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The Search for Intelligent Life Is About to Get a Lot More Interesting

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When the space shuttle Atlantis lifted off from the Kennedy Space Center on Oct. 18, 1989, it carried the Galileo in its cargo bay. Arrayed with scientific instruments, Galileo’s ultimate destination was Jupiter, where it would spend years in orbit collecting data and taking pictures. After it left the shuttle, though, Galileo headed in the other direction, turning toward the sun and circling around Venus, in order to slingshot around the planet and pick up speed for its journey to the outer solar system. Along the way, it flew around Earth too — twice, in fact, at altitudes of 597 and 188 miles. This gave its engineering team an opportunity to test the craft’s sensors. The astronomer Carl Sagan, a member of Galileo’s science team, called the maneuver the first flyby in our planet’s history. It also allowed him to contemplate what a spacecraft might find when looking at a far-off planet for signs of intelligent life.

There was plenty to see. Our technology creates an intriguing mess. Lights blaze, and heat islands glow in paved-over urban areas. Atmospheric gases ebb and flow — evident today not only in rising concentrations of carbon dioxide and methane, but also in clouds of floating industrial byproducts. Sometimes there are radiation leaks. And all the while, billions of gadgets and antennas cast off a buzzing, planetary swarm of electromagnetic transmissions.

Would other planets’ civilizations be like ours? Would they create the same telltale chemical and electromagnetic signs — what scientists have recently begun calling technosignatures — that Galileo detected? The search for intelligence beyond Earth has long been defined by an assumption that extraterrestrials would have developed radio technologies akin to what humans have created. In some early academic papers on the topic, dating to the late 1950s, scientists even posited that these extraterrestrials might be interested in chatting with us. “That played into this whole idea of aliens as salvation — you know, aliens were going to teach us things,” Adam Frank, an astrophysicist at the University of Rochester, told me recently. Frank points out that the search for signals from deep space has, over time, become more agnostic: Rather than looking for direct calls to Earth, telescopes now sweep the sky, searching billions of frequencies simultaneously, for electronic signals whose origins can’t be explained by celestial phenomena. At the same time, the search for intelligent life has turned in a novel direction.

In 2018, Frank attended a meeting in Houston whose focus was technosignatures. The goal was to get the 60 researchers in attendance to think about defining a new scientific field that, with NASA’s help, would seek out signs of technology on distant worlds, like atmospheric pollution, to take just one example. “That meeting in Houston was the dawn of the new era, at least as I saw it,” Frank recalls. NASA has a long history of staying out of the extraterrestrial business. “Everybody was sort of there with wide eyes — like, ‘Oh, my God, is this really happening?’”

The result, at least for Frank, has been a new direction for his work, as well as some money to fund it. He and a few astronomy colleagues around the country formed the group Categorizing Atmospheric Technosignatures, or CATS, which NASA has since awarded nearly $1 million in grants. The ambition for CATS is to create a “library” of possible technosignatures. In short, Frank and his colleagues are researching what could constitute evidence that technological civilization exists on other planets. At this stage, Frank stresses, his team’s work is not about communicating with aliens; nor is it meant to contribute to research on extraterrestrial radio transmissions. They are instead thinking mainly about the atmospheres of distant worlds, and what those might tell us. “The civilization will just be doing whatever it’s doing, and we’re making no assumptions about whether anybody wants to communicate or doesn’t want to communicate,” he says.

This line of inquiry might not have been productive just a few years ago. But several advances have made the search for technosignatures feasible. The first, thanks to new telescopes and astronomical techniques, is the identification of planets orbiting distant stars. As of August, NASA’s confirmed tally of such exoplanets was 5,084, and the number tends to grow by several hundred a year. “Pretty much every star you see in the night sky has a planet around it, if not a family of planets,” Frank says; he notes that this realization has only taken hold in the past decade or so. Because there are probably at least 100 billion stars in the Milky Way galaxy, and an estimated 100 billion galaxies in the universe, the potential candidates for life — as well as for civilizations that possess technology — may involve numbers almost too large to imagine. Perhaps more important, our tools keep getting better. This summer, the first pictures from the new James Webb Space Telescope were released. But several other powerful ground- and space-based instruments are being developed that will allow us to view exceedingly distant objects for the first time or view previously identified objects in novel ways. “With things like J.W.S.T. and some of the other telescopes, we’re beginning to be able to probe atmospheres looking for much smaller signals,” Michael New, a NASA research official who attended the 2018 Houston conference, told me. “And this is something we just couldn’t have done before.”

