According to new studies, aliens could be identified by analysing air emissions on other planets. The presence of nitrogen dioxide gas, which is generated on Earth by burning fossil fuels, was explored in a report by the space agency. Although the development of a society that has transformed into oil or coal-based industries tends to be slow, gas is often extracted from other materials, including lightning and biological processes. Ravi Kopparapu of Nasa's Goddard Space Flight Center in Greenbelt, Maryland, said, Most of the nitrogen dioxide on earth is emitted from human activities - combustion processes such as vehicle emissions and fossil-fueled power plants.
Compared to non-human sources, NO2 from human activities dominates in the lower atmosphere (approximately 10 to 15 kilometres or about 6.2 to 9.3 miles). Therefore, the existence of an industrialized civilization could theoretically be suggested by detecting NO2 on a habitable planet. Nitrogen dioxide gas may be what researchers call a "technology signature" when a gas is emitted as a by-product of an industrial operation. This is similar to biosignatures, which are gases formed by organic activity, such as oxygen and methane. Scientists need to use these signs - which can be measured at great distances - to determine which worlds are worth studying, because of the large number of planets in the universe, as well as their distance.