Extremophiles challenge everything we thought we knew about the existence of life on Earth. Now, astrobiologists are questioning if some extremophiles are actually aliens living among us. Just who are these incredible creatures, and what can we learn from them?
It never fails: an alien comes to Earth to study us, or spy on us, or hide from other aliens. And he/she always goes native. Just once, I'd like to see an unassimilated alien.