As Frank puts it, more bluntly: “The point is, after 2,500 years of people yelling at each other over life in the universe, in the next 10, 20 and 30 years we will actually get data.”

Credit…Illustration by Somnath Bhatt

In July, when NASA released the first batch of images from the Webb telescope, we could glimpse remote corners of the universe with newfound clarity and beauty — a panorama of “cosmic cliffs,” 24 trillion miles tall, constructed from gas and dust, for instance. The images were stunning but also bewildering; they defied description. What could we even compare them to? Webb was reaching farther in distance and into the past than any telescope before it, collecting light from stars that in some cases required more than 13 billion years to reach us. We will need to acclimate ourselves to the task of constantly looking at — and interpreting — things we’ve never seen before.

The Webb telescope can look near as well as far. During its first year, about 7 percent of its time will be spent observing our own solar system, according to Heidi B. Hammel, an interdisciplinary scientist who worked on the telescope’s development. Webb can analyze the atmospheres of nearby planets like Jupiter and Mars using its infrared sensors. These capabilities can also be directed at some of the closest Earth-size exoplanets, like those surrounding the small Trappist-1 star, 40 light-years away.

One goal of that focus is to discern a biosignature — that is, an indication that life exists (or has existed) on those worlds. On Earth, a biosignature might be the discarded shell of a clam, the fallen feather of a bird, a fossilized fern embedded in sedimentary rock. On an exoplanet, it might be a certain ratio of gases — oxygen, methane, H₂O and CO₂, say — that suggest the presence of microbes or plants. Nikole Lewis, an associate professor of astronomy at Cornell University whose team has been approved for 22.5 hours of Webb observation time this year to look at Trappist-1e, one of seven planets circling the Trappist-1 star, told me that well before declaring the discovery of a biosignature, she would have to carefully determine the planet’s atmosphere and potential habitability. “First, we have to find out if there’s air,” she says, “and then we can ask, ‘OK, what’s in the air?’” She estimates that it would take three or more years of observing a system to be able to say there’s a biosignature.

Biosignatures and technosignatures point the same way: toward life. But for now, they are being pursued by two separate scientific communities. One reason is historical: The study of biosignatures — which began in the 1960s, within the new discipline of exobiology — has been receiving support from NASA and academic institutions for decades. But “technosignature” was coined only recently, in 2007, by Jill Tarter, a pioneering figure in astronomy who has spent her career conducting searches for alien transmissions. Jason Wright, a professor of astronomy and astrophysics at Penn State who is a member of Frank’s CATS group, says he thinks of Tarter’s idea as a “rebranding” of the search for extraterrestrial intelligence, which has long been relegated to the scientific fringe. “When Jill coined the phrase,” Wright told me, “she was trying to emphasize that NASA was looking for microbes and slime and atmospheric biosignatures, but technosignatures were really under the same umbrella.” Any search for biosignatures on a distant planet, Wright contends, would logically overlap the search for technosignatures, once it became time to explain unusual observations. Does a telescopic reading suggest a life-sustaining atmosphere? Or is it possibly a sign of technology, too? Scientists looking for biosignatures, in other words, may encounter marks of technology as well.

