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 —
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.”
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.
by Jon Gertner, NY Times |
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