, or the Biological Support System, is an experiment which was started in the early sixties of the last century. The idea was very simple and consists of an attempt to create a prototype of a future station on a different planet, for example, on the Moon or on Mars, outside the biosphere.

TWILLEY: That’s Egor Zadereev, Senior Research Scientist at the Institute of Biophysics, taking a Russian TV channel on a tour of the formerly top secret BIOS facility in Siberia.

GRABER: In the 1970s, the Soviets sealed two or three bionauts in the system for months at a time. They grew wheat, soy beans, salad leaves, carrot, radish, beets, potato, cucumbers, cabbage, onion, and, of course, some algae. And apparently the system was able to provide 100 percent of the oxygen they needed and more than half the food. One of the bionauts was nicknamed the “Siberian Martian” after spending a total of 13 months inside BIOS-3.

TWILLEY: NASA did not want to be outcropped by the Soviets. So they started testing soybeans, and sweet potatoes, and yes, also potato-potatoes!

GRABER: But we’re no longer fighting the Cold War in space, and we’ve scaled back our ambitions quite a bit since the 70s and 80s. No more staple crops for self-sufficient lunar colonies.

WHEELER: The thinking is now you know well let’s not go too far off with our research in terms of planetary colonies and things. What can we do in the near term and now we’re really focusing again on salad crops.

TWILLEY: Which is why NASA is back to lettuce again. Part of this is that on the space station, astronauts don’t have the facilities to cook something like a sweet potato. Or even clean their veggies when they harvest them. It’s not like you can put them under the tap.

MASSA: So lettuce was one that had pretty low microbial counts on the leaves when it was grown in our system, and we knew it would be safe to eat without much cleaning or any cleaning.

GRABER: How easy it is to clean the plant is important. Also the nutrient content is important, too. Gioia says the folks at NASA have chosen red lettuce over green, because it has a particular type of plant chemical that could help repair the DNA damage astronauts get from radiation in space.

TWILLEY: Lettuce is also great because you can eat pretty much the whole plant, so there’s not a lot of waste. That’s something Esther prioritized when she was designing a prototype greenhouse for the international space station.

MEINEN: So we did a plant selection for that. And we chose species and crops with good taste like radish and herbs. They really like the herbs. Just to have something fresh.

GRABER: Radishes are kind of spicy, which is great because, as we said, your sense of flavor is dulled in space. Plus you can also eat the leaves.

TWILLEY: And of course, whatever you plant in space has to grow pretty quickly, and pretty easily. Esther actually tried an experiment to grow strawberries in a simulation of the space station

MEINEN: And the germination was really really hard. A low germination rate. Plants were growing very slowly so it took me let’s say three, four months and then I had some small plants. So that is taking too much time. So we decided to stop with that.

TWILLEY: No strawberries in space. Already I’m questioning whether I even want to go.

GRABER: I signed out of this mission a long time ago. Too claustrophobic. But so these radishes and lettuces and herbs might be great on the International Space Station. But that won’t be enough to keep us well fed once we’re colonizing Mars.

WAMELINK: So that means that potatoes are becoming very important because forget about quinoa or whatever superfood you hear of, it’s potato. Lots of energy, lots of essential nutrients you need. And in that perspective The Martian was very good, the movie, that they grew potatoes, because that is what you need. You need a lot of energy.

TWILLEY: Wieger actually tried growing quinoa in his space simulation and he couldn’t get it to form seeds at all. So really, Matt Damon slash Mark Watney was right. Potatoes are it.

THE MARTIAN CLIP

MAN: You could teach all this in a class someday.

WATNEY: You know, the good stuff, like how to make a bathroom using NASA tubing and an old RTG. How to cook a potato about 6,000 different ways. The Mark Watney syllabus.

GRABER: But there’s something that The Martian got wrong as Mark Watney was growing his potatoes—he was growing them in basically the Martian equivalent of a greenhouse, and you can see light shining in from the outside.