Wright, Frank and the rest of the CATS team are thus interested in atmospheric markers that would probably never occur naturally. One recent group paper, for example, written primarily by Jacob Haqq-Misra, a CATS member who works at the nonprofit Blue Marble Space Institute of Science, considers how the presence of chlorofluorocarbons, an industrial byproduct, would give a distinct spectral signal and could be picked up by Webb. Haqq-Misra was also the first author on a recent paper suggesting that an exoplanet with agriculture — “exofarms” — might emit telltale atmospheric emissions. Another paper, one written mainly by Ravi Kopparapu, a CATS member who works at NASA’s Goddard Space Flight Center, makes the case that the emission of nitrogen dioxide, an industrial byproduct, could signal the existence of alien technology. Those emissions might be observable by a NASA space telescope, known as LUVOIR (Large Ultraviolet Optical Infrared Surveyor), that is slated to be deployed after 2040. These scenarios — aliens running factories, say, or aliens riding tractors at harvest time — might seem unlikely, but the scientists working on technosignatures are comfortable with the low odds. “If we focus on what’s detectable, based on these instruments that we’re building, that’s really the fundamental question,” Haqq-Misra told me.

Read More About the James Webb Space Telescope

After traveling nearly one million miles to reach a location beyond the moon, the James Webb Space Telescope will spend years observing the cosmos.

  • First Images: In July, NASA released the first set of images captured by the telescope. Here are five things we learned from that spectacular slide show.
  • Closer to Home: The telescope can capture photographs not only of galaxies across the universe, but also of objects in our celestial backyard, including planets such as Jupiter.
  • A Very Different Lens: The woman who oversaw the creation of the camera used by the telescope discussed the excitement of seeing her team’s work come to fruition.
  • A Cosmic Horn of Plenty: “I haven’t been so entranced with a view of the heavens for a long time,” writes our cosmic affairs correspondent, stunned by the power of the telescope.

When I visited Wright at his office at Penn State in the spring, he made the case that technosignatures are not only more detectable than biosignatures, possibly, but also more abundant and longer lived. Consider Earth as an example, he said. Its technology already extends all over the solar system. We have junk on the moon; we have Rovers driving around Mars; we have satellites orbiting other planets. What’s more, several spacecraft — including two Pioneers, two Voyagers and the Pluto-probe New Horizons, all launched by NASA — are venturing beyond the edge of the solar system into interstellar space. Such technosignatures could last billions of years. And we’re only 65 years into the age of space exploration. An older civilization could have seeded the galaxy with thousands of technosignatures, which could make them easier to detect.

“Look, I’m truly agnostic about whether there’s even anything to find,” Wright said. In 1961, he pointed out, the astronomer Frank Drake presented what’s now known as the Drake Equation, which is made up of many variables and attempts to help calculate the number of intelligent civilizations elsewhere in the galaxy. But with so little data to plug in to the variables, there has yet to be any solution to the equation.

For Wright, Drake’s equation at least allows for a “plausibility” that something is out there. But is it life or complex life? Biosignatures, Wright said, are going to be “extremely challenging to detect — if they exist. So that’s two big ifs. It’s very possible that life is just so rare that there’s nothing within a kiloparsec for us to find.” But technology, he explained, could have started the same distance away — a kiloparsec is 3,261 light-years in distance — and moved closer to Earth over eons. It could be a traveling probe like one of our Voyagers or a systematic species migration; it could be an electronic signal, sent 3,250 years ago and, moving at the speed of light, just coming into our range.

“So we have a much bigger search radius for technology,” Wright said. “But also, perhaps complex life that builds technology is itself extremely rare, even when life forms.” He paused. “I don’t know,” he said. “What drives me is not the idea that we will find something in my lifetime. What drives me is that we’re not looking very well. And it’s too important a search, answering too important a question, not to do well.”

“The giggle factor” — that’s what anyone who does research on extraterrestrials is bound to encounter, according to Frank. As a graduate student in the ’80s, Frank was wary of the field as a career move. “I’d never worked in this before, I’d never published any papers,” he told me, referring to his pre-technosignature research. His reluctance was reinforced by the marginalization of the subject. Early on, in the 1970s, NASA had shown a willingness to fund radio-telescope searches for extraterrestrial activity. But the search for aliens aroused opposition. In 1978, Senator William Proxmire declared that taxpayers were being fleeced, a criticism NASA heeded by striking the search for extraterrestrials from its budget. The agency was willing to back survey projects again in the 1980s, but another senator, Richard Bryan, stopped the programs in 1993. “This hopefully will be the end of Martian hunting at the taxpayer’s expense,” Bryan said at the time.

