The world’s next big environmental problem could come from space

Early on a Sunday morning in September, a team of 12 sleep-deprived, jet-lagged researchers assembled at the world’s most remote airport. There, on Easter Island, some 2,330 miles off the coast of Chile, they were preparing for a unique chase: a race to catch a satellite’s last moments as it fell out of space and blazed into ash across the sky.

That spacecraft was Salsa, one of four satellites that were part of the European Space Agency (ESA) Cluster constellation. Salsa and its counterparts had been studying Earth’s magnetic field since the early 2000s, but its mission was now over. Months earlier, the spacecraft had been set on a spiral of death that would end with a fiery disintegration high up in Earth’s atmosphere about a thousand miles away from Easter Island’s coast.

Now, the scientists were poised to catch this reentry as it happened. Equipped with precise trajectory calculations from ESA’s ground control, the researchers took off in a rented business jet, with 25 cameras and spectrometers mounted by the windows. The hope was that they’d be able to gather priceless insights into the physical and chemical processes that occur when satellites burn up as they fall to Earth at the end of their missions.

Researchers were able to monitor the reentry of Cluster Salsa from a rented business jet.

This kind of study is growing more urgent. Some 15 years ago, barely a thousand satellites orbited our planet. Now the number has risen to about 10,000, and with the rise of satellite constellations like Starlink, another tenfold increase is forecast by the end of this decade. Letting these satellites burn up in the atmosphere at the end of their lives helps keep the quantity of space junk to a minimum. But doing so deposits satellite ash in the middle layers of Earth’s atmosphere. This metallic ash can harm the atmosphere and potentially alter the climate. Scientists don’t yet know how serious the problem is likely to be in the coming decades.

The ash from the reentries contains ozone-damaging substances. Modeling studies have shown that some of its components can also cool down Earth’s stratosphere, while others can warm it. Some worry that the metallic particles could even disrupt Earth’s magnetic field, obscure the view of Earth-observing satellites, and increase the frequency of thunderstorms.

“We need to see what kind of physics takes place up there,” says Stijn Lemmens, a senior analyst at ESA who oversaw the campaign. “If there are more [reentering] objects, there will be more consequences.”

A community of atmospheric scientists scattered all over the world is awaiting results from these measurements, hoping to fill major gaps in their understanding. 

The Salsa reentry was only the fifth such observation campaign in the history of spaceflight. The previous campaigns, however, tracked much larger objects, like a 19-ton upper stage from an Ariane 5 rocket.  

Cluster Salsa, at 550 kilograms, was quite tiny in comparison. And that makes it of special interest to scientists, because it’s spacecraft of this general size that will be increasingly crowding Earth orbit in the coming years.

The downside of mega-constellations

Most of the forecasted growth in satellite numbers is expected to come from satellites roughly the same size as Salsa: individual members of mega-constellations, designed to provide internet service with decent speed and latency to anyone, anywhere.

SpaceX’s Starlink is the biggest of these. Currently consisting of about 6,500 satellites, the fleet is expected to mushroom to more than 40,000 at some point in the 2030s. Other mega-constellations, including Amazon Kuiper, France-based E-Space, and the Chinese projects G60 and Guowang, are in the works. Each could encompass several thousand satellites, or even tens of thousands. 

Mega-constellation developers don’t want their spacecraft to fly for two or three decades like their old-school, government-funded counterparts. They want to replace these orbiting internet routers with newer, better tech every five years, sending the old ones back into the atmosphere to burn up. The rockets needed to launch all those satellites emit their own cocktail of contaminants (and their upper stages also end their life burning up in the atmosphere).

The amount of space debris vaporizing in Earth’s atmosphere has more than doubled in the past few years, says Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who has built a second career as a leading space debris tracker..

“We used to see about 50 to 100 rocket stages reentering every year,” he says. “Now we’re looking at 300 a year.” 

In 2019, some 115 satellites burned up in the atmosphere. As of late November, 2024 had already set a new record with 950 satellite reentries, McDowell says.

The mass of vaporizing space junk will continue to grow in line with the size of the satellite fleets. By 2033, it could reach 4,000 tons per year, according to estimates presented at a workshop called Protecting Earth and Outer Space from the Disposal of Spacecraft and Debris, held in September at the University of Southampton in the UK.

Crucially, most of the ash these reentries produce will remain suspended in the thin midatmospheric air for decades, perhaps centuries. But acquiring precise data about satellite burn-up is nearly impossible, because it takes place in territory that is too high for meteorological balloons to measure and too low for sounding instruments aboard orbiting satellites. The closest scientists can get is remote sensing of a satellite’s final moments.

Changing chemistry

None of the researchers aboard the business jet turned scientific laboratory that took off from Easter Island in September got to see the moment when Cluster Salsa burst into a fireball above the deep, dark waters of the Pacific Ocean. Against the bright daylight, the fleeting explosion appeared about as vivid as a midday full moon. The windows of the plane, however, were covered with dark fabric (to prevent light reflected from inside to skew the measurements), allowing only the camera lenses to peek out, says Jiří Šilha, CEO of Slovakia-based Astros Solutions, a space situational awareness company developing new techniques for space debris monitoring, which coordinated the observation campaign.

“We were about 300 kilometers [186 miles] away when it happened, far enough to avoid being hit by any remaining debris,” Šilha says. “It’s all very quick. The object reenters at a very high velocity, some 11 kilometers [seven miles] per second, and disintegrates 80 to 60 kilometers above Earth.”

ESA

The instruments collected measurements of the disintegration in the visible and near-infrared part of the light spectrum, including observations with special filters for detecting chemical elements including aluminum, titanium, and sodium. The data will help scientists reconstruct the satellite breakup process, working out the altitudes at which the incineration takes place, the temperatures at which it occurs, and the nature and quantity of the chemical compounds it releases.

The dusty leftovers of Cluster Salsa have by now begun their leisurely drift through the mesosphere and stratosphere—the atmospheric layers stretching at altitudes from 31 to 53 miles and 12 to 31 miles, respectively. Throughout their decades-long descent, these ash particles will interact with atmospheric gases, causing mischief, says Connor Barker, a researcher in atmospheric chemical modeling at University College London and author of a satellite air pollution inventory published in early October in the journal Scientific Data. 

Satellite bodies and rocket stages are mostly made of aluminum, which burns into aluminum oxide, or alumina—a white, powdery substance known to contribute to ozone depletion. Alumina also reflects sunlight, which means it could alter the temperature of those higher atmospheric layers.