WAMELINK: And that’s not going to happen. You see that a lot.

TWILLEY: The problem here is radiation. We’re protected from space radiation here on earth by our atmosphere. But the atmosphere on Mars is so thin that it isn’t up to the job.

GRABER: And space radiation is really dangerous—as I said, it damages astronauts’ DNA. It can give you cataracts and harm your skin, it can lead to cancer, it can harm your nervous system, give you digestive and blood issues, basically everything bad.

WAMELINK: Toxic radiation is not blocked by glass or plastic or whatever you want to use. So not only we will suffer from it, but also the plants.

TWILLEY: Wieger told us that Matt Damon and his potatoes both would have been totally screwed. What Matt should have done—and what space scientists think we’re going to have to do on Mars—is go underground.

WAMELINK: An older movie I really liked is Total Recall.

TOTAL RECALL CLIP

WAMELINK: …because that’s quite correct on how it’s going to be. They live in old lava tubes. One of the ideas is that we should find them on Mars and go live in there, because then you’re also protected from the radiation.

GRABER: There’s another problem caused by that incredibly thin atmosphere. Mars has much less atmospheric pressure than Earth and it’s also much colder, and both of these are related to that thin atmosphere. Water on the surface would either evaporate or freeze. So, the long and short of it is, we and our plants are going to have to be very well protected and probably underground.

TWILLEY: As it turns out, plants are actually a little bit better at dealing with the rigors of space than we are.

WAMELINK: Plants can be grown under low pressure. And NASA have done experiments, I know, that they even can go to 10 percent of what we have in which we cannot walk or survive. But the plants can.

TWILLEY: It actually makes sense that plants are tougher than us, because we can move to better conditions using our legs, and they can’t really. But still, Wieger’s point is, we have to build underground bubbles for our own survival, so we can build bubbles for our plants too.

GRABER: One question that Nicky and I both were wondering about has to do with gravity. So here on Earth, plants grow up, their roots grow down.

TWILLEY: Except in Australia. Just kidding.

GRABER: Right. Anyway. They’re obviously getting lots of cues that tell them how to grow, but doesn’t gravity provide a really important one? How will plants grow without Earth’s gravity pulling their roots down?

WAMELINK: So it’s very difficult to test on Earth.

TWILLEY: Because Earth’s gravity is hard to escape. Space agencies have ways of simulating lower gravity situations—you can strap astronauts into one of those horrible fairground type rides that spins you around till you vomit. Or you can go up in a plane (a plane they literally call the Vomit Comet) and do big loops.

GRABER: But you can’t send a plant into those zero gravity rides or on those planes—imagine what would happen to all the soil! But scientists have actually been growing plants in spaceships, and those plants do in fact grow in zero gravity.

WAMELINK: So we know that it works on the zero gravity so I can’t imagine that it wouldn’t work on Mars or on the moon.

TWILLEY: Once again, it seems as though plants actually have a little bit of an edge on humans when it comes to adapting to low or no gravity.

MASSA: In the absence of gravity, plants just go to all those other senses. You know, they’re looking at the light, they’re sensing the water and the moisture and the oxygen levels and things like that. And then they give these, these pretty good integrated responses.

GRABER: Obviously it’s not easy to tweak everything just right to tell the plants how to grow. One thing scientists had to figure out is that it’s not just any light that plants grow towards, it’s actually blue light they need to figure out what direction is “up.”

TWILLEY: This is where things start to get really interesting. Because to you or me, light seems like it’s just light. But actually, sunlight is a specific strength and spectrum and that matters.

GRABER: Throughout our history as humans, we’ve had it pretty easy. We have this big glowing orb in the sky, and it’s strong, and plants are fully adapted to thrive in it. But indoor lights have historically been really weak in comparison, certainly not strong enough to grow plants indoors.

TWILLEY: Fortunately for space farmers, lighting technology has really come a long way in the past few decades—nowadays, we all have LED bulbs in our houses, and that’s really recent.