Only recently has the stigma begun to wear off. At the urging of the Texas representative Lamar Smith (now retired), who was chairman of the House Science Committee, a bill was introduced in Congress for NASA to allocate $10 million to technosignatures. NASA quickly asked for a forum to get a clearer sense of what research was worth funding, positioning the effort as a departure from radio astronomy. “I was told the workshop had to be in a certain Texas congressional district,” Wright, who was asked to organize the Houston meeting, told me.

When Frank, who trained as a theoretical astrophysicist rather than an observational astronomer, attended the Houston meeting, he had been writing about how civilizations alter their planetary atmospheres. Because humans have changed our world so significantly through global warming — essentially by burning wood and fossil fuels — he had been wondering if this would happen everywhere. “When you pull back and think of the evolution of any planet, you find that what we’re going through may be a common transition that you do, or don’t, make it through,” Frank says. In his view, any species that expands and grows is probably going to create significant feedback effects on its planet. “Civilizations are basically focused on harvesting energy and putting it to work,” he says. “And there should be unintentional markers when you do that. You’re leaving traces.” You’re creating technosignatures. Such assumptions about energy generation and activity are mostly what guide the CATS group.

One day in early May, I sat in on their monthly meeting, which takes place online. Frank led the discussion from his office in Rochester. Wright joined from Penn State; Haqq-Misra from Delaware; Kopparapu from Maryland. Another team member, Sofia Sheikh, joined from San Francisco. A few other contributors tuned in, too. The first order of business was planning for a four-day technosignatures conference at Penn State, organized by Wright for late June, just weeks away. “This is the first time we’ll all be together, physically, since the 2018 meeting in Houston,” Frank said enthusiastically. “I think we want to advertise how much progress has happened.” He quickly mentioned the chlorofluorocarbons work, the exofarm paper and the visibility of nitrogen pollutants from afar.

When Kopparapu’s turn came, he explained the relationship of the team’s ideas to the specifications of current and future telescopes. Some next-generation projects involve ground-based instruments that are much more powerful and sophisticated than what exists today — for instance, the Giant Magellan Telescope (now under construction in Chile) and the Thirty Meter Telescope (planned for Hawaii). For the CATS group, the most important of these future missions include LUVOIR and HabEx (Habitable Exoplanet Observatory), multibillion-dollar space telescopes that, unlike Webb, are to be built and calibrated expressly for the study of distant Earth-like planets.

These devices — only one of which may be built — are two decades away from deployment, however, and for the time being exoplanet study will largely depend on Webb. Once a year, a call goes out for proposals from researchers who want to use the telescope. Fainter objects in the sky generally require more time, brighter objects less. “The competition for a slot is fierce,” Eric Smith, Webb’s program scientist, told me. Because so many requests are rejected — last year the telescope reviewed about 1,200 proposals and awarded time to 286 winners — the proposals have to be compelling. According to Smith, the competition is likely to become even greater in the coming years, now that the scientific community has seen what the telescope can do. Frank told me that he believes that his team, or other scientists taking a cue from his team’s technosignature research, are probably a few years away from making a formal request. “If we’re going ask for a hundred hours of James Webb time, we better have every possibility worked out,” he says. “They’re not going to give us that unless we’ve shown that this is exactly where to look, this is the signal-to-noise ratio we expect, and so on.”

In the CATS meeting, the brainstorming covered a mix of old and new ideas. The technosignatures field is open to looking for inspiration anywhere, even in concepts that might have appeared decades earlier in journals or in obscure conference proceedings before being dismissed or forgotten (a 1961 paper on interstellar laser communication, for example). At this meeting, there was talk of “service worlds,” where a civilization develops a nearby planet or moon not for habitation but for, say, energy harvesting. It is an idea sometimes contemplated in science fiction, but in this instance the notion first arose from a paper that a member of the CATS group co-wrote a few years ago. On a service world, terrain might be covered entirely with photovoltaic panels that reflect part of the light spectrum back into space — a reflection that could be discernible trillions of miles away. “A service world wouldn’t even have a biosignature,” Frank said. “It’s just a pure technosignature.”