“In our simulations, we start to see a warming over time of the upper layers of the atmosphere that has several knock-on effects for atmospheric composition,” Barker says. 

For example, some models suggest the warming could add moisture to the stratosphere. This could deplete the ozone layer and could cause further warming, which in turn would cause additional ozone depletion.

The extreme speeds of reentering satellites also produces “a shockwave that compresses nitrogen in the atmosphere and makes it react with oxygen, producing nitrogen oxides,” says McDowell. Nitrogen oxides, too, damage atmospheric ozone. Currently, 50% of the ozone depletion caused by satellite burn-ups and rocket launches comes from the effects of nitrogen oxides. The soot that rockets produce alters the atmosphere’s thermal balance too.

In some ways, high-altitude atmospheric pollution is nothing new. Every year, about 18,000 tons of meteorites vaporize in the mesosphere. Even 10 years from now, if all planned mega-constellations get developed, the quantity of natural space rock burning up during its fall to Earth will exceed the amount of incinerated space junk by a factor of five.

That, however, is no comfort to researchers like McDowell and Barker. Meteorites contain only trace amounts of aluminum, and their atmospheric disintegration is faster, meaning they produce less nitrogen oxide, says Barker. 

“The amount of nitrogen oxides we’re getting [from satellite reentries and rocket launches] is already at the lower end of our yearly estimates of what the natural emissions of nitrogen oxides [from meteorites] are,” said Barker. “It’s certainly a concern, because we might soon be doing more to the atmosphere than naturally occurs.”

The annual amount of alumina from satellite reentries is also already approaching that arising from incinerated meteorites. Under current worse-case scenarios, the human-made contribution of this pollutant will be 10 times the amount from natural sources by 2040.

Impact on Earth?

What exactly does all this mean for life on Earth? At this stage, nobody’s certain. Studies focusing on various components of the air pollution cocktail from satellite and rocket activity are trickling in at a steady rate. 

Barker says computer modeling puts the current contribution of the space industry to overall ozone depletion at a minuscule 0.1%. But how much this share will grow 10, 20, or 50 years from now, nobody knows. There are way too many uncertainties in this equation, including the size of the particles—which will affect how long they will take to sink—and the ratio of particles to gaseous by-products.

“We have to make a decision, as a society, whether we prioritize reducing space traffic or reducing emissions,” Barker says. “A lot of these increased reentry rates are because the global community is doing a really good job of cleaning up low-Earth-orbit space debris. But we really need to understand the environmental impact of those emissions so we can decide what is the best way for humanity to deal with all these objects in space.”

FRAUNHOFER FHR

The disaster of 21st-century climate change was set in motion when humankind began burning fossil fuels in the mid-19th century. Similarly, it took 40 years for chlorofluorocarbons to eat a hole in Earth’s protective ozone layer. The contamination of Earth by so-called forever chemicals—per-and polyfluoroalkyl substances used in manufacturing nonstick coatings and firefighting foams—started in the 1950s. Researchers like McDowell are concerned the story may repeat yet again.

“Humanity’s activities in space have now gotten big enough that they are affecting the space environment in a similar way we have affected the oceans,” McDowell says. “The problem is that we’re making these changes without really understanding at what stage these changes will become concerning.”

Previous observation campaigns mostly analyzed the physical disintegration of reentering satellites. With the Cluster constellation, scientists hope to begin unraveling the chemical side of this elusive process. For researchers like Barker, that means finally getting data that could validate and further improve their models. The Cluster constellation will provide three more opportunities to fill the blanks in this environmental puzzle when the siblings of Salsa reenter in 2025 and 2026. 

“The great thing with Cluster is that we have four satellites that are identical and that we know every detail about,” says Šilha. “It’s a scientist’s dream, because we can repeat the experiment and learn from every previous campaign.”

The moon is just the beginning for this waterless concrete

If NASA establishes a permanent presence on the moon, its astronauts’ homes could be made of a new 3D-printable, waterless concrete. Someday, so might yours. By accelerating the curing process for more rapid construction, this sulfur-based compound could become just as applicable on our home terrain as it is on lunar soil. 

Artemis III—set to launch no earlier than September 2026—will not only mark humanity’s return to the moon after more than 50 years, but also be the first mission to explore the lunar South Pole, the proposed site of NASA’s base camp. 

Building a home base on the moon will demand a steep supply of moon-based infrastructure: launch pads, shelter, and radiation blockers. But shipping Earth-based concrete to the lunar surface bears a hefty price tag. Sending just 1 kilogram (2.2 pounds) of material to the moon costs roughly $1.2 million, says Ali Kazemian, a robotic construction researcher at Louisiana State University (LSU). Instead, NASA hopes to create new materials from lunar soil and eventually adapt the same techniques for building on Mars. 

Traditional concrete requires large amounts of water, a commodity that will be in short supply on the moon and critically important for life support or scientific research, according to the American Society of Civil Engineers. While prior NASA projects have tested compounds that could be used to make “lunarcrete,” they’re still working to craft the right waterless material.

So LSU researchers are refining the formula, developing a new cement based on sulfur, which they heat until it’s molten to bind material without the need for water. In recent work, the team mixed their waterless cement with simulated lunar and Martian soil to create a 3D-printable concrete, which they used to assemble walls and beams. “We need automated construction, and NASA thinks 3D printing is one of the few viable technologies for building lunar infrastructure,” says Kazemian. 

COURTESY OF ALI KAZEMIAN

Beyond circumventing the need for water, the cement can handle wider temperature extremes and cures faster than traditional methods. The group used a pre-made powder for their experiments, but on the moon and Mars, astronauts might extract sulfur from surface soil. 

To test whether the concrete can stand up to the moon’s harsh environment, the team placed its structures in a vacuum chamber for weeks, analyzing the material’s stability at different temperatures. Originally, researchers worried that cold conditions on the dark side of the moon might cause the compound to turn into a gas through a process called sublimation, like when dry ice skips its liquid phase and evaporates directly. Ultimately, they found that the concrete can handle the lunar South Pole’s frigid forecast without losing its form. 

Some conditions, like reduced gravity, could even work toward the concrete’s advantage. The experiment tested structures like walls and small circular towers, each made by stacking many layers of concrete. “One of the main challenges in larger-scale 3D printing is a distortion of these thick, heavy layers,” says Kazemian “But when you have lower gravity, that can actually help keep the layers from deforming.” 

