Hunting for Technosignatures

Beyond radio, scientists search for technosignatures — any observable trace of technology. A civilization using vast amounts of energy might build a Dyson sphere around its star, detectable as an unusual infrared excess. Industry might leave atmospheric pollutants like chlorofluorocarbons in an exoplanet's spectrum. Artificial night-side lights or non-natural spectral lines could also give a civilization away. The hard part is telling real technosignatures from natural phenomena that mimic them — surveys for Dyson spheres have turned up a few intriguing candidates but no confirmed detections.