Sheikh then mentioned something she had been thinking about lately: microplastic pollution in oceans, now an Earth technosignature. “You can see it if you scoop up a glass of water and look at it under a microscope, it’s very obvious in situ,” she said. “But is there any way to detect that remotely? So I just decided to check — it seemed kind of silly.” While reading academic papers, she told the group, she found that scientists are trying to spot plastic in our oceans using radar satellites. “So they’re using remote sensing to look for changes in viscosity of ocean water, which is indicative of microplastics, and it seems like it actually works.”

As the discussion wound down, Frank raised something else: oxygen and combustion as a technosignature. This in turn raised an issue about ocean worlds. Could they, he asked, produce species that develop technology? “If you can’t start a fire underwater, how does an oceangoing species learn to do metallurgy?” The question was not a whimsy. Many exoplanets are thought to be complete water worlds. Earth, about one third of which is land, might be an exception. The group debated where an ocean species could find energy. “Hydrothermal vents,” Haqq-Misra offered. Others suggested chemical reactions that produce heat without combustion.

Frank said he still wondered if fire in an oxygen-rich environment is a prerequisite to development. “That’s why we’re thinking about combustion,” he said. “You’re not going to start with nuclear power, right?”

“It just seems very anthropocentric,” Nick Tusay, a Penn State graduate student on the call, said. “Just because that’s the way we did it, does it mean everyone else would? What if you have a civilization of octopuses?”

The comment prompted Sheikh to share some links to academic studies. “There’s actually this cool literature about tool development and aquatic animals,” she said. Underwater tool development has been hard to observe, as she understood it, but it’s real, and it could mean that combustion is not the only route to sophistication. A number of species also use water pressure or bubbles — or other species — as tools. “I think there’s a lot to explore there,” she added.

Frank seemed inclined to put off the discussion until next time. Still, as the meeting ended, the comments demonstrated how challenging it can be for the team to conceptualize other worlds. Their conversation likewise suggested that we know far less than we might think about our own.

To imagine the unimaginable, Ravi Kopparapu told me one day, “we must reorient our minds.” The problem is that the technosignatures field relies, for now, on a small data set (a single planet: Earth) where we know a species has arisen that created gadgetry, made pollution and altered its atmosphere (dangerously so). The CATS members, Kopparapu says, understand this as a liability, but also as a requisite first step. “If you go to a party where you know hardly anyone,” Kopparapu says, “the first thing you do is go to someone that you recognize so you can start up the conversation.”

During my visit to Frank, he told me that as difficult as it is for humans to imagine alien species, imagining long time frames is equally challenging. Modern science as a discipline is only about 500 years old. The transistor, the building block of modern technologies, is around 75 years old. The first iPhone came out 15 years ago. How would a technological society evolve over 10,000 years? Over a million?

Frank notes that there may be many other ways to define a civilization beyond what his group has been focusing on. Rather than builders of big antennas, extraterrestrials could be more like trees in a grove, communicating through threads of fungi underground. Rather than creators of dirty power plants, aliens might be like octopuses using tools in ice-crusted oceans. Some theorists have even posited that an ancient society could discard matter altogether, choosing to supplant itself with a diaphanous and undying form of artificial intelligence. “I can imagine biologies that are much different; I can imagine minds that are much different,” Frank says. For civilizations that we can detect through our instruments, though, he is still convinced that the logical approach is to focus on energy and the consequences of its use.

He is not inflexible, though. Since the meeting in Houston, Frank told me, some of his old assumptions and biases have been challenged. This includes the possibility that our familiarity with Western technology can trap us. He and some of the CATS members have been influenced by critiques of the search for extraterrestrials — chronicled, in part, in a recent issue of The American Indian Culture and Research Journal — that challenge our tendency to view industry and gadgetry as the primary indicators of “advancement.” Frank pointed out that some Indigenous cultures regard the whole natural world as intelligent. He has become wary, too, of grand, deterministic anthropological narratives he once saw as persuasive: the idea that “we were egalitarian hunter gatherers, and then there was the agricultural revolution, and then came villages, which turned into empires, and that then led to capitalism and science.” A new book, “The Dawn of Everything,” by David Graeber and David Wengrow, argues that research data from the last 30 years doesn’t support a story of such linear advancement. It has persuaded Frank that different and unpredictable paths for social and political arrangements — and technology, too — are possible anywhere. He has begun to seek out historians, anthropologists, sociologists, biologists and futurists to help his group narrow the possibilities.

