A team of NASA scientists is taking a clever approach to hunting for alien life: scanning exoplanets for signs of air pollution.

Just as pollutants like nitrogen dioxide and greenhouse gases in Earth’s atmosphere are an indication of human activity below, a team of NASA researchers are now looking for pollutants on other, potentially-habitable exoplanets as a new alien technosignature, meaning a sign of an advanced extraterrestrial civilization. Their study, posted online and accepted for publication in The Astrophysical Journal, is the first to add nitrogen dioxide as a potential technosignature — giving scientists a new tool in the search for life.

The idea of sniffing out aliens based on their pollution isn’t a new one. But adding nitrogen dioxide, a byproduct of burning fossil fuels in power plants or vehicle engines, helps broaden the search.

“Therefore, observing [nitrogen dioxide] on a habitable planet could potentially indicate the presence of an industrialized civilization,” lead study author Ravi Kopparapu, a researcher at NASA’s Goddard Space Flight Center, said in a press release.

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