Kazemian and his colleagues recently transferred the technology to NASA’s Marshall Space Flight Center in Huntsville, Alabama, to implement their design on a larger-scale robotic system and test construction in larger vacuum chambers. If adopted, the concrete will most likely be used for taller lunar structures like habitats and radiation shields. Flatter designs, like a landing pad, will probably use laser-based technologies to melt down lunar soil into a ceramic structure. 

There may only be so much testing we can do on Earth, however. According to Philip Metzger, a planetary physicist at University of Central Florida who recently retired from NASA’s Kennedy Space Center, the concrete’s efficacy may falter with the shift from simulant to real soil. “There’s chemistry in the samples of these planets that the simulants cannot perfectly replicate,” he says. “When we send missions to these planetary bodies to test the technology using the real soil, we may find that we need to further improve the technology to get it to work in that environment.”

But Metzger still sees the sulfur-based concrete as a vital foundation for the tall orders of upcoming planetary projects. Future missions to Mars could demand roads to drive back and forth from ice-mining sites and pavement around habitats to create dust-free work zones. This new concrete brings these distant goals a touch closer to reality. 

It could benefit construction on Earth, too. Kazemian sees the new material as a potential alternative for traditional concrete, especially in areas with water scarcity or a surplus of sulfur. Parts of the Middle East, for example, have abundant sulfur as a result of oil and gas production. 

The technology could become especially useful in disaster areas with broken supply chains, according to Metzger. It could also have military applications for rapid construction of structures like storage buildings. “This is great for people out there working on another planet who don’t have a lot of support,” Metzger says. “But there are already plenty of analogs to that here on Earth.”

Life-seeking, ice-melting robots could punch through Europa’s icy shell

At long last, NASA’s Europa Clipper mission is on its way. After overcoming financial and technological hurdles, the $5 billion mission launched on October 14 from Florida’s Kennedy Space Center. It is now en route to its target: Jupiter’s ice-covered moon Europa, whose frozen shell almost certainly conceals a warm saltwater ocean. When the spacecraft gets there, it will conduct dozens of close flybys in order to determine what that ocean is like and, crucially, where it might be hospitable to life.

Europa Clipper is still years away from its destination—it is not slated to reach the Jupiter system until 2030. But that hasn’t stopped engineers and scientists from working on what would come next if the results are promising: a mission capable of finding evidence of life itself.

This would likely have three parts: a lander, an autonomous ice-thawing robot, and some sort of self-navigating submersible. Indeed, several groups from multiple countries already have working prototypes of ice-diving robots and smart submersibles that they are set to test in Earth’s own frigid landscapes, from Alaska to Antarctica, in the next few years

But Earth’s oceans are pale simulacra of Europa’s extreme environment. To plumb the ocean of this Jovian moon, engineers must work out a way to get missions to survive a  never-ending rain of radiation that fries electronic circuits. They must also plow through an ice shell that’s at least twice as thick as Mount Everest is tall.

“There are a lot of hard problems that push up right against the limits of what’s possible,” says Richard Camilli, an expert on autonomous robotic systems at the Woods Hole Oceanographic Institution’s Deep Submergence Laboratory. But you’ve got to start somewhere, and Earth’s seas will be a vital testing ground. 

“We’re doing something nobody has done before,” says Sebastian Meckel, a researcher at the Center for Marine Environmental Sciences at the University of Bremen, Germany, who is helping to develop one such futuristic Europan submersible. If the field tests prove successful, the descendants of these aquatic explorers could very well be those that uncover the first evidence of extraterrestrial life.

Hellish descent

The hunt for signs of extraterrestrial biology has predominantly taken place on Mars, our dusty, diminutive planetary neighbor. Looking for life in an icy ocean world is a whole new kettle of (alien) fish, but exobiologists think it’s certainly worth the effort. On Mars, scientists hope to find microscopic evidence of past life on, or just under, its dry and frozen surface. But on Europa, which has a wealth of liquid water (kept warm by Jupiter, whose intense gravity generates plenty of internal friction and heat there), it is possible that microbial critters, and perhaps even more advanced small aquatic animals, may be present in the here and now.

The bad news is that Europa is one of the most hostile environments in the solar system—at least, for anything above its concealed ocean. 

When NASA’s Clipper mission arrives in 2030, it will be confronted by an endless storm of high-energy particles being whipped about by Jupiter’s immense and intense magnetic field, largely raining down onto Europa itself. “It’s enough to kill a regular person within a few seconds,” says Camilli. No human will be present on Europa, but that radiation is so extreme that it can frazzle most electronic circuits. This poses a major hazard for Europa Clipper, which is why it’s doing only quick flybys of the moon as its orbit around Jupiter periodically dips close.

Clipper has an impressive collection of remote sensing tools that will allow it to survey the ocean’s physical and chemical properties, even though it will never touch the moon itself. But almost all scientists expect that uncovering evidence of biological activity will require something to pierce through the ice shell and swim about in the ocean.

NASA/JPL-CALTECH

The good news is that any Europan life-hunting mission has a great technological legacy to build upon. Over the years, scientists have developed and deployed robotic subs that have uncovered a cornucopia of strange life and bizarre geology dwelling in the deep. These include remotely operated vehicles (ROVs), which are often tethered to a surface vessel and are piloted by a person atop the waves, and autonomous underwater vehicles (AUVs), which freely traverse the seas by themselves before reporting back to the surface.

Hopeful Europa explorers usually cite an AUV as their best option—something that a lander can drop off and let loose in those alien waters that will then return and share its data so it can be beamed back to Earth. “The whole idea is very exciting and cool,” says Bill Chadwick, a research professor at Oregon State University’s Hatfield Marine Science Center in Newport, Oregon. But on a technical level, he adds, “it seems incredibly daunting.”

Presuming that a life-finding robotic mission is sufficiently radiation-proof and can land and sit safely on Europa’s surface, it would then encounter the colossal obstacle that is Europa’s ice shell, estimated to be 10 to 15 miles thick. Something is going to have to drill or melt its way through all that before reaching the ocean, a process that will likely take several years. “And there’s no guarantee that the ice is going to be static as you’re going through,” says Camilli. Thanks to gravitational tugs from Jupiter, and the internal heat they generate, Europa is a geologically tumultuous world, with ice constantly fragmenting, convulsing and even erupting on its surface. “How do you deal with that?”