Kathryn Denning is an archaeologist at York University in Canada and a longtime contrarian voice in the extraterrestrial-search community. “The social evolutionary story of humans on Earth is not a simple, unilinear upward trajectory,” she told me recently. And we shouldn’t think of aliens that way either. Many societies on Earth have fallen apart and rebuilt from their ruins, Denning points out; and many have never sought to become conquerors. And yet public intellectuals have often rendered the future in ways that give their declarations of high-tech destiny — gleaming megacities and roving starships — an air of certainty.

We might ascribe that to cultural hubris. At the June technosignatures meeting at Penn State, many presentations were given over to the CATS work as well as “traditional” extraterrestrial research involving radio astronomy. But there were also Denning and Hilding Neilson, an Indigenous astronomer and astrophysicist from the Memorial University of Newfoundland. Neilson challenged the audience to think about how some Indigenous societies were at least thousands of years old — older than science itself. And yet he wondered if they were considered “advanced” by Western definitions. In the case of looking for life elsewhere, he remarked, “we’re really looking for ourselves in space.”

The CATS group appears to be able to avoid that trap. At the Penn State meeting, not long after Neilson’s talk, I wandered into a lounge and ended up listening to a coffee-break debate among Frank, Sheikh and Wright. They were discussing a lecture by a colleague who proposed to find a technosignature in the glow of sodium lights, commonly used in streetlamps. A strong-enough signal could be detectable through some telescopes if, say, an exoplanet were completely covered in urban development.

But any technosignatures idea must go through the gantlet of group skepticism. Frank and Sheikh wondered if sodium light would be used by a civilization that developed differently — perhaps their eyes would function in different parts of the spectrum. Or perhaps they would live underground? “If you’re a creature that can’t see, if you’re like a bat that used echolocation, would you even need lights?” Frank said.

“Would you even know you’re part of the galaxy and this larger world?” Sheikh asked.

“Would you even look up at the stars?” Frank added. “I mean, if you couldn’t see, would you even know they’re there?”

Frank turned to me. “That’s what’s so extraordinary about this,” he said, meaning the maze he and the group wander through. They have to rethink evolution, technology, culture and the meaning of intelligence. “But you always have to come back to the fact that we’re building a telescope,” he added. “What sensors should it have to find a technosignature?”

He laughed, seemingly at the sheer number of details that would someday need to be worked out. “Also, what screws should it use — flat head, Phillips head or hex nut?”

Officially, NASA considers the work on technosignatures to be “high risk, high reward.” The risk, in dollars, is modest for now: The amount allocated by the agency is minuscule in comparison to, say, the $93 billion being invested over the next few years in its Artemis moon mission. But moving on to a next step, which would mean devoting precious time for technosignatures research on a telescope like Webb, or building an entirely new space-based instrument, would involve a sizable investment. As for rewards, the development of a technosignatures discipline might mirror that of astrobiology, which arose 25 years ago in response to the discovery of exoplanets. In contemplating biosignatures, astrobiologists gained new knowledge into how basic life on Earth can endure in extreme environments — under icecaps, for example, or near hydrothermal vents. Thinking about far-off things yielded insights close to home.

The ultimate success for the technosignature team would be an instance of someone using the CATS research to identify signs of a technological civilization. “That would be like the dog who is running and catches the car,” Kopparapu told me. What would we do next?

