科学美国人60秒:Air Pollution Could Reveal ET's Home

Searches for extraterrestrial intelligence have focused on various signs of life. And one signature of alien intelligence may be, cough, cough, air pollution.
 
NASA’s James Webb Space Telescope, due to launch in 2018, should be powerful enough to detect chlorofluorocarbons, CFCs. These ozone-destroying chemicals are used in aerosol sprays on Earth. Maybe another planet’s denizens also employ them.  
 
A new analysis of this idea notes that aliens would have to be heavy users. The Webb scope could only detect the chemicals if they were 10 times more prevalent than here on Earth. And even then, the planet would have to orbit a special kind of star, a white dwarf, for the CFCs to show up. White dwarfs—the ultimate destiny of stars like the sun—maximize the pollution signal.
 
The study is in the Astrophysical Journal. [Henry W. Lin, Gonzalo Gonzalez Abad and Abraham Loeb, Detecting industrial pollution in the atmospheres of Earth-like exoplanets]
 
CFCs could hang around in a planet’s atmosphere for a long time. So if an extraterrestrial civilization wised up and stopped polluting, we might still see the effects. Even a society that managed to destroy itself long ago could leave a chemical trace. Let’s hope that’s not how they discover us.
 
—Clara Moskowitz