‘Simulant’ Is the Boom Industry of the New Space Age

There has never been a better time to be in the market for some high-quality fake space dirt. As humans dream of new missions beyond our planet, the demand for simulants—materials designed to mimic alien surfaces, like those on Moon, Mars, and even unexplored worlds—is skyrocketing. 

These ersatz extraterrestrial soils have been around since the dawn of the space age, but a new rush of commercial, governmental, and scientific interest in interplanetary exploration is fueling a dazzling proliferation of recipes and options. Some of the most accurate simulants are extremely dangerous to handle, as off-Earth environments often contain hazardous chemicals and abrasive materials. For this reason, companies, nonprofits, and research institutions concoct different varieties of fake soil, tailored for use by everyone from rocket scientists to schoolchildren.

The boom in this multi-million dollar industry has been especially noticeable in recent years, as mission planners rev up to launch a host of next-generation space voyages, according to Parks Easter, the geotechnical quality manager at Exolith Lab, a nonprofit organization based at the University of Central Florida (UCF) campus in Orlando.

“As we started to make simulants and sent out orders, just more and more and more would come in,” Easter said in a call. Exolith Lab “used to be really small—just a warehouse with no air conditioning—and we would just go in and make a few kilograms of lunar or Martian simulant a week. Now, we have a team of around 35 or 40, making tons per week.” 

Who’s using all that fake space dirt, and for what? In classrooms across the country, students plant seeds in kid-friendly Mars simulant supplied by companies, such as Austin-based startup The Martian Garden. Space agencies fill giant sandboxes with the stuff to test-drive interplanetary rovers. There are simulants that imitate the exotic surfaces of asteroids, comets, or the moons of Mars. And there is always the lure of the “unicorn simulant,” a term coined by Melissa Roth and Vince Roux, the co-owners and lead researchers of Off Planet Research, a simulant company based in Everett, Washington, to describe space dirt with customizable properties such as grain size, composition, temperature, and even magnetic strength.

“We want to be that company that if you have a challenge, whether it's lunar or otherwise, that you can come to us and we can work together to find a solution,” said Roth in a call.

“We can make something that only exists on another planet,” added Roux in the same call. “It's just a lot of fun.”

The first extraterrestrial simulants were manufactured during the Apollo era, but curiosity about the properties of celestial bodies dates back into prehistory. For thousands of years, people speculated about the surface of the Moon, the closest alien world to Earth, suggesting that it might bear oceans, or gods, or even green cheese. But unraveling the mystery of the lunar landscape took on a new urgency in the 1960s, as humans prepared to set foot on another world for the first time. 

In anticipation of the Apollo missions, researchers developed rough lunar simulants, but it wasn’t until astronauts started hauling Moon rocks back to Earth that the mock soils took on any verisimilitude to real regolith, which is the rocky surface material—A.K.A., dirt—found on terrestrial worlds like Earth, the Moon, and Mars. 

Just as you might substitute an ingredient in a recipe, simulant makers hunt for materials on Earth that are analogous to those found in lunar environments, such as basalt, glass, and even ancient ice. No rocks have been returned from Mars yet—though NASA’s Perseverance rover is currently setting the stage for just such a sample return—but orbital and surface missions to the red planet since the 1970s, along with the occasional Martian meteorite, have helped inform the production of Martian simulants. Some simulants are also designed to mimic properties other than composition, depending on their intended use, such as mechanical behavior or structural likeness. 

For many decades, these simulants were largely developed in-house by NASA and other contracted research institutions. But a market for new varieties of simulants has emerged over the past decade due to a collision of several major space trends. 

NASA’s plans to spearhead a return to the Moon as part of its Artemis Program, a major project that requires simulants that mimic ultra-specific sites on the lunar surface. Many other space agencies around the world are also embarking on ambitious space missions that require exotic simulants; for instance, the Japan Aerospace Exploration Agency (JAXA) plans to return samples from Mars’ moon Phobos. Meanwhile, the maturation of the commercial space industry has boosted demand for simulants in experiments, including a field called in situ resource extraction (ISRU) which is dedicated to mining extraterrestrial surfaces for water, minerals, and other useful materials that could be used for life support, fuel, and even off-Earth infrastructure. 

Off Planet Research, which specializes in lunar simulants, was founded in 2015 to meet the demands of Moon-eyed companies and agencies. At that time, Roth recalled, simulants weren’t widely available outside of government or research facilities, so customers often resorted to buying generic materials second-hand, or even third-hand, from various suppliers.  

