If alien life is out there, two scientists hope they leave the lights on. To search for advanced extraterrestrial societies, Avi Loeb of Harvard University and Edwin Turner of Princeton University suggest in a new paper, astronomoers should look for city lights on distant planets. The technology already exists to look for Tokyo-sized cities at the edges of Earth’s own solar system, they argued. “Looking for alien cities would be a long shot, but wouldn’t require extra resources,” Loeb, who works at the Harvard-Smithsonian Center for Astrophysics, said in a statement released by the center. “And if we succeed, it would change our perception of our place in the universe.”