GRABER: LEDS are much much stronger than incandescent light bulbs, and so it’s actually possible to grow plants under them.

TWILLEY: The first LEDs were invented in the 20s, but they were pretty low-intensity and only available in red and of course super expensive. Ray told us that NASA started experimenting with early versions of red and blue LEDs in the 1980s.

GRABER: As the decades went on, LEDs eventually improved and got a lot cheaper, and they covered the full visible spectrum—

TWILLEY: To the point where LEDs could be used commercially for indoor farming. And where did that first happen, you might ask? Well, exactly the place we visited for this episode: the Netherlands.

MEINEN: It’s a leader in the world. We are a leader in the world. Yeah.

GRABER: The Netherlands is small. It’s the size of my home state of Maryland. But it is covered in high tech greenhouses and as a result, it’s the world’s leading exporter of tomatoes and potatoes and onions…

TWILLEY: All those billions of Dutch tomatoes taste of literally nothing, mind you. But they do grow a lot of them on a tiny amount of land. The Netherlands are the second largest exporter of food after the US. And a lot of that is because they are masters of artificial light.

MEINEN: And with light you can do more. You can steer the crop. You can make the days longer. So when you have lamps you can cultivate year round.

GRABER: Esther’s an expert in lighting for greenhouses. But a few years ago, her expertise was tapped for agriculture pretty far away from those Dutch buildings. Eden ISS: a ground-based demonstration for space ag.

MEINEN: It was a project for four years and last year we produced fresh food on the South Pole. So it was very nice.

GRABER: OK, so what does a prototype greenhouse for space look like?

TWILLEY: Well, picture a shipping container. It sat next to the German Antarctic research station, the Neumayer Station. It’s on stilts, so that it doesn’t get buried in snow. And a German technician called Paul made the short trek over to tend the plants every day.

MEINEN: Half of it is for cultivation of the plants. So you have a corridor and on two sides we had two to four layers of crops with different shelves. We also had a part where it was the computer and where Paul could look outside to the penguins.

GRABER: Whenever Paul stepped inside Eden ISS from the frigid South Pole air, he of course would quickly feel warmer. And his eyes would have to adjust, too, because the light inside was glowing red. For the plants.

TWILLEY: The precise color and intensity of that light—that’s all Esther’s research.

MEINEN: We have lamps where we can choose the spectrum. 10 years before we could not do that. And now we can give the spectral quality that we want to give. But now is the question: What is the best spectrum for crops?

GRABER: Light might look clear to you, or even maybe you think it’s white, but actually it’s all the colors of the rainbow and beyond. The spectrum emitted from the sun covers from ultraviolet to infrared and everything in between. And plants use different colors, different wavelengths, for different purposes.

MEINEN: When we first started, we gave a lot of red and blue. Because from the red we know it’s good for photosynthesis. Blue they need a little bit for the stomates to open. But now we realize that just giving red and blue is not enough.

TWILLEY: This is totally fascinating research—Esther and her colleagues do experiments where they give a little extra green light, say, and see what that does to their seedlings. They’re finding that with different light recipes, plants grow in different shapes, flower at different times, produce more or less vitamins—they can even taste different.

GRABER: There’s a lot that scientists are still figuring out. Before Esther realized that strawberries took too long to grow in space, she was trying to use light to make a super strawberry that has more vitamin C.

MEINEN: We tried it. We tried to give more red light in strawberry and we saw more vitamin C. But at the end it was not just because of the red light but just because we gave more light. So yeah.

GRABER: And just giving it more full-spectrum white light, well, that takes too much energy. It’s just not worth it. Scientists are trying to conserve energy overall, so they’re trying to figure out just what colors of light the plants need and provide just that perfect recipe.

TWILLEY: What’s also kind of a challenge to this whole idea of a perfect light recipe is—what are you actually going for? What does optimizing your light recipe mean?

