Earth is dotted with humongous, human-made structures that, to an alien eye, may be tell-tale signs of intelligent goings-on.

SALT LAKE CITY — The first thing to know about potential alien invaders is that the U.S. Government no longer classifies them as unidentified flying objects. That sounds too scary. They are classified ...

Europe is quietly positioning itself to attempt one of the most audacious missions in planetary exploration: a dedicated landing on Enceladus to look directly for signs of alien biology. Instead of ...