If an extraterrestrial civilization existed with Earth-like technology, would they be able to detect Earth and evidence of humanity? If so, what signals would they detect and from how far away? A new study by a team that includes Penn State astronomers and alumni used a theoretical, modeling-based method to investigate Earth's detectability from across the cosmos, which the team said could help shape efforts in the search for extraterrestrial intelligence (SETI).
The study was recently published in the Astronomical Journal.
"One way we can look for alien civilizations is to look for signs of their technology," said Pinchen Fan, doctoral student in astronomy, astrophysics and astrobiology in the Penn State Eberly College of Science and an author of the paper. "These 'technosignatures' can take a variety of forms, from radio and optical signals to chemical signatures in a planet's atmosphere - any kind of signal or pattern that can't be explained by natural phenomena that could indicate intelligent life. In this study, we explored the wide range of our own technosignatures that could be detected at various distances from Earth with our current technology."
The study is the first to analyze a wide range of Earth's current technosignatures together in a consistent manner to determine their relative detectability. The researchers calculated the ability to detect those signals with current Earth-like technology if they were coming from space.
The researchers found that radio signals, such as planetary radar emissions from the former Arecibo Observatory, are Earth's most detectable technosignatures, potentially visible from up to 12,000 light-years away. Because radio signals are widely used on Earth and because they can travel such long distances, radio telescopes are the most commonly used tool for SETI researchers.
Atmospheric technosignatures - chemical signatures in a planet's atmosphere that might suggest life or industrial activity - were the next most detectable sign of life. Emissions from compounds like nitrogen dioxide have become more detectable than they were a decade ago, thanks to advances in instruments like the James Webb Space Telescope and the upcoming Habitable Worlds Observatory (HWO). A civilization with technology like HWO could detect these emissions from as far as 5.7 light-years away, just beyond our closest stellar neighbor, Proxima Centauri.
Finally, getting closer and closer to Earth, an advanced civilization would detect more and more human-made signatures simultaneously, including city lights, lasers pulses that could indicate communication or vehicle propulsion patterns, clusters of heat given off by cities called heat islands, and satellites, offering a comprehensive view of our technological presence.
