Aliens Have Pollution

So what else are they hatching? You'd think they'd of discovered advanced recycling.

How to Find Aliens? Look for Pollution on Other Planets Discover Magazine
Scientists have proposed what seems like an obvious solution to finding life on other planets—look for pollution similar to that found on Earth. Light or air pollution would be a dead giveaway to life on another planet, according to a study to appear in the journal Astrobiology.