Europa’s lack of an atmosphere is also an issue. Say your robot does reach the ocean below all that ice. That’s great, but if the thawed tunnel isn’t sealed shut behind the robot, then the higher pressure of the oceanic depths will come up against a vacuum high above. “If you drill through and you don’t have some kind of pressure control, you can get the equivalent of a blowout, like an oil well,” says Camilli—and your robot could get rudely blasted into space.

Even if you manage to pass through that gauntlet, you must then make sure the diver maintains a link with the surface lander, and with Earth. “What would be worse than finally finding life somewhere else and not being able to tell anyone about it?” says Morgan Cable, a research scientist at NASA’s Jet Propulsion Laboratory (JPL).

Pioneering probes

What these divers will do when they breach Europa’s ocean almost doesn’t matter at this stage. The scientific analysis is currently secondary to the primary problem: Can robots actually get through that ice shell and survive the journey? 

A simple way to start is with a cryobot—a melt probe that can gradually thaw its way through the shell, pulled down by gravity. That’s the idea behind NASA’s Probe using Radioisotopes for Icy Moons Exploration, or PRIME. As the name suggests, this cryobot would use the heat from the radioactive decay of an element like plutonium-238 to melt ice. If you know the thickness of the ice shell, you know exactly how many tablespoons of radioactive matter to bring aboard. 

Once it gets through the ice, the cryobot could unfurl a suite of scientific investigation tools, or perhaps deploy an independent submersible that could work in tandem with the cryobot—all while making sure none of that radioactive matter contaminates the ocean. NASA’s Sensing with Independent Micro-Swimmers project, for example, has sketched out plans to deploy a school of wedge-shaped robots—a fleet of sleuths that would work together to survey the depths before reporting back to base.

These concepts remain hypothetical. To get an idea of what’s technically possible, several teams are building and field-testing their own prototype ice divers. 

One of the furthest-along efforts is the Ocean Worlds Reconnaissance and Characterization of Astrobiological Analogs project, or ORCAA, led by JPL. After some preliminary fieldwork, the group is now ready for prime time; next year, a team will set up camp on Alaska’s expansive Juneau Icefield and deploy an eight-foot tall, two-inch wide cryobot. Its goal will be to get through 1,000 feet of ice, through a glasslike upper layer, down into ancient ices, and ultimately into a subglacial lake.

NASA/JPL-CALTECH

This cryobot won’t be powered by radioactive matter. “I don’t see NASA and the Department of Energy being game for that yet,” says Samuel Howell, an ocean worlds scientist at JPL and the ORCAA principal investigator. Instead, it will be electrically heated (with power delivered via a tether to the surface), and that heat will pump warm water out in front of the cryobot, melting the ice and allowing it to migrate downward.

The cryobot will be permanently tethered to the surface, using that link to communicate its rudimentary scientific data and return samples of water back to a team of scientists at base camp atop the ice. Those scientists will act as if they are an astrobiology suite of instruments similar to what might eventually be fitted on a cryobot sent to Europa. 

The 2025 field experiment “has all the pieces of a cryobot mission,” says Howell. “We’re just duct-taping them together and trying to see what breaks.”

Space scientists and marine engineers are also teaming up at Germany’s Center for Marine Environmental Sciences (MARUM) to forge their own underwater explorer. Under the auspices of the Technologies for Rapid Ice Penetration and Subglacial Lake Exploration project, or TRIPLE, they are developing an ice-thawing cryobot, an astrobiological laboratory suite, and an AUV designed to be used in Earth’s seas and Europa’s ocean.

Their cryobot is somewhat like the one ORCAA is using; it’s an electrically heated thawing machine tethered to the surface. But onboard MARUM’s “ice shuttle” will be a remarkably small AUV, just 20 inches long and four inches wide. The team plans to deploy both on the Antarctic ice shelf, near the Neumayer III station, in the spring of 2026. 

MARUM – CENTER FOR MARINE ENVIRONMENTAL SCIENCES, UNIVERSITY OF BREMEN.

From a surface station, the ice shuttle will thaw its way down through the ice shell, aiming to reach the bitingly cold water hundreds of feet below. Once it does so, a hatch will open and the tiny AUV will be dropped off to swim about (on a probably preprogrammed route), wirelessly communicating with the ice shuttle throughout. It will take a sample of the water, return to the ice shuttle, dock with it, and recharge its batteries. For the field test, the ice shuttle, which will have some rudimentary scientific tools, will return the water sample back to the surface for analysis; for the space mission itself, the idea is that an array of instruments onboard the shuttle will examine that water.

As with ORCAA, the scientific aspect of this is not paramount. “What we’re focusing on now is form and function,” says project member Ralf Bachmayer, a marine robotics researcher at MARUM. Can their prototype Europan explorer get down to the hidden waters, deploy a scout, and return to base intact?

Bachmayer can’t wait to find out. “For engineers, it’s a dream come true to work on this project,” he says.

Swarms and serpents

A submersible-like AUV isn’t the only way scientists are thinking of investigating icy oceanic moons. JPL’s Exobiology Extant Life Surveyor, or EELS, involves a working, wriggling, serpentine robot inspired by the desire to crawl through the vents of Saturn’s own water-laden moon, Enceladus. The robotic snake has already been field-tested; it recently navigated through the icy crevasses and moulins of the Athabasca Glacier in Alberta, Canada.

Although an AUV-like cryobot mission is likely to be the first explorer of an icy oceanic moon, “a crazy idea like a robotic snake could work,” says Cable, the science lead for EELS. She hopes the project is “opening the eyes of scientists and engineers alike to new possibilities when it comes to accessing the hard-to-reach, and often most scientifically compelling, places of planetary environments.”

It might be that we’ll need such creative, and perhaps unexpected, designs to find our way to Europa’s ocean. Space agencies exploring the solar system have achieved remarkable things, but “NASA has never flown an aqueous instrument before,” says Howell.

But one day, thanks to this work, it might—and, just maybe, one of them will find life blooming in Europa’s watery shadows.

Robin George Andrews is an award-winning science journalist and doctor of volcanoes based in London. He regularly writes about the Earth, space, and planetary sciences, and is the author of two critically acclaimed books: Super Volcanoes (2021) and How To Kill An Asteroid (October 2024).

The quest to figure out farming on Mars

Once upon a time, water flowed across the surface of Mars. Waves lapped against shorelines, strong winds gusted and howled, and driving rain fell from thick, cloudy skies. It wasn’t really so different from our own planet 4 billion years ago, except for one crucial detail—its size. Mars is about half the diameter of Earth, and that’s where things went wrong.

