According to a new study by NASA specialists, an extraterrestrial technologically advanced civilization can be detected by atmospheric pollution. At the same time, scientists call nitrogen dioxide the main signature. This is reported in an article published on the arXiv.org preprint repository.
A possible sign of life (biosignature) could be a combination of gases such as oxygen and methane. Likewise, the presence of technology can be identified by nitrogen dioxide, which is a by-product of combustion in industrial processes. Another possible sign of an extraterrestrial civilization could be chlorofluorocarbons (CFCs), which are also powerful greenhouse gases suitable for terraforming. CFCs are not produced by living organisms, but they are produced in very specific processes.
Scientists have modeled whether nitrogen dioxide pollution can create a signal that can be captured with existing and planned telescopes. This substance is capable of absorbing some wavelengths of light reflected from the planet. It turned out that if an extraterrestrial civilization produces as much nitrogen dioxide as mankind is currently producing, it could be detected 30 light-years away within 400 hours of observation with one of the space telescopes scheduled to launch.
Stars that are colder and much more common than our Sun, such as type K and M stars, will produce a stronger and more easily detectable NO2 signal. These stars emit less ultraviolet light, which can destroy nitrogen dioxide.