MASSA: “Best” could mean the biggest plant with the most food. OK well that one makes sense. But what about the most nutritious plant? Well maybe that’s what you want, too. Or what about the most delicious plant?

GRABER: So far, Esther has been defining her success by yield. Not all plants like the exact same spectrum, but she says she can get a twenty percent increase in yield, at least for the plants she’s growing in Eden ISS, by tweaking her light recipe.

TWILLEY: So after three years of research, EDEN ISS went to the South Pole. And all winter long—which at the South Pole is about 9 months—Paul the technician grew veggies.

GRABER: And by the end, Paul had harvested about a third of a ton of lettuce and herbs and radishes. Not a bad haul.

MEINEN: Yeah they were very happy. They were so happy. Because in the Neumayer it was the first time they had fresh food. And they want to continue. They really loved it and especially the herbs.

TWILLEY: EDEN ISS was a proof of concept. It was at the South Pole, which is harsh, but not as harsh as Mars. And the idea was to just show we could grow some fresh food to perk up an astronaut’s diet on the space station, not actually provide all their food needs.

GRABER: That’s why the scientists chose crops that could be grown hydroponically, without any soil. But what if you want to grow more substantial crops like potatoes to feed a new Martian or lunar colony? It is possible to grow potatoes in water, but they grow much better in dirt.

TWILLEY: Plants on earth love soil.

WAMELINK: Well yes soil on earth is very important. Without soil there will be no life. Absolutely none. Plants grow in it. Our food grows in it. The bacteria we need grow in it. The fungi. So it’s essential. No soil, no life.

GRABER: But we are clearly not bringing Earth’s soil with us to a space colony. So what about the soil on the moon or on Mars? Could plants love that soil, too?

TWILLEY: That’s exactly what Wieger wanted to find out. So he did an experiment. And we ate the results. Which we’re going to tell you all about. But first.

MID-ROLL

WAMELINK: We came up with the idea—well, I actually came up with the idea—to look if in principle plants we have here in the Netherlands, if they could grow on Martian or moon soil. And I found out first that nobody ever tried this. And second that NASA has special simulants that represent Moon and Mars soil.

GRABER: These Mars and moon soil simulants sound fascinating. But how does NASA know what Martian and lunar soil is even like?

TWILLEY: NASA has actually brought back soil from the moon. During the Apollo days, we brought back nearly half a ton of material from the surface of the Moon. It’s weird stuff.

WAMELINK: Well you can’t even call it soil but something like looks like soil can be formed on the moon is because of the radiation that comes from the sun. That radiation breaks down the rocks in a very, very slow process but in the end you turn with something that looks like soil. But since there is no wind, there is no water, it just falls apart.

GRABER: And so even though it looks kind of like Earth’s soil, that crumbly stuff from the moon is incredibly coarse and sharp. But the point is, we have samples, we know what it’s like.

TWILLEY: On the other hand, we haven’t brought back any soil from Mars because we’ve never brought anything back from Mars. Of course, rocks from Mars have landed on Earth, as meteorites, but they burn up in the atmosphere so you can’t use them as a good guide.

GRABER: But you all might have followed along with the exciting travels of Spirit, or Opportunity, or Curiosity, the most recent Mars Rover. We’ve landed a handful of probes on Mars, and those probes have sent back information about the soil. Or, I should say, soils.

WAMELINK: On Mars there is also more variation in the soil type. We know now. Because Mars had water in the past and there is still weather, there is wind. So there are more types of soil.

GRABER: There are a couple different Martian soil simulants available, and Wieger ordered one.

TWILLEY: Wieger showed us some of this Mars soil simulant and Moon soil simulant, and they actually look quite different from each other. The Moon soil is this flat grey color, very coarse, like Wieger said, and sharp looking.

GRABER: And the Mars soil is, yes, red. Or kind of a reddish brown. And that’s because there’s basically rusted iron in it.

TWILLEY: If you’re like me, right now you’re thinking, I want some Martian soil. Like Wieger.