The Martian core cooled quickly, soon leaving the planet without a magnetic field. This, in turn, left it vulnerable to the solar wind, which swept away much of its atmosphere. Without a critical shield from the sun’s ultraviolet rays, Mars could not retain its heat. Some of the oceans evaporated, and the subsurface absorbed the rest, with only a bit of water left behind and frozen at its poles. Unrelenting radiation, along with electrostatic discharge from planet-wide dust storms, drove chemical reactions in the arid Martian dirt, ultimately leaving it rich in pesky toxic salts called perchlorates. If ever a blade of grass grew on Mars, those days are over. 

But could they begin again? What would it take to grow plants to feed future astronauts on Mars? In science fiction, it isn’t much of a problem. Matt Damon’s character in the 2015 movie The Martian simply had to build a greenhouse, spread out human excrement, add water, and wait. The film got a lot of things right—bacteria in the human biome will be useful—but it didn’t account for the perchlorates. The potato plants that sustained him would never have grown, but even if they had, two years of eating contaminated, carcinogenic potatoes would have nuked his thyroid, boxed his kidneys, and damaged his cells—though he might not have realized it, because perchlorates are also neurotoxic. It would have been Matt Damon’s finest death scene.

At the time Andy Weir was writing the book on which the film was based, no one really knew just how plentiful and ubiquitous the chemicals were. Though they were first discovered by NASA’s Phoenix lander in 2008, it took subsequent rovers, and compilation of historic data, to confirm that not only are perchlorates everywhere on Mars, but they are, in fact, abundant. Overall, Mars’s surface has perchlorate concentrations of about 0.5% by weight. On Earth, the concentration is often a millionth that amount.

For NASA, that’s a devastating issue. The ultimate goal of the agency’s Artemis program is to land astronauts on Mars. And for the last decade, the agency has pursued a long-term plan of establishing an “Earth independent” human presence on the Red Planet. More ambitiously, if less plausibly, Elon Musk, the chief executive officer of SpaceX, has stated that he expects a million people to live on Mars in the next 20 years.

Any notion of an independent Mars means the perchlorate problem must be solved, because humans have to eat. Resupply missions are, by definition, Earth dependent, and hydroponics are inadequate for feeding people in large numbers.

“We can sustain crews of 10, maybe 20, very comfortably with hydroponics, but it doesn’t scale much larger than that,” says Rafael Loureiro, an associate professor at Winston-Salem State University who specializes in plant stress physiology. Hydroponics systems must be built on Earth, and they require energy-inefficient pumps and constant monitoring for bacterial and fungal infections. “Once the system is infected, you lose your entire crop, because it’s a closed-loop system,” he says. “You have to discard everything and reset.”

The only real path forward, says Loureiro, is farming the land: “The perchlorate problem is something that we will inevitably have to deal with.” 

There is no soil on Mars. Just dusty, poisonous regolith—the mixture of loose rock, sand, and dust that makes up the planetary surface. On Earth, the regolith is replete with billions of years’ worth of broken-­down organic biomass—soil—that just doesn’t exist on Mars. To grow food there, we can’t just drop seeds in the ground and add water. We will need to create a layer of soil that can support life. And to do that, we first have to get rid of those toxic salts.   

There’s more than one way to remove perchlorates. You can burn them out; the compounds break down around 750 °F, but for that, you’ll likely need power sources like nuclear reactors, and a lot of ancillary equipment. You can literally wash the perchlorates from the regolith, but, Loureiro explains, “the amount of water that you need to do that is ungodly, and water is a limited resource as far as we know.” That process would likewise take a significant amount of energy. “That’s something that’s not feasible long term,” he tells me. The ideal solution is not something dependent on heavy machinery. Rather, it would rely on something small—microscopic, in fact. 

NASA and the National Science Foundation are funding research into how future astronauts on Mars might use microbial life not only to remove perchlorates from the planet’s dirt, but also to shape and enrich the regolith into arable soil. The work builds on years of effort to do the same thing in different places on Earth, and if successful, it will improve farming on two planets for the price of one.

“If we are able to grow plants in Martian regolith, we can do it anywhere on Earth.”

Rafael Loureiro, associate professor, Winston-Salem State University

It’s easy to dismiss the idea of Martian agriculture as a distant issue for a fictional future, but scientists must solve these sorts of problems before the rockets launch, not after humans are on their way. And as with much of NASA’s research, solving problems “up there” applies directly to life “down here.” Simply put, what we learn from Mars could find use here on Earth to turn infertile wastelands into rich agricultural zones. On Earth, natural perchlorate levels are highest in desert regions.  In other areas, high levels are usually due to industrial waste. The toxins harm Earthen plants as much as they would prospective Martian ones. Which means it’s not just NASA that is interested in remediation—even the US Department of Agriculture is paying for such research. 

“If I’m able to grow plants in a completely alien environment, the technology that I create to do that is one hundred [percent] transferrable to places here on Earth that are food insecure. To places that are extremely arid and unfit for agriculture. To places that have been affected by mining companies that have polluted the soil,” says Loureiro.

“If we are able to grow plants in Martian regolith, we can do it anywhere on Earth.”

Thinking small

The science laboratory at Arizona State University’s Biodesign Institute looks like a large version of every biology classroom in America: long black tables, myriad microscopes, racks of vials. When you look closer, though, you realize that the microscopes are a little fancier, and there are high-tech instruments like gas chromatographs and organic carbon analyzers in the mix.

Anca Delgado, a microbiologist, meets me at the entrance, where we don white lab coats and goggles. “We don’t plan to splatter you with anything today, but we want to be safe,” she says. 

Earth’s soil is wet and wiggly, teeming with life, and its mineral composition is highly diverse, thanks in part to tectonic action, microbial activity, and the rock cycle. But you can just look at Mars and tell something is way off: The core of the diminutive planet cooled before much of its iron had a chance to sink to its center. As a result, Martian regolith is packed with iron-rich minerals, which over time have oxidized. The planet’s exterior is literally rusted. Without water, it changes primarily via mechanical weathering, driven by wind and temperature; and without life, it is entirely inorganic.

Despite all this, Delgado, her graduate students, and colleagues across the country have found a possible path to solving the perchlorate problem and making Martian regolith arable. 

