Pollution may lead us to alien civilizations, NASA researchers suggest

NASA scientists have proposed searching for advanced extraterrestrial civilizations among the stars by looking for a specific kind of pollution associated with combustion and, therefore, most likely some form of technology.

In a new study, the team at NASA’s Goddard Space Flight Center suggests hunting for the presence of nitrogen dioxide gas (NO2), produced here on Earth through the burning of fossil fuels in addition to naturally-occuring forms of the gas, among the roughly 4,000 potentially habitable exoplanets humanity has thus far identified.

“In the lower atmosphere (about 10 to 15 kilometers or around 6.2 to 9.3 miles), NO2 from human activities dominate compared to non-human sources. Therefore, observing NO2 on a habitable planet could potentially indicate the presence of an industrialized civilization,” says Ravi Kopparapu of NASA’s Goddard Space Flight Center. 

These distant exoplanets, worlds orbiting stars other than our sun, are the most likely candidates humanity has yet encountered that could be home to technological civilizations, but given the distances involved, it's extraordinarily difficult to just send a probe to investigate them. 

Instead, SETI (Search for Extra-Terrestrial Intelligence) researchers listen for distant communications signals and watch for optical messages with giant telescopes here on Earth and out in space in our solar system. They also hunt for extraterrestrial artifacts and technosignatures, like the remains of a Dyson Sphere built around a distant star for power, for example.

Now, NASA scientists are proposing looking for signs of pollution, similar to that found in the atmosphere of our own planet, as a potential technosignature we may hitherto have been overlooking in our search for intelligent life out there in the universe. 

"NO2... is a general byproduct of any combustion process," the researchers argue, meaning that, instead of hunting for human-centric pollution like chlorofluorocarbons (CFCs), the result of our own technological development, scientists could look for something more universal to processes likely to at least get a technologically advanced civilization going, like the traces of combustion. 

The NASA researchers used computer models to predict whether NO2 pollution would be a practical means of detecting technologically advanced life beyond our own, using our current and next generation telescopes, as NO2 strongly absorbs very specific wavelengths of visible light.

They found that, with 400 hours of observations, a civilization producing the same amount of NO2 as our own could be detected on an Earth-sized planet 30 light-years away. 

“On Earth, about 76 percent of NO2 emissions are due to industrial activity,” says Giada Arney of NASA Goddard, who added that the method would need to be refined but could bolster other efforts to detect life out there in the cosmos. 

Rather than merely scanning the skies for the presence of NO2, it is conspicuously elevated levels that SETI researchers might look for to indicate the presence of civilizations out there among the stars, with the hope being that they’re still alive and breathing by the time we can make contact.

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