WAMELINK: You can just order the soils on internet—how easy it is. It’s quite expensive, I must say, you pay two and a half thousand dollars. Yeah about that for 100 kilos. So it’s not cheap but well then you have it.

GRABER: Originally NASA made the first batch of simulated soil, but now it’s made by contractors and labs, and some of it, yes, you can order on the Internet. But even if we know what it is, how in the world is anyone making Martian soil here on Earth?

TWILLEY: Well, Cynthia, it’s perfectly simple. You start with Earth rocks that are as close as possible to Martian soil. There a couple sites—one’s in my backyard, in the Mojave Desert.

WAMELINK: This one actually comes from a volcano on Hawaii. And the moon soil comes from Arizona from a desert. And what I did is purify it. So there’s no organic matter in it anymore which makes sense because well there is no organic matter on Mars.

GRABER: But just getting the right type of rock, the one closest to the moon and to Mars, that’s not enough. They have to get the texture right, too.

WAMELINK: They spread it out on the floor of one of their huge buildings and then just drove over it to break it, because they had to have those sharp edges on the soil.

TWILLEY: And hey presto! Moon soil simulant, here on Earth. So, lots of scientists use these simulants, to test rover tires and other instruments. But Ray Wheeler told us that Wieger was right—no one had used them to grow plants.

GRABER: This is partly because they didn’t think it’d work. They thought that that coarse, sharp soil would puncture the roots of the plants.

WAMELINK: And to make it even worse, it’s both on Mars and on the moon, there are lots of heavy metals in the soil. Well and the plants don’t bother. But we do. There is zinc, Cadmium, lead, Mercury and all those things can make you sick.

TWILLEY: And because no one had tried to grow plants in Martian or lunar soil, no one knew if the plants would take up heavy metals in those conditions. If they grew at all in this weird soil.

GRABER: There was only one way to find out. Wieger got online, ordered his soil simulants and planted a bunch of plants.

WAMELINK: We had only four crop species in the first experiment and a lot of wild plants because the idea was they are much tougher than crops so they’re likely, more likely to survive.

GRABER: And Wieger planted a lot of plants, far more than he usually would for a conventional agriculture experiment.

WAMELINK: Normally you don’t do that because you don’t need it. But we thought, “Well, difficult soil… so let’s do a lot of replicas, maybe something will germinate.”

TWILLEY: But, much to Wieger’s surprise, basically everything grew.

WAMELINK: And some of the seeds, for instance rye, germinated already within 24 hours. Garden cress as well. And we didn’t even have the forms ready to fill in the scores. So we had to do it very fast and it was amazing lot of work.

GRABER: All that extra work was great news—obviously the soil’s sharp edges weren’t killing the plant roots.

TWILLEY: But Wieger was still worried about the heavy metals, so he tested them and he discovered the plants didn’t take those metals up.

WAMELINK: So that’s quite good. Otherwise you couldn’t eat them. I could grow them but you can’t eat them, so that doesn’t help then, hey, if you can’t eat them. LAUGHS

GRABER: Okay, one bullet dodged.

TWILLEY: Once Wieger had caught his breath from that frantic first experiment, he decided to focus all his attention on crops. Like he said, he grew a few crops in his first experiment alongside the wild plants. But they didn’t really give him a harvestable yield. In fact, they were pretty tiny, because he was just using the lunar or Martian soil plus water, no nutrients or fertilizer.

GRABER: But for the second experiment, Wieger decided to enrich the soil, just like people would probably do on Mars. He pretended that he was plowing in those first plants, uneaten, so they could become compost for the next harvest.

WAMELINK: And then we were able to harvest radishes. We had beans, we had tomatoes. Well let’s say, about a small coin size, but we had them.

GRABER: The third crop, Wieger went all out. He planted potatoes, and peas, and tomatoes again. And this time, he added not just plant compost, but the equivalent of what we might be mixing in ourselves on Martian or lunar colonies.

