If extraterrestrial civilizations exist with technology similar to ours, could they detect Earth? A team of SETI researchers explored this by analyzing Earth’s technosignatures—signals that indicate technological activity.
A team of researchers, led by Dr. Sofia Sheikh of the SETI Institute and working with the Characterizing Atmospheric Technosignatures project and the Penn State Extraterrestrial Intelligence Center, set out to explore a fascinating question: If an alien civilization had technology similar to ours, could they detect Earth and signs of human activity? If so, what signals would stand out, and how far away could they be spotted?
Using a theoretical, model-based approach, this study is the first to examine multiple types of technosignatures together rather than separately. The findings show that Earth’s most detectable signals come from radio emissions—particularly planetary radar, such as those once transmitted by the Arecibo Observatory. These signals could potentially be detected from as far as 12,000 light-years away.
The Role of Atmospheric Technosignatures
Other technosignatures, such as atmospheric pollutants, are also becoming more detectable thanks to advances in telescopes like the James Webb Space Telescope and the upcoming Habitable Worlds Observatory (HWO). If an alien civilization were searching with technology comparable to HWO, they might detect nitrogen dioxide emissions from Earth at distances of up to 5.7 light-years—just beyond Proxima Centauri, our closest stellar neighbor.
Finally, as you get closer and closer to Earth, you would detect more and more human-made signatures simultaneously, including city lights, lasers, heat islands, and satellites, offering a comprehensive view of our technological presence.
Reflections on Earth’s Visibility
“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,” said Macy Huston, co-author and postdoc at the University of California, Berkeley, Department of Astronomy. “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.”
“One of the most satisfying aspects of this work was getting to use SETI as a cosmic mirror: what does Earth look like to the rest of the galaxy? And how would our current impacts on our planet be perceived,” said Sheikh. “While of course we cannot know the answer, this work allowed us to extrapolate and imagine what we might assume if we ever discover a planet, with, say, high concentrations of pollutants in its atmosphere.”
How SETI Searches for Alien Technology
SETI scientists search for advanced alien civilizations by looking for signs of technology — signals or patterns that cannot be explained by natural phenomena that may indicate intelligent life. These signals are called technosignatures and come in various forms. Radio telescopes are the most commonly used tool for SETI searches. Researchers also use optical telescopes to scan for laser pulses that could indicate communication or propulsion patterns. Another approach involves studying the atmospheres of exoplanets in habitable zones around stars to look for chemical signatures that might suggest life or industrial activity. SETI scientists also consider technologies far beyond those currently invented on Earth, such as Dyson spheres, but these far-future technologies were not considered in this study.
Shaping the Future of SETI
This study demonstrates how Earth’s technosignatures can provide a multiwavelength framework for understanding the detectability of technology on other planets and shaping our search for intelligent life beyond Earth. Future telescopes and receivers could enhance our detection sensitivity or enable us to identify new types of technosignatures, such as other atmospheric signatures of pollution. Repeating this type of study over the years as astronomical technology advances and the human impact on the planet evolves could provide fresh insights and refine our approach to discovering extraterrestrial life.
This paper appears in the Astronomical Journal article “Earth Detecting Earth: At What Distance Could Earth’s Constellation of Technosignatures be Detected with Present-day Technology? ” by Sheikh et al.
Reference: “Earth Detecting Earth: At What Distance Could Earth’s Constellation of Technosignatures Be Detected with Present-day Technology?” by Sofia Z. Sheikh, Macy J. Huston, Pinchen Fan, Jason T. Wright, Thomas Beatty, Connor Martini, Ravi Kopparapu and Adam Frank, 3 February 2025, The Astronomical Journal.
DOI: 10.3847/1538-3881/ada3c7
