Edgar Mitchell has said ET if he wanted to could have overrun our planet a long time ago here is way he is wrong