Scientists are pouring their resources into searching for signs of life on other planets -- but how might extraterrestrial life find us? An experiment spearheaded by the SETI Institute studies how alien societies might theoretically use Earth's "technosignatures" to locate human life. The project reveals not only the diverse ways in which we humans make our existence known, but also which signatures might lead intelligent life to our celestial doorstep most effectively.
The experiment, led by SETI's technosignature research scientist Sofia Sheikh, with assistance from the Penn State Extraterrestrial Intelligence Center, begins with a few key assumptions. First, the extraterrestrial life in question would come from a "mirror Earth": a planet just like our own, but halfway across the galaxy. Second, the experiment assumes that the intelligent life on this mirror Earth possesses the same technology we do, and has used it for the same amount of time as humans have. Rockets, satellites, radio telescopes, infrared observatories, and so on are all fair game -- they just can't be more advanced than our own.
Much in the way Earthly scientists use these technologies to hunt for signs of life within and beyond our galaxy, SETI's hypothetical extraterrestrials would use all of the above to search for alien (to them) technosignatures, or signs of technology that could indicate the existence of intelligent life.
In a release published Monday, SETI noted that Earth's planetary radar signals (like those from the now-defunct Arecibo Observatory) would likely be spotted first, as they're detectable from 12,000 light-years away. Next up would be radio signals from NASA's Deep Space Network, or DSN. Atmospheric nitrogen dioxide would be roughly as visible as lasers and LTE radio (but only because SETI's aliens would have advanced their observatories alongside our James Webb Space Telescope and forthcoming Habitable Worlds Observatory) with city lights and heat islands coming from behind. Transiting satellites would only be detectable from about 140 million miles away -- the amount of space lurking between Earth and Mars.
"Our goal with this project was to bring SETI back 'down to Earth' for a moment and think about where we really are today with Earth's technosignatures and detection capabilities," Macy Huston, astrophysicist and study co-author, said. "In SETI, we should never assume other life and technology would be just like ours, but quantifying what 'ours' means can help put SETI searches into perspective."
SETI's experiment joins a growing list of analyses that examine Earth and its intelligent life (believe it or not, that's us) from an extraterrestrial point of view. Last year, the European Space Agency's JUICE spacecraft confirmed that Earth is habitable on its way to Jupiter. A few years earlier, researchers at the Johns Hopkins Applied Physics Laboratory flipped the transit method -- which scientists had used to find exoplanets for more than two decades -- on its head by asking how it might be used to locate Earth from another planetary body.
Overall, these studies tell us that unless we truly are alone in the universe, it won't be a matter of if we come into contact with extraterrestrials; instead, the question will be whether humans or ETs say hello first.