We May Find Aliens, If They Have Polluted Their Own Planet
Have other intelligent beings polluted their environment? Harvard researchers are tentatively making this assumption in their new avenue in the search for intelligent extraterrestrial life.
Recently, the search for intelligent life in the universe has mostly revolved around the detection of electromagnetic emissions such as radio waves. In a recently published paper, physicists from the Harvard-Smithsonian Center for Astrophysics proposed an alternative: in the search for extraterrestrial life, we should search for signs of industrial pollution in Earth-like planets' atmospheres. According to the paper, the "fingerprints" of certain pollutants can be spotted with our current technology under ideal conditions, and if these pollutants are found, they could indicate the presence of technologically advanced beings.
"We consider industrial pollution as a sign of intelligent life, but perhaps civilizations more advanced than us, with their own SETI programs, will consider pollution as a sign of unintelligent life since it's not smart to contaminate your own air," said Harvard student and lead author of the paper Henry Lin.
The abstract of the paper states, "Detecting biosignatures, such as molecular oxygen in combination with a reducing gas, in the atmospheres of transiting exoplanets has been a major focus in the search for alien life. We point out that in addition to these generic indicators, anthropogenic pollution could be used as a novel biosignature for intelligent life. To this end, we identify pollutants in the Earth's atmosphere that have significant absorption features in the spectral range covered by the James Webb Space Telescope."
Co-author Avi Loeb made this awesomely corny pun: "People often refer to ETs as 'little green men,' but the ETs detectable by this method should not be labeled 'green' since they are environmentally unfriendly." That being said, there are also theories that an extremely advanced race of alien may intentionally pollute the environment and cause global warming on a planet that would otherwise be too cold to sustain life.
Their tool of choice, the James Webb Space Telescope (JWST), can detect certain ozone-destroying chemicals in the atmospheres of other planets, provided that they are ten times the levels on Earth. The only significant limitation to using the JWST is the fact that it can only detect these chemicals on planets that orbit white dwarfs, which are essentially dead Suns. In order to find these biosignatures on planets that orbit live stars that are comparable to our Sun, we would need a much more powerful telescope.
According to the authors of the paper, this technique could not only lead us to current alien civilizations, but also civilizations that have long since destroyed themselves. Certain pollutants can survive in the atmosphere for 50,000 years, which means we may discover a planet that held intelligent life that proceeded to wreak havoc on their environment and go extinct.
"In that case, we could speculate that the aliens wised up and cleaned up their act. Or in a darker scenario, it would serve as a warning sign of the dangers of not being good stewards of our own planet," said Loeb.