Perchlorates are salts made out of a negatively charged ion of chlorine and oxygen, bonded with a positive ion such as sodium. (There is also perchloric acid, which contains that same negatively charged ion.)Where perchlorates are abundant on Earth, it is often because we put them there. Everything from military manufacturing to the fireworks spectacular at Disneyland has contributed. They weren’t the only chlorinated compounds the US went wild about around the time of World War II. The United States for decades made heavy use of organic chlorinated solvents in everything from dry cleaning and metal degreasing to clothing dyes and medicine. 

MEREDITH MIOTKE | PHOTO: NASA/JPL-CALTECH/MSSS

Industry overall had a laissez-­faire attitude toward the management of waste products, leading to contamination of the nation’s groundwater. “After the Clean Water Act and later legislation in the 1970s prevented or banned the use of some of these chemicals, that’s when we discovered the extent of this contamination,” Delgado tells me. Some water pollution was obvious. The Cuyahoga River in Ohio routinely caught on fire. But other contamination remained hidden. Residents of Love Canal, a neighborhood in the city of Niagara Falls, New York, reported abnormally high rates of leukemia markers and birth defects before anyone recognized that the 20,000 tons of chemicals dumped into a canal in the 1940s might be responsible. 

It wasn’t enough to stop dumping toxic chemicals in waterways and landfills, however. Scientists had to find alternatives—Disney developed a fireworks launcher in 2004 that eliminated its perchlorate emissions, for example—and they also had to find ways to clean up the pollution that was already there. In the case of perchlorates, they can do so chemically. Rain and artificial irrigation can wash the compounds away, though this only transfers the problem to groundwater. Another strategy is to grow woody plants like willow and cottonwood in contaminated lands. These draw perchlorates from the ground and can then be harvested, removing them from the contamination cycle.

Another biological approach is to go small, using microorganisms to turn toxic chemicals into harmless ones. The poster child for this concept is a bacterium called Dehalococcoides mccartyi, which specifically feeds on organic chlorinated solvents and spits out dechlorinated ethene (a simple, nontoxic hydrocarbon) and harmless chloride ions, which are found naturally in the environment. Delgado studied D. mccartyi during her doctoral program. Her interests were strictly terrestrial. But the process, while highly effective, was not perfect. It took an incredibly long time to work in nature.

“We were looking at treatment times of months to decades,” Delgado tells me. Her research sought to culture D. mccartyi at much higher densities, which would translate to improved rates of action and faster treatment times for abandoned American waste sites. Her work has since been applied at multiple field sites in Arizona, New Jersey, and California.

Delgado walks me through the lab, which is arranged in an open plan. From the Biodesign Institute’s inception in 2004, she says, the idea was to bring researchers who would not normally interact into the same physical space. That means microbiologists working with wastewater samples, sludges, and soils are next door to scientists who do DNA origami. 

The leap from cleaning up Earth’s toxic waste dumps to making the Martian surface arable began in 2017, a month before Delgado started her new job at the university. She had read an article about Mars and idly looked into the chemical elements that had been detected so far on that planet. “I like microbes, and I wanted to see if Mars could fulfill their nutritional requirements,” she says. “I’m sort of a sci-fi geek.”

While attending a university retreat designed to get researchers talking about their work, she decided to “put it out there” that “I would be interested at some point to look at whether microorganisms would be able to grow in Martian conditions.” 

A paper she read in the journal Nature finally spurred her into action. Soil organic matter, which is necessary for growing plants, is itself made of decomposing plant and animal material. That would seem to preclude Martian agriculture from ever being achieved. But researchers had demonstrated for the first time that you can actually form soil organic matter with microorganisms alone—no decaying plants needed. The microbes themselves, and their tissues and excretions, could synthesize soil.  

Delgado realized that perchlorates could be the initial catalyst, the thing that microbes could thrive on and break down. Eventually the process could make the Martian regolith ready for planting. 

She applied for an Emerging Frontiers in Research and Innovation grant from the National Science Foundation to explore the idea. NASA recognized her proposal’s implications and co-funded the grant; the project received $1.9 million total in 2022. It was intended as a multiyear, multi-institution effort, with Delgado as principal investigator. The plan was that ASU, the lead institution, would explore using microbes to lower the concentration of perchlorates in Mars-like dirt. The University of Arizona in Tucson would investigate the soil organic matter formed by those microbes during their breakdown of the perchlorates, and the Florida Institute of Technology in Melbourne, Florida, would figure out how to grow the plants.

Testing the dirt

One problem with studying Martian regolith is that we simply don’t have any of it here on Earth. NASA’s entire campaign of Mars exploration for 50 years has been in service of characterizing the Red Planet as a possible site for life. The agency has long sought to get a pristine sample of regolith from Mars into a clean room on Earth for analysis. But so far it has failed to develop a credible mission to do so. In April, Bill Nelson, the administrator of NASA, essentially admitted defeat, asking outside research institutions and the private sector for proposals on how an affordable Mars sample return might be achieved.

In the meantime, scientists have to make do with simulated Martian dirt to study ways to diminish levels of perchlorates, including heat, radiation, and microbial methods.

Delgado’s lab at ASU includes an incubator and a confocal microscope inside a custom-built anaerobic chamber, for analyzing microorganisms that are sensitive to oxygen. At a research station lined with sealed glassware of various sizes, plus syringes, pipettes, and other equipment, she introduces me to two of her doctoral students: Alba Medina, who is studying environmental engineering, and Briana Paiz, who studies biological design. Both are lead researchers on the project.

In sealed bottles on the table are solutions of various colors ranging from tan to black. In the more transparent solutions, a red material sits at the bottom that looks suspiciously similar in color to the dirt on Mars. “These are called microcosm bottles,” Delgado says. “To maintain the integrity of the chemicals and composition, anything that needs to be put in or taken out of the bottles has to be done by syringe and needle.”

The bottles contain nutrients, water (a requirement for life), and artificial Mars dirt. With no Martian regolith available, Delgado uses an “analogue” called MGS-1—Mars Global Simulant—with chemical and mineral composition, proportions, and physical properties engineered to match up with the specs measured by the Mars rover Curiosity. The simulant is made by a company called Space Resource Technologies and is publicly available. You can buy it online.

“It’s the most expensive dirt you’ll ever buy,” Delgado says with a laugh. After handing me a latex glove so I don’t get my hands dirty, she offers me a bag. It feels like the sort of sand you’d expect to find at beaches too expensive to visit. It is very fine; it looks and feels like cocoa powder.

