Can Alien Smog Lead Us to Extraterrestrial Civilizations?

A new study modeled whether we could find intelligent life on another planet—by looking for its pollution.

“Last March, when Ravi Kopparapu was still working from his desk at the Goddard Space Center in Maryland, he came across a press release from NASA’s Earth Observatory. Levels of Nitrogen dioxide (NO₂) had plummeted over China since the country of 1.4 billion instituted strict stay-at-home orders more than a month earlier. He texted his colleague Jacob Haqq Misra with the link: “Technosignature?” he wrote. “Oh interesting!” Haqq Misra replied.

The observations had piqued Kopparapu’s interest, and two months later, still thinking about the ways that modern societies pollute their planet’s air, he read a paper on the effect of pandemic-related public health measures on atmospheric pollution. Researchers found the same effect playing out in other highly industrialized nations, like South Korea and the United States. The level of NO₂ over urban centers decreased by between 20 and 40 percent from January to April 2020, when many governments were following China’s lead and mandating that citizens stay at home. Nitrogen dioxide is one of the more prevalent pollutants, a result of combustion and fossil fuel use as well as natural biological processes like soil emissions and lightning. But Kopparapu wasn’t interested in NO₂ because of its effect on Earth. His focus was light-years away, in the atmospheres of the more than 4,000 known exoplanets in our region of the Milky Way galaxy.”