Pollution could be a sign of alien civilization, study finds
Many compounds that can possibly be found in the atmospheres in other planets can often only be made through industry.
The planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our Solar System, is seen in an undated artist's impression released by the European Southern Observatory August 24, 2016.(photo credit: ESO/M. KORNMESSER/HANDOUT VIA REUTERS)