All researchers have to add to the microcosm bottles are perchlorates, which come as a white powder. With that, they have Mars in a jar. 

“Then,” says Paiz, “we add the microbes.” She shows me around the various experiments. “Those microcosm bottles have Dechloromonas, and the ones in the back are actually pure cultures of Haloferax denitrificans”—a bacterium that thrives in salty environments. The team is also experimenting with myriad microbes in mixed communities, each interacting with different elements and compounds, yielding different chemical compositions in their respective microcosms. It’s why some bottles are the color of chocolate and others are the color of peanut butter.

“They all started off the same color,” says Medina. “The black color of this one is like a visual signature confirmation of activity by sulfate-reducing microorganisms, for example.” 

Bacteria eat the things they like and ignore the things they don’t. Delgado’s group is looking for the ideal combinations not only to eliminate perchlorates, but to do so efficiently. Perchlorates present opportunities as well. When Delgado’s microbes break those compounds down, they form chloride and oxygen. 

Astronauts could potentially use them to produce a “major source of oxygen on Mars,” says Delgado. “Maybe the biggest source. One of the things we have been thinking about is how we could capture it.”

Microbial cultures and strains need not be brought to Mars in giant vats. Microorganisms grow exponentially fast. With less than a gram of material—not even the weight of a paper clip—a scientist on Mars could propagate it infinitely. A few drops in a test tube could theoretically yield entire orchards.

But the ideal microbial transport systems are astronauts themselves. Our bodies already contain perchlorate-eating microbes in our gut biomes. Delgado’s group does its perchlorate research using microbial communities from sludge acquired from wastewater plants. So Matt Damon’s character in The Martian was, to an extent, on the right track. 

But even if the proper microbes for breaking down perchlorates are present, that does not mean they will be able to do their job. “Those communities already have perchlorate reducers, but they also come in with friends and enemies,” says Delgado. The thousands of strains of bacteria in our microbiomes compete for nutrients, making them inefficient. The trick is to find ways to help microbes that eat the bad stuff and reduce the population of microbes that get in the way. 

For now, regolith in very small batches is prepped at her lab. Successful perchlorate reduction brings the concentration from about five grams per kilogram (the original 0.5%) to five to 20 micrograms per kilogram—or less. Existing literature suggests that this concentration range does not inhibit seed germination. For comparison, soils in the Arizona desert have a background concentration of perchlorate ranging from 0.3 to five micrograms per kilogram. In the Atacama Desert, that figure can be up to 2,500 micrograms per kilogram. 

But removing perchlorates is not enough for Martian plants to thrive. “Once you get perchlorates out, you’re still left with the issue of how to convert Mars regolith to soil,” says Andrew Palmer, an associate professor of biology at the Florida Institute of Technology and a co-­investigator on Delgado’s project. 

MEREDITH MIOTKE | PHOTO: NASA/JPL-CALTECH/MSSS

Palmer explains that regolith, with or without perchlorates, is an inert substrate. Soil, strictly speaking, is a substrate that has been acted on by biology and acts on it in turn. But in the regolith simulant—and one day, perhaps, in actual Martian regolith—the microbial activity responsible for eliminating perchlorates might also be able to transform minerals and release other useful plant nutrients like potassium and phosphorus. Finding the best way to do this is one of the Delgado team’s goals in studying different microbial strains and sludge.

“The biological process for removing perchlorates should not only get rid of them, but should also help us put other nutrients into the soil,” Palmer tells me. “We are trying to put an ecological cycle into the regolith.”

Early signs are promising, but it is a years-long endeavor. Researchers have reduced perchlorates in regolith samples. They have increased concentrations of organics in samples. They have changed the structure of regolith. They have grown plants in it. Their goal is to do all those things at once. “The whole grant, the whole process with everybody involved, is turning regolith with perchlorates into soil that is amenable to plant growth,” says Palmer, “and that’s very powerful.” 

If all goes well, the regolith simulant should have a total organic carbon concentration two to five times higher than it did at the outset, thanks to the organic residues formed by microbes. Ultimately, it should also have better water-­holding capacity as the organic carbons change the physical properties of the otherwise clay-like regolith, making it less dense and more beneficial for plants and their root systems.

Once the regolith is ready and the scientists satisfied, the simulated Mars material heads to Palmer’s laboratory in Florida to see what might grow.

Tomatoes and quinoa

Palmer admits he wasn’t particularly interested in the problem of growing plants on Mars when representatives from NASA first approached him seven years ago. The work seemed boring to him: “Plants grow in dirt—film at 11,” he joked.

The more they talked, however, and the more NASA scientists explained the challenges of working with Mars simulants and issues such as the perchlorate problem, the more his curiosity was piqued. How were we going to provide a sufficient food supply there, anyway? He and his researchers at Florida Tech’s Palmer Lab of Chemical Ecology and Astrobiology began growing plants, fungi, and bacteria in lunar and Martian regolith simulants, exploring how to remodel regolith into soil that is amenable to plant growth. 

“Mars is six to nine months away. If you lose a food source, you may not be able to survive the wait for a resupply mission.”

Andrew Palmer, associate professor of biology, the Florida Institute of Technology

In addition to incubators, they use a room they’ve dubbed “the red house,” which is a semi-controlled environment.

“It’s a giant room, all artificial lighting and artificial environmental controls, and the plants we grow in there have never seen the light of day, which is what we think the situation would be like off Earth,” he says. Anything grown on Mars, which lacks a meaningful atmosphere and is colder than Antarctica, would likewise be grown in enclosed, controlled environments with artificial lighting.

Plants are grown and regrown in Mars simulants so that Palmer and his team can get a sense for how the regolith evolves simply from the growth process over time. Currently the researchers are growing romaine lettuce, bell peppers, tomatoes, and clover “pretty regularly” in commercially available Mars simulants. This semester, he says, they’ve also begun experimenting with peanuts and quinoa.

Because the project is still in its early stages, they do not have results to share related to the preliminary material they received from Arizona. On that, they are presently conducting germination assays. 

“We are still trying to understand how the simulant behaves physically, because when you add water, it can cake up—become really solid and dense—and that can stifle roots. It’s a really challenging problem,” he says.

