If Astronomers See These Chemicals in a Planet’s Atmosphere, There’s Likely an Advanced Civilization There
They suggest that technological civilizations might be uncovered via a hunt for chemicals not created by life. Specifically, the team proposes nitrogen trifluoride (NF3) and sulfur hexafluoride (SF6). 
https://www.universetoday.com/163240/if-astronomers-see-these-chemicals-in-a-planets-atmosphere-theres-likely-an-advanced-civilization-there/ #alien #life #technology #civilization #atmosphere #chemosignature #fluorine