Despite these obstacles, scientists have developed a new theory that may help us track down other civilizations living in the cosmos — a theory centered on pollution. Specifically, by searching for nitrogen dioxide gas. According to The Independent, scientists working for NASA have begun seeking out planets that show signs of pollution by looking for nitrogen dioxide. Ravi Kopparapu, a scientist working at NASA’s Goddard Space Flight Center in Maryland, described the new thinking this way (via CNET): “On Earth, most of the nitrogen dioxide is emitted from human activity — combustion processes such as vehicle emissions and fossil-fueled power plants.” Because of this, NASA is now using nitrogen dioxide as what they call a “technosignature” — evidence that points to a potential industrial civilization.

While the theory seems sound, the tricky part lies in detecting nitrogen dioxide from planets that are many light-years away. According to The Independent, scientists were able to determine — with the help of computers — that nitrogen dioxide gas absorbs colors from our visible light spectrum. So, in theory, scientists need only look for the light signature that nitrogen dioxide produces to determine if an alien civilization has at some point gone through an Industrial Revolution of its own.