WAMELINK: We manured it a bit, as if we were using the… feces of the astronauts.

GRABER: One more thing that Mark Watney got right on Mars.

THE MARTIAN CLIP

TWILLEY: Gross but effective. On Earth however, developed countries have all sorts of rules about using human feces to fertilize crops. Fortunately, the Netherlands has more pigs than people in some places, which means there’s a lot of pig poo. Which Wieger used.

WAMELINK: And then we got a really big harvest—much more than we anticipated. We had that much green beans that we didn’t know what to do with it. And the tomatoes they were growing in the greenhouse, but they were growing that fast that we had to cut them on top—otherwise they would have grown out of the greenhouse.

GRABER: Much to everyone’s relief, Wieger is moving away from pig poop in his next round of experiments. He’s using purified urine from the people of Amsterdam.

TWILLEY: And he’s got another soil enhancement trick

WAMELINK: Well we need the worms.

TWILLEY: The worms! They’re back! But there’s a problem. Remember, the soil is really sharp, especially moon soil. And worms chew on the soil, so Wieger was worried it would tear up their insides.

WAMELINK: We tested it. The worms survive in the soil so they can handle it. It’s very tough of them.

GRABER: Worms in space!!!!! I’ve wanted to say something like that this entire episode.

TWILLEY: So yeah, it turns out worms and plants are better at space than us. Hell, pigs probably are too. In his office, Wieger had set up some worms in a glass terrarium filled with Martian soil. He added some dead plants to the top of the soil and then sowed some tomatoes and basil, and then left it for a year.

GRABER: Down at the bottom of the terrarium, we could see just the standard reddish brown crumbly Martian soil simulant. But things got more interesting where the worms had set up their homes, near the surface.

WAMELINK: And in the upper layer, well, it’s a bit brown and it’s also a bit, well, sticky. And that is the layer where the worms have entered the organic matter into the soil. They chew it up and they mix it with the soil. And that’s what you see. You can see a real big difference. And over here. Yeah. It’s still there. There’s a worm that is now asleep more or less. It’s hibernating because well, circumstances were good.

TWILLEY: Wieger’s worms are so happy they’re not just sleeping, they’re screwing.

WAMELINK: Bit to our surprise as well. But well, if you put four worms in a pot and afterwards there are six and you have two really small ones then you know that something has happened there.

GRABER: So things sound great. The worms are happy, the plants are happy, is it time for us all to pick up and move to lava tubes on Mars?

TWILLEY: Damn that sounds tempting. But there are a few more issues to solve.

WAMELINK: One of the other problems, especially on Mars, is that there is a poisonous compound in the soil that is called perchlorate.

GRABER: There’s no perchlorate in the soils that Wieger is using, because perchlorate is super toxic. Wieger thinks we’ll be able to solve that problem using bacteria that eat the perchlorate, but right now it’s just a theory.

TWILLEY: Also, minor issue: pollination. We’re sadly rapidly approaching the point where there are no pollinators left on earth but there are definitely none in space.

WAMELINK: But what we did was take a paintbrush and pollinate all the flowers ourselves. It’s quite a lot of work. You can’t do that on Mars or on the moon. That’s too laborious.

GRABER: Tiny little robot drone pollinators might sound like a solution, but Wieger says they probably wouldn’t work because a lot of flowers are specifically adapted to bees.

TWILLEY: Greenhouses in the Netherlands already use bumblebees, so we know they’re cool being indoors. And handily, bumblebees hibernate for six months, so they can just sleep on the long boring journey to Mars.

GRABER: But wait, there’s more.

TWILLEY: “But wait there’s more” is basically the story of space farming. So many challenges.

GRABER: There’s a lot to watch over and take care of on a space colony. And so while robots might not work as pollinators, they’re probably going to be important as farmers.

MASSA: Tending a few plants is one thing, but, you know, if you have an astronaut who has to take care of 200 plants, that’s a tremendous amount of time. And you know one of my colleagues said well we’re not sending people to Mars to be subsistence farmers.

