So many people believe in aliens and UFOs. Although scientists dismiss these beliefs as not representing real physical phenomena, astronomer Chris Impey says the existence of intelligent aliens is scientifically plausible. Author: Chris Impey (University Distinguished Professor of Astronomy, ...

How was Wernher von Braun so far ahead of everyone when it came to rocketry? See theories in this scene from "NASA's Secret Agenda." Subscribe for more from Ancient Aliens and other great HISTORY shows: http://histv.co/SubscribeHistoryYT Find out more about the show and watch full episodes on ...