One of the things they have found is that over time, growing plants in Mars simulant makes its texture “fluffier.” Palmer plans to use electron microscopy to study samples from Delgado’s lab. “Regolith grains are actually pretty jagged,” he tells me. This applies to both Martian and lunar regolith. “After things grow in it for a little while, usually bacteria will kind of make those particles more rounded.” This is because microorganism growth in regolith often results in the deposition of biofilms and other organic compounds, as well as etching or corrosion of grain surfaces. All this is beneficial for plant growth.

Palmer considers food security to be paramount for a mission to Mars, and the project’s research so far leaves him optimistic.

“Mars is six to nine months away. If you lose a food source, you may not be able to survive the wait for a resupply mission,” he says. The solution is diversity. There should be frozen food rations. Some things should be grown hydroponically. Some things should be grown in regolith. If one system fails, you still have the others to help you restart. It’s just good safety practice, he says, but more than that, if we are serious about making Mars a home, we must use the skills that make us special. Agriculture must surely be at the top of that list.

“There is something about cultivating a land that I think speaks to being a human,” Palmer says. “It means you have mastered that place. You only have control over a place when you have control over the soil.”

David W. Brown is a writer based in New Orleans. His next book, The Outside Cats, is about a team of polar explorers and his expeditions with them to Antarctica. It will be published in 2026 by Mariner Books.

NASA’s Europa Clipper spacecraft is set to look for life-friendly conditions around Jupiter

NASA is poised to launch Europa Clipper, a $5.2 billion mission to Jupiter’s fourth-largest moon, as early as October 10. The spacecraft will blast off from Kennedy Space Center in Florida atop a SpaceX Falcon Heavy rocket. It will study Europa, a possible home for extraterrestrial life, through a series of flybys after reaching Jupiter in 2030. 

Europa isn’t a craterous rock like our moon. Its surface is coated with ice, and telescope and spacecraft observations suggest it harbors a colossal liquid ocean in its interior that holds twice as much water as all of Earth’s oceans combined. Europa also possesses some of life’s critical building blocks: carbon, oxygen, hydrogen, nitrogen, phosphorus, and sulfur. These conditions could be sufficient for life to have developed there, either in the depths of the ocean or in subsurface lakes. 

Europa Clipper isn’t on the hunt for extraterrestrial life, however. Instead, its team hopes to assess the moon’s habitability—how well it could support life. The probe will use its range of scientific instruments, including cameras, spectrometers, magnetometers, and radars, to collect chemical, physical, and geological data in a series of flybys. Promising results could justify a mission to land on Europa and search for life. 

Early this year, everything seemed on track for the planned October launch. But in May, mission team members caught wind of a potential issue with Europa Clipper’s electronics. Testing data had indicated that the spacecraft’s transistors, devices that regulate the flow of electricity on the probe, wouldn’t survive the intense radiation consisting of charged particles trapped in Jupiter’s magnetic field, which is 20,000 times stronger than Earth’s. 

“The mission team was advised that similar parts were failing at lower radiation doses than expected,” NASA said in a statement. Disassembling the spacecraft and replacing faulty transistors could have pushed the mission’s launch window well past October. 

After months of follow-up testing at NASA’s Jet Propulsion Laboratory, Goddard Space Flight Center, and Applied Physics Laboratory, researchers concluded that any potential transistor damage wouldn’t impair mission operations. It was determined that the transistors could be heated to heal damage, and the 20-day breaks between large radiation exposures would offer enough recovery time. According to the New York Times, the spacecraft will also carry a box of the probe’s various transistors so that the team can monitor for damage, a bit like canaries in a coal mine. On September 9, Europa Clipper passed a milestone review called Key Decision Point E, approving it to proceed for launch. 

After arriving in orbit around Jupiter, Europa Clipper will conduct 49 close flybys of Europa. At its closest, the spacecraft will come within 16 miles (26 kilometers) of the surface for detailed observations. 

For more on Europa Clipper, see MIT Technology Review’s feature on the mission.

Job title of the future: Space debris engineer

Stijn Lemmens has a cleanup job like few others. A senior space debris mitigation analyst at the European Space Agency (ESA), Lemmens works on counteracting space pollution by collaborating with spacecraft designers and the wider industry to create missions less likely to clutter the orbital environment. 

Although significant attention has been devoted to launching spacecraft into space, the idea of what to do with their remains has been largely ignored. Many previous missions did not have an exit strategy. Instead of being pushed into orbits where they could reenter Earth’s atmosphere and burn up, satellites were simply left in orbit at the ends of their lives, creating debris that must be monitored and, if possible, maneuvered around to avoid a collision. “For the last 60 years, we’ve been using [space] as if it were an infinite resource,” Lemmens says. “But particularly in the last 10 years, it has become rather clear that this is not the case.” 

Engineering the ins and outs: Step one in reducing orbital clutter—or, colloquially, space trash—is designing spacecraft that safely leave space when their missions are complete. “I thought naïvely, as a student, ‘How hard can that be?’” says Lemmens. The answer turned out to be more complicated than he expected. 

At ESA, he works with scientists and engineers on specific missions to devise good approaches. Some incorporate propulsion that works reliably even decades after launch; others involve designing systems that can move spacecraft to keep them from colliding with other satellites and with space debris. They also work on plans to get the remains through the atmosphere without large risks to aviation and infrastructure.

Standardizing space: Earth’s atmosphere exerts a drag on satellites that will eventually pull them out of orbit. National and international guidelines recommend that satellites lower their altitude at the end of their operational lives so that they will reenter the atmosphere and make this possible. Previously the goal was for this to take 25 years at most; Lemmens and his peers now suggest five years or less, a time frame that would have to be taken into account from the start of mission planning and design. 

Explaining the need for this change in policy can feel a bit like preaching, Lemmens says, and it’s his least favorite part of the job. It’s a challenge, he says, to persuade people not to think of the vastness of space as “an infinite amount of orbits.” Without change, the amount of space debris may create a serious problem in the coming decades, cluttering orbits and increasing the number of collisions.  

Shaping the future: Lemmens says his wish is for his job to become unnecessary in the future, but with around 11,500 satellites and over 35,000 debris objects being tracked, and more launches planned, that seems unlikely to happen. 

Researchers are looking into more drastic changes to the way space missions are run. We might one day, for instance, be able to dismantle satellites and find ways to recycle their components in orbit. Such an approach isn’t likely to be used anytime soon, Lemmens says. But he is encouraged that more spacecraft designers are thinking about sustainability: “Ideally, this becomes the normal in the sense that this becomes a standard engineering practice that you just think of when you’re designing your spacecraft.”