Free Astronomy Magazine November-December 2019

27 NOVEMBER-DECEMBER 2019 ASTROBIOLOGY nals towards other planetary systems. Al- though we have been listening to the sky for 60 years now (starting from Frank Drake’s Project Ozma), we have yet to record non- natural signals of clear extraterrestrial ori- gin. An alien civilization that wanted to make itself heard could easily overcome the listening limits of those who are less techno- logically gifted. Accordingly, if we have not yet received messages, it is because the aliens either do not want to communicate with us (which would make the raids in our atmosphere meaningless), or because their signals have not yet reached the Earth due to the enormous distances that separate any planetary civilizations from each other. This second hypothesis is far more relevant – for instance, we ourselves, in 1974, sent a mes- sage to the M13 globular cluster that will reach its destination in about 25,000 years. A handful of civilizations scattered through- out the Milky Way might be separated by tens of thousands of light-years, making the silence that currently surrounds us under- standable. It might even be more strange to not have already received signals sent in the past by civilizations much older than our own and, perhaps, already disappeared. If the average distance between civilizations is so high as to make even the exchange of messages highly unlikely, it goes without IDIOT ! I TOLD YOU WE WERE FLYING TOO LOW! SEE? I TOLD YOU THEY WOULDN ’ T NOTICE US ... ABDUCTING THEM WAS EASY, THEY THINK I ’ M A POK É MON