“We said: ‘Okay, if we're going to have a sustainable path back to the Moon as an industry, we also need that as a company,” she noted. “That was really important to us—to develop products that could help meet the very wide range of needs in this industry.”

To that point, simulant makers have become pros at developing realistic stand-ins for the finer details of the Moon’s surface, such as the presence of “agglutinates,” which are glassy materials that are created by tiny impacts that constantly pelt the lunar surface.  

“We call them the ‘Angry Cheerios of space,’' Roth said, noting that the company’s agglutinates mimic the mechanical properties of those found on the Moon. “They tend to be ring-shaped but they are also broken into parts. They're very high in glass content; they are created when little micrometeorites strike the surface and cause a bunch of small particles to fuse together, so they create very different properties when you incorporate them into a simulant.”

An increasing variety of educational and recreation simulants, designed for all skill levels and ages, are also available, but not all simulants are made for amateurs. Some of the products at Exolith Lab or Off Planet Research can be a little more hardcore, though both organizations can make customizable regoliths that can be safely handled by anyone.

“It's always important to understand who you're selling to,” said Roux. “Safety is something that is very important because if you mishandle some of the materials that we make, it can be bad.”

For instance, lunar regolith is notorious for its incredibly fine particles, which can be corrosive to robotic structures as well as a health hazard for humans. For this reason, Roth noted that some of Off Planet Research’s products should only be used with special ventilation systems and the kinds of personal protective equipment (PPE) that we have all become familiar with due to the COVID-19 pandemic.

“That is something that we're very aware of and like to discuss with all of our clients, but especially with those that, maybe, don't have prior simulant handling experience,” Roth noted.

This attention to safety is also a key concern for the team at Exolith Labs, which sports a catalog filled with interesting simulants designed to mimic sites like Jezero Crater, a dried-up lakebed on Mars that is now home to the Perseverance rover, or materials known as carbonaceous chondrites, which are found on ancient asteroids throughout the solar system. 

Founded in 2017 by Dan Britt, a UCF professor of astronomy and planetary sciences, Exolith Lab’s customers include federal space agencies such as NASA and JAXA, the commercial space sector, universities, and individual researchers. Easter said that the nonprofit is essentially game to try to make any kind of simulant, but emphasized that there are constraints and hazards inherent to the work. 

As examples, he cited nanophase iron, a highly refined substance that is produced in the unique environment on the Moon, as well as toxic chemicals called perchlorates, which are abundant on Mars and can be fatal to humans.

“There are definitely things that aren't able to be included in the simulant just because of earthly limitations,” Easter said, referring to nanophase iron. “We choose not to replicate certain things like perchlorates because they are really, really deadly to humans. If someone wants perchlorates, they can add it themselves after—it's not too difficult—but there are things that we choose to leave out.”

Many of these simulant products also require special packaging and shipping procedures. When the University of Adelaide ordered an astonishing 15 tons of lunar regolith for their rover test course, Exolith Lab met the challenge of both filling the order and shipping this immense amount of fake dirt across the world. The transaction required filling a shipping container with pallets stocked with bags of the nonprofit’s lunar highlands simulant LHS-1, which spent a month en route to the port of Adelaide. 

Meanwhile, Off Planet Research also faces transportation challenges with products such as its OPRFLCROSS2 simulant, which is designed to mimic the tantalizing lunar ice at the Moon’s south pole. Ancient ice in the region has been able to evade erosion by remaining ensconced in permanently shadowed craters, offering a potential resource to robotic or human crews that might land there. 

Named in part after the Lunar Crater Observation and Sensing Satellite (LCROSS), an experiment that blasted some of this ice into space in 2009, Off Planet Research’s icy simulant is especially compelling to mission planners that see this key region as a source of fuel, breathable oxygen, and drinkable water, among other applications. But because of the unusual landscape it simulates, the material must be kept at very cold temperatures using liquid nitrogen. 

Roth also noted that in addition to water, “there's lots of other fun chemicals involved, such as methane, hydrogen sulfide, ammonia, and carbon dioxide, which were also picked up in those signatures” created by LCROSS’s impact.

“It's important that [customers] are properly set up for the type of material they're getting,” she continued. “We can offer different variations of that ice that maybe don't include some of those gasses that are of more concern. But other researchers want those gasses included as part of the research they're doing and so being able to offer that variety and customization with our ice process as well is very important to us.” 

“It gets into some really interesting stuff,” Roux added of OPRFLCROSS2. “There are not a lot of organizations that can develop cryogenic simulants” which are “simulants that are made at cryogenic temperatures to replicate the properties of ice regolith on the Moon, and other worlds like Mars, comets, and asteroids.”

