What if out there in the vastness of space there was an alien civilization so advanced that it could scan our galaxy for signs of intelligent life? What traces of our passage could it detect, what technological imprints of our progress would reveal the existence of humanity?
It is precisely from this intriguing speculation that a theoretical study conducted by a team of researchers led by Sofia Sheikh of the SETI Institute, which attempted to overturn the perspective of the search for extraterrestrial intelligence, imagining the Earth under the lens of hypothetical alien observers.
Technosignature: The Fingerprints of Advanced Civilization
At the heart of the study, published in the Astronomical Journal (I link it here), there is the concept of technosignature, or those distinctive signs that a technologically advanced civilization leaves in space, like a sort of "fingerprint" of its passage. Radio signals, nitrogen dioxide emissions, artificial lights, heat islands: these are just some of the traces that, according to researchers, could reveal the existence of humanity to a hypothetical alien observer.
“One of the most satisfying aspects of this work has been using SETI as a cosmic mirror,” Sheikh explained. “What does Earth look like to the rest of the galaxy? And how would our current impacts on our planet be perceived?” Fascinating questions, which force us to think not only about our place in the universe, but also about the imprint we are leaving on our world.
Radio signals, our “lighthouse” in space
By analyzing the various technosignatures, the researchers discovered that powerful radio signals, such as those once emitted by the Arecibo radio telescope (now no longer operational), would be the most evident traces of our presence, potentially detectable up to 12.000 light-years away. A true cosmic “lighthouse”, capable of attracting the attention of any advanced alien civilizations.
Other significant footprints would be emissions of nitrogen dioxide, a gas produced by human activities, which our current instruments (such as the future Habitable Worlds Observatory) could detect up to 5,7 light years away, beyond the closest star to the Sun. And then, as we get closer to Earth, a hypothetical alien observer might see other traces of our presence, such as satellites, lasers, heat islands, and city lights.
A constellation of technosignatures
“Our goal with this project was to bring SETI back down to earth for a moment and reflect on where we really are today with Earth's technosignatures and detection capabilities,” explains Macy Houston of the University of California, Berkeley, a co-author of the study. “In SETI, we should never assume that other life and technology would be just like ours, but quantifying what ‘ours’ means can help put SETI searches into perspective.”
In a sense, the researchers say, Earth has a true “constellation of technosignatures,” with more and more elements becoming visible as a hypothetical observer gets closer. A fascinating concept, which pushes us to think about how we would appear to another civilization and what our “technological portrait” would reveal about us.
Signs of Advanced Civilization, a Cosmic Mirror for the Future
While it is unlikely that there is a true “sister Earth” out there, with a civilization entirely similar to ours, the authors of the study believe that analyzing our technosignatures can provide valuable insights to refine our strategies for searching for extraterrestrial intelligence. In a sense, looking at ourselves “from the outside” can help us better understand what to look for in deep space.
“In SETI, we should never assume that other people’s life and technology would be just like our own, but quantifying what ‘ours’ means can help put SETI searches into perspective,” Huston said. In short, studying Earth as another advanced civilization would see it can be a way to sharpen our “cosmic senses” and prepare for the theoretical possibility of intercepting signals from another civilization (by the way: if it happened, what would we do??).
Science fiction? Maybe. But then again, as the great astrophysicist loved to repeat Carl Sagan, “somewhere, something incredible is waiting to be known.” And who knows, as we scan the skies for signs of other civilizations, we may end up discovering something new about ourselves and our place in this vast, mysterious universe.