He and Frank both think it’s possible that we would do … nothing. At least not right away. While there exists a growing body of literature about “first contact” protocols, we might just monitor a distant technosignature for decades, or perhaps centuries, taking readings with increasingly better telescopes. And then — maybe — we might send a space probe or message. Because distances are so vast, it’s not lost on the researchers that in viewing an apparently bustling exoplanet from, say, 50 light-years away, we would see the spectra of technology from 50 years earlier. To send an electronic message and receive a response would, at best, take 100 years. An actual journey could take millenniums.

But the work may turn out to have utility beyond a contact scenario or headline-grabbing discovery. Since the 1950s, one of the defining ideas in the search for extraterrestrials has been the Fermi Paradox, named after the Italian American physicist Enrico Fermi. Essentially, it asks why, in a universe packed with stars and planets, we have yet to see evidence of life beyond Earth. One possible explanation is that life is rare or even unique to Earth. Another is that intelligent beings exist elsewhere but prefer not to make themselves observable. But there is a resolution to the paradox that is more unsettling: An idea known as “the great filter” posits that there are difficult, perhaps impassable, points in any species’ evolution. That filter might kick in early, as complex life begins, or later, when technology produces dangerous rebound effects. Either way, a result would be eerie cosmic silence.

Rebecca Charbonneau, a science historian at the National Radio Astronomy Observatory who attended the Penn State technosignatures conference, told me that in the mid-1960s, not long after Drake came up with his equation, Carl Sagan, a close friend and colleague of his, asked, “Do technical civilizations tend to destroy themselves shortly after they become capable of interstellar radio communications?” Charbonneau says that the specter of nuclear annihilation probably shaped that era’s views. But while the agents of destruction may have changed, the fear remains. We can glimpse an updated version of how things might end in our warming atmosphere, in our world’s shocking declines in biodiversity.

In a sense, this makes the search for technosignatures a search for sustainability as well. “Any society that’s long-lived on geological or astronomical time scales is by definition sustainable,” Michael New, the NASA administrator, told me. But the fact that a society avoided reducing its impact on the geology and chemistry of its home, he says, might hold a key to how they avoided self-destruction. “It may also be that really successful technological societies at some point become hard to detect,” he says, “because they’re living in more or less equilibrium with their planet.”

This last point is being debated within Frank’s group, too; they don’t want to overlook technosignatures because they don’t fit ideas of what they should be looking for. Sofia Sheikh gave me an example: the first European settlers to California. “There are good records, primary sources from the time, that say that they were like, ‘Oh, it’s like a wonderland out here, you can just walk through the forest and there’s no undergrowth, there are just fruit trees growing naturally everywhere.’ But what they were seeing was not a natural process — it was the result of centuries of tending of the land by Indigenous groups.” These were technosignatures, she said, resulting from advanced agricultural techniques that stopped wildfires from breaking out — but Europeans didn’t recognize them. “And so we don’t want to see something astronomically and be like, ‘Wow, isn’t it cool that the universe did that?’ just because it doesn’t fit our idea of a resource-consuming, technological civilization.”

And yet, it’s also possible that years from now — after all the arduous and careful searching — even a total absence of cosmic evidence could prove valuable. Two CATS members, Haqq-Misra and Kopparapu, recently considered how the coming age of observations for biosignatures and technosignatures might shed light on the great filter. “If we find biosignatures, that means there’s a bunch of planets that can have life on them,” Haqq-Misra told me. But if we find plentiful signs of life but no signs of technology, that’s more worrisome. It could mean the odds are against technological civilizations sustaining themselves. They may be exceedingly rare — or tend to self-destruct.

“On the other hand,” Haqq-Misra added, “what if we find technosignatures everywhere? That’s actually encouraging. That means that it’s possible to have technology in a long-term, sustainable balance with your planet.”

Would the data, I asked — assuming we ever find it — tell us how to become sustainable or how to remain sustainable? No, Haqq-Misra said. “Just that it’s possible.” As for getting there, we would still be on our own.


Jon Gertner has been writing about science and technology for the magazine since 2003. His most recent article was about high-containment biolabs and their vulnerabilities in a pandemic-era world. Somnath Bhatt is an artist and a designer in New York who was born and raised in Gujarat, India. He is known for his use of symbolic and ritualistic pixelated drawings.

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