Free Astronomy Magazine November-December 2020

24 ATMOSPHERIC POLLUTION It seems incredible, but in an age when humans communicated remotely using horseback couriers, carrier pigeons, fires and mirrors, the first signals were al- ready being transmitted into space. The Roman, Chinese and Spanish empires unwittingly added traces of their exis- tence to the light reflected from the Earth, and we cannot entirely exclude that those traces have already been no- ticed by an extraterrestrial civilization. The Anthropoc an interstellar by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador NOVEMBER-DECEMBER 2020 I n the next few years, we will be able to analyze the atmospheres of the nearest exoplanets and understand if they contain molecules consistent with the presence of life. Perhaps in those at- mospheres, it will also be possible to recognize “pollutants,” gases not pro- duced by natural processes that could be the result of activities associated with particularly advanced and intelli- gent life forms. Regardless of the com- position of each atmosphere, any ob- servation will provide a snapshot dat- ing back to the moment when the light collected by our instruments left the source. Theoretically, that light, prop- erly analyzed, can tell us if there is an