TWILLEY: Or full-time handymen. Because that’s the other thing about all of these groovy space farming systems—they break. They’re so highly engineered to move gases around and catch and circulate water and keep the temperature and pressure stable and deliver specific light recipes—it’s a nightmare of moving parts.

GRABER: Ray Wheeler at NASA learned this at the very beginning of his career at the Biomass Production Chamber. This was one of the very first plant chambers that NASA ever built, back in the 1970s.

WHEELER: When we had failures, something went wrong. Invariably, it was an engineered component. a pump failed. The lights went out. The chiller stopped. You know those kinds of things. The biology was very predictable. It came in on the mark. The plants behave the way you would almost expect them.

TWILLEY: Once again, the plants are fine, the human side, not so much.

GRABER: So there are a lot of issues we still have to solve before we can set up a growing system that will sustain us on the moon or on Mars. But in the meanwhile, all this research is useful for farmers here on Earth, too.

TWILLEY: All of Wieger’s work on soil fertility and Esther’s research into light recipes, they’re helping farmers in The Netherlands—and ultimately elsewhere—figure out how to keep producing such high yields while reducing their energy and chemical inputs.

GRABER: Some people have gone as far as claiming that indoor, closed-loop greenhouses—like Eden ISS—these are going to solve all our food needs here on Earth, too. But these systems are still energy intensive and expensive. Esther has a colleague, Luuk Graamans. Luuk says where these space-like systems currently make more sense is for really high value crops.

TWILLEY: Like pharmaceutical plants. Or pot.

GRAAMANS: If you can start controlling all of these different aspects as opposed to some of them you can guide these plants much more specifically. And that can lead to a purer crop which you can then sell at a higher price, or you can have more nutrients in a crop etc. So those are really the spin offs that we’re currently seeing for Earth.

TWILLEY: So space agriculture has already brought us better pot. And frankly, I think Wieger could fund a space colony or two by growing grapes in his soil simulant and selling it as Martian wine. But no, he’s more interested in using what he’s learned to green the desert here on Earth. Go figure.

WAMELINK: Because well in the end these soils they come from desert or desert like situations where nothing or almost nothing grows. And what we’re basically doing is trying to find out how you can grow crops on them.

GRABER: He’s already done an experiment with desert sites in the Middle East. The results aren’t in yet, but Wieger is really excited.

TWILLEY: Obviously I am very happy to hear all of Wieger and Esther and Ray and Gioia’s work is useful here on earth. But what about actually growing food in space? Are we any closer to eating food that wasn’t grown on Earth?

GRABER: As it happens, this isn’t all theoretical! Scientists have grown plants on spaceships for a few decades, just for research.

TWILLEY: A lot of mustard plant relatives. To study. Not to eat.

GRABER: But there are real crops on the international space station. The latest space farming experiment going on on the ISS is a NASA project called Veggie.

MASSA: Veggie is a small plant growth chamber for the international space station. It’s probably, hm, about the size of a microwave oven, but kind of up on end.

TWILLEY: The first plant grown in one of these Veggie systems was…. Drum roll… A red romaine lettuce, called Outredgeous. In 2014.

GRABER: Yum. But actually the astronauts who first harvested outredgeous weren’t allowed to taste it. Those first plants were sent back to Earth to make sure they were safe to eat.

MASSA: We have heard that a leaf may not have made it back to Earth, but we did get all the plant samples back that you know we expected at least, it was kind of hard to count leaves when it’s all frozen.

TWILLEY: The official tasting came later. Basically there was a giant truckload of institutional bureaucracy to go through before the U.S. astronauts were given permission to eat one of these lettuce leaves. But eventually the day arrived, and astronauts Scott Kelly, Kimiya Yui, and Kjell Lindgren enjoyed a leaf each on camera.

