NASA's Unexplained Files Season 6 Episode 2 Aliens vs. Stalin at Area 51 ( Air Date 2019-04-18 ) Genre Documentary, Talk, Mystery category. Overview "When a former Area 51 insider alleges that the Roswell UFO incident was a nefarious Soviet conspiracy masterminded by Stalin, experts investigate if it was indeed an enemy plot against America -- or if the confession is just another cover-up.".