“I think that's the latest big jump,” he said.

Outside of these professional circles, hobbyists with all kinds of backgrounds have begun to dabble with simulant in experiments at home and in schools. Mark Cusimano, co-founder and CTO of The Martian Garden, is especially inspired by this application of simulants as a recreational and educational STEM (science, technology, engineering, and mathematics) tool that can help get anyone excited about space. 

Cusimano and his business partner, Steven Shields, initially came up with the idea for their company, which sells Martian simulant planting kits, while working as park rangers for the city of Austin, Texas. As part of that job, the pair developed a trailside astronomy program where they offered passers-by a chance to look at celestial objects like the Moon, Mars, or Saturn through a telescope—an invitation that Cusimano said most people were thrilled to take up.

“We were working with the public so much, we were both interested in space, and we were looking for something to branch out and do our own thing with,” Cusimano said in a call. “We wanted to create something that was an effective STEM engagement tool for classrooms because that's what was really rewarding to us about the trailside program—just getting to share that with people and seeing, especially with kids, how excited they got.”

Since its founding in 2016, The Martian Garden has become a popular resource for educators like Lori Nelson, who is a STEM teacher at Hampton Cove Elementary School in Alabama. Nelson, a self-described “huge space nerd,” designed a whole unit centered on growing plants in simulant supplied by The Martian Garden, as well as regular soil and a hydroponic system. That lesson plan has since won the Sylvia Shugrue Award for Elementary School Teachers, and been duplicated by many other teachers across the country.

“We did a whole lesson one day of just feeling the soil and describing the properties of the soil,” Nelson said in a call. “For elementary students, that's a huge component where it makes it real to them.” 

“It just brought it to a whole new level for them,” she added. “They really understand the challenges of space travel because they can see the soil, and how it looks different, it feels different, and the seeds don't grow the same way.”

Naturally, these experiments bring to mind Matt Damon’s efforts to grow potatoes on Mars in the 2015 film The Martian, based on the novel of the same name by Andy Weir. Cusimano said that this fictional depiction was definitely baked into the inspiration for his work; he has special fondness for the scenes of Damon singing to his extraterrestrial potato garden.

But while The Martian Garden is always open to orders from research specialists—perhaps even would-be Mars astronauts—the company is, at heart, built for people like Nelson, her students, and anyone who is interested in imagining life in extraterrestrial environments. To that end, the company’s simulant has even been used by Ed Guinan, a professor of astronomy and astrophysics at Villanova University, to brew Martian beer with his college students.

“We're weighing our options on creating new simulants, but our current focus is trying to expand our options for educators,”  Cusimano said. “That's always going to be our most important customer base, so we're looking to, perhaps, create a curriculum in the near future to go along with our materials so that teachers have something that's an all-inclusive solution for bringing this into the classroom.”

While the simulant market is dominated by lunar and Martian soils, many makers are also open to trying their hand at materials made to mimic worlds we have never visited, not even with robots. The Colorado School of Mines curates an ever-evolving database of these simulants, which is frequently updated with new recipes from the world of fake space soils.

For instance, JAXA began to search for a special simulant in advance of its Martian Moons eXploration mission, which aims to send a spacecraft to Mars’ moon Phobos in order to pick up a sample and return it to Earth, all within the next ten years. The project requires special simulant imitating the surface of Phobos, which Exolith Lab was able to design and manufacture.

“One of my favorite simulants is our Phobos stimulant,” Easter said. “We've also done that with a few other planets. I believe there's work on some Trojan asteroids simulant and there's a few different versions of Phobos. In general, if we're able to get a good estimate of the mineralogy of a body, we can pretty much make a custom for anyone, so we make it as the requests come in essentially.”

As new missions to explore other frontiers in the solar system get greenlit, even more challenging and unusual simulants will materialize in workshops and laboratories across the world. Perhaps the simulant database will one day include the hydrocarbon-rich materials that cover Saturn’s moon Titan, or the icy shell of Jupiter’s potentially habitable moon Europa, or the pressure-cooked detritus on the surface of Venus.

“I'm of the belief that when you're in such a tiny niche, a rising ocean lifts all ships,” said Cusimano. “I hope that there are more Mars simulants, I hope that we get lunar and Venusian simulants, and Titan and Pluto and everything else that we possibly can, because anything that helps people get excited about space, particularly when they are young, is going to translate into more public support for space exploration.”

“We need people to be excited about this so that the stakeholders will put more money towards it, so we can all get to this goal of being multi-planetary a lot sooner,” he concluded. “The more the merrier, as far as I'm concerned.”