Stepping Up the Search for ET

Atmospheric pollution may not be among mankind's proudest achievements, but it's an incontrovertible sign that we are here. Could something similar help us find civilizations on other planets? That's the premise behind one of several recently announced new approaches to the search for extraterrestrial intelligence. Pollutants like Earth's in the atmospheres of other worlds could serve as biosignatures indicating the presence of advanced civilizations there, said a team of researchers at the Harvard-Smithsonian Center for Astrophysics.