ASTRONAUT TAPE

ASTRONAUTS: Woohoo! Cheers! LAUGHTER
GRABER: It wasn’t a lot of greens, just a few lettuce leaves, not even enough for a salad. But the astronauts, as you can tell, they were pretty excited to try space crops. And so were we.

WAMELINK: I’ve got three here in my window aisle. There’s a garden cress in it. And there’s one with moon soil, there’s one with Martian soil. And there’s one with Earth control. And well you can see they are green. You can eat them if you want to. Yeah. Yes, you can try if you want to.

TWILLEY: Yes, we were in The Netherlands not in space. But hot damn, it’s not everyday you get to try cress grown in Martian and lunar soil! We were pretty excited.

WAMELINK: And well, just take a leaf and try one.

GRABER: Okay.

WAMELINK: Tell me, I will take one as well.

GRABER: So the Martian first.

TWILLEY: Martian first yeah, I think. Yeah.

GRABER: Okay.

WAMELINK: Oh yeah. This one is very spicy.

GRABER: Mm, that’s delicious.

GRABER: Wieger held a dinner for some of the people who helped fund this experiment. Those folks were the first commoners who got to try his Martian and lunar plants. And they thought that the veggies tasted different, depending on which soil they were grown in.

TWILLEY: Overall the verdict was that Moon tomatoes and Moon cress were spicier and Mars veggies were slightly sweeter.

GRABER: But that might have just been the power of suggestion. Wieger had the plants chemically analyzed, and he couldn’t find any detectable difference in the nutrients or flavor compounds.

TWILLEY: But whatever. I tasted the difference.

GRABER: I want to try the Mars one again.

TWILLEY: Mars is my favorite. It’s really nice and sweet.

WAMELINK: Yeah well it’s also my favorite. As you know.

TWILLEY: I know. You have influenced me, clearly.

GRABER: So the Mars one looked smaller to me, the leaves. So when I took two of them, I’m getting the same horseradish hit. I’m doing my own little controlled experiment here.

TWILLEY: Your data, Cynthia, are surely very scientific.

WAMELINK: They’re all spicy.

TWILLEY: Once we were done snarfing Martian cress, I noticed that Wieger had a one way ticket to Mars framed on his wall. He told us it was a gift from his colleagues.

GRABER: Wieger really does believe that we will be going to Mars, some day.

WAMELINK: I think it’s, yes, it’s going to happen. And I don’t think that we will go before 2030. Whatever Elon Musk says. But it will be after that. Soon after that, I think we will go to Mars. But it’s still then a long way from that first voyage going—maybe not even going down to the surface. But well, let’s say the first step on Mars. Then it’s still going to be a long way to that we have a settlement there and that we’re going to grow our crops.

TWILLEY: So on that timeline, maybe by 2050 we’ll start farming on Mars? Maybe we’ll be able to solve all the challenges we still face by then? Wieger’s optimistic.

GRABER: But even if we do solve all those challenges, Wieger’s not actually planning to use his ticket.

WAMELINK: I’m not going. You may be a bit disappointed by this answer but I would go to the moon if they invited me to set up a system like this to grow crops. But half a year at least in a spaceship?

CLIP: Houston we have a problem.

MUSIC UP

TWILLEY: Thanks this episode to Wieger Wamelink, Esther Meinen, and Luuk Graamans, all at Wageningen University in the Netherlands, as well as Gioia Massa and Ray Wheeler at NASA’s Kennedy Space Center.

GRABER: Thanks as well to our fabulous intern Emily Pontecorvo, who helped produce this episode. And to you enthusiastic listeners who piped up on Twitter and Facebook with your thoughts about examples of space farming in TV and movies. Turns out there aren’t actually a lot of great audio examples of space farming in pop culture, but we had fun watching movies and episodes that you suggested!

TWILLEY: Thanks to journalist Peter Smith who helped us with some algae info. And thanks also to the Alfred P. Sloan Foundation for the Public Understanding of Science, Technology, and Economics for their support of this episode.

POST-ROLL