Hugh Pickens writes writes "Charles Q. Choi writes that hairspray could one day serve as the sign that aliens have reshaped distant worlds because one group of gases that might be key to terraforming planets are chlorofluorocarbons (CFCs), long-lived non-toxic greenhouse gases that were often used in hairspray and air conditioners, among many other products. "Our hypothesis is that evidence of intelligent life might be evident in a planetary atmosphere," says astrobiologist Mark Claire at the Blue Marble Space Institute of Science. CFCs are entirely artificial, with no known natural process capable of creating them in atmospheres. Detecting signs of these gases on far-off worlds with telescopes might serve as potent evidence that intelligent alien civilizations were the cause, either intentionally as part of terraforming or accidentally via industrial pollution. "An industrialized civilization will be one that will use its planetary resources for fabrication, the soon-to-be-detectable-from-Earth atmospheric byproducts of which could be a tell-tale sign of their activity," says astrobiologist Sanjoy Som. CFCs can be easily recognized in planetary atmospheres because their atmospheric “fingerprint” (i.e. chemical spectra) is very different from natural elements, and are a tell-tale sign that life on the surface has advanced industrial capabilities. Using state-of-the-art computer models of atmospheric chemistry and climate, researchers plan to discover what visible signs CFCs and other artificial byproducts of alien terraforming or industry might have on exoplanet atmospheres. "We are about a decade away of being able to measure detailed compositions of the atmospheres of extrasolar planets," says Som."