A chunk of a comet unexpectedly lit up the night sky over Spain and Portugal — stunning onlookers and alarming European planetary defense officials. A chance video clip posted on X, formerly Twitter, showed a young person’s shocked reaction when the fireball flew overhead and exploded in the Earth’s atmosphere Saturday night. “My God,” the person said in Portuguese. “Damn! What the f–?” The European Space Agency also posted a video clip of the shooting star as it traveled over a “fireball camera” in Cáceres, Spain. The agency said its Planetary Defence Office was “analyzing the size and traje…