A brief guide to looking for aliens

“In principle, in the Solar System, we can look for life just as life,” Wright says. Will Europa Clipper spy an extraterrestrial whale breaching the icy ocean of one of Jupiter’s moons? It could, but the odds are... long. If the probe does find evidence of life, that data will probably be in the form of a chemical signature of life, like “some byproduct of metabolism [or] some sort of alteration of chemical equilibrium that indicates that there's a living biosphere,” Wright explains. The example he offers is finding methane on Mars.

The search for such evidence, called "biosignatures," is one of the main ways that researchers are looking for extraterrestrial life. A team of researchers has already booked more than 200 hours of time on the James Webb Space Telescope to examine the atmosphere of a tantalizingly Earth-like exoplanet called TRAPPIST-1e for signs of methane or carbon dioxide. 

Wright and his colleagues are taking a different approach. “It’s one step removed from biosignatures," he says. “We're looking for the byproducts of technology."

Technology leaves louder evidence than life itself

These “technosignatures” take a lot of different forms.

In one scenario, extraterrestrials might be sending messages to us — or to whoever comes across them — on purpose. It’s not as far-fetched as it might sound. For our part, humans have sent deliberate messages out into space on several occasions. In the 1960s, scientists in the Soviet Union sent transmissions to Venus as a means of testing a new radar system. In 1972, American scientists sent messages to a star cluster called Messier 13. Both of these efforts were mostly symbolic, though. The American signals won’t reach their destination for 25,000 years. By that time, Messier 13 will have moved out of their path.

“If [extraterrestrials are] sending messages very loudly to Earth to get our attention, that would be the easiest to detect,” Wright says. “But even if it's not intended for us, we can tell something's very different [about the signal], even if we can't decode the message if they're communicating,” he says.

That’s because researchers think they could easily tell the difference between radio waves created by technology and similar transmissions emitted from natural sources, like stars and nebulae.

“Radio waves from technology look nothing like radio waves from nature. We would never mistake one,” he emphasizes. “That's why it's such an attractive way to go looking for life.”

One key difference is timing. Radio waves from technology “have the capacity to be extremely brief,” he says. And “they have the capacity to be extremely narrowband.” In nature, a source of radio waves will typically cover a wide range of frequencies, but technology makes it possible for humans (and perhaps others) to home in a single wavelength.

“And if it's communication, it could be extremely information-rich,” he adds.

While the idea of intercepting extraterrestrial communications is tantalizing, Wright says it isn’t the most likely scenario. Instead, we're more likely to pick up on radio waves far-off civilizations are using for their own purposes. “Our loudest radio waves are probably from radar, they're not communicative at all,” he says. The same could very well be true of extraterrestrials. “If they use radar to track asteroids in their systems, you could detect that,” he says.

Radio waves aren’t the only technosignature that researchers could look for. Wright says extraterrestrials “might alter their atmosphere in some way with artificial compounds like we do.” One example is the chlorofluorocarbons that humans pumped into the air relentlessly from the late 1800s until the end of the twentieth century when an international treaty led countries around the world to curtail their emissions of the planet-harming chemicals.

“If we were to see chlorofluorocarbons in another atmosphere, that would be a very good indicator that, that there was some sort of industry coming on that planet,” Wright adds.

Figuring out what to look for is no small task

One big reason that researchers have spent so much time thinking about what they might find is that it's impossible to go looking for everything at once. A systematic search has to be based on at least a hazy idea of what the extraterrestrials might actually be doing. Without much (read: any) data from any form of life beyond our planet, that's no small task.

“It’s important to… think about how life might evolve to use technology and what kind of technology might come about,” Wright says. "We don't want to make the mistake of assuming that their technological trajectory will look like that of, say, Western Europe.”

He points to the Fermi Paradox as the most famous argument in the search for extraterrestrials — and one that’s indeed based on a lot of assumptions about how a technologically advanced society might behave.

In brief, that position holds that advanced extraterrestrial societies must not exist because if they did, they would have figured out interstellar travel. And if a society had figured out how to travel beyond its home solar system, “they surely would have colonized all of the stars in the galaxy by now,” Wright says. Since the aliens aren’t already on Earth, they must not exist at all.

“By the numbers, it's a powerful argument,” he says. “There's been plenty of time for an aggressively expanding species to have populated every star system in the galaxy if they like.’

But there’s a problem. The paradox (which got its name from an off-hand comment by Enrico Fermi, who was more interested in nuclear physics than astrobiology) takes a lot for granted.

Science is limited by scientists' own stereotypes

“There are a lot of assumptions baked in there about the natural trajectory of life: that it will spread, that [extraterrestrials] will stay where they go, [and] that we would have noticed them if they were in [our] solar system,” Wright says.

Those assumptions aren’t generalizable to all groups of humans, so they definitely aren’t generalizable to all living things. Wright says such perspectives “have pervaded and still pervade a lot of the work.”

“Those [ideas] are often based on stories of European colonization, as opposed to more realistic stories about human migration, [such as] hominid migration out of Africa or the peopling of the Pacific thousands of years ago, which might be better analogies,” he remarks.

Anthropologists help in the search for extraterrestrial life by offering “an arm’s length perspective” on humans. They can tell astrobiologists “you're not just projecting human patterns on the aliens and saying they'll follow [those patterns]. The patterns [astrobiologists] are talking about aren't even universal in humans and might not even describe any reality on Earth,” Wright says.

Indigenous scholars have made similar observations. In fact, the most recent issue of the American Indian Research and Culture Journal was a special issue dedicated to research examining the search that Wright and colleagues across the field are undertaking.

It's a big if

What would it be like if researchers did come across evidence of aliens? Wright says proof positive could come in a lot of different forms. 

"It could be super boring," he assumes. For instance, researchers could detect a faint radio signal from a faraway galaxy that's clearly from an artificial source but too far away to investigate any further. "And that's all we ever know," he says. "It's not world-altering, it's just 'oh, look at that."

Even in that kind of situation, the first thing any self-respecting researcher would do is show the data to colleagues and ask those with the right equipment to independently verify the signal. With any luck, the signal would endure for an extended period of time, long enough for multiple research groups to study it. That's key to doing good science "because if it's just one thing you've recorded once, and then it never happens, again... there is nothing you can do with it," he discloses.

"On the other hand, if we find like an alien planet in the Solar System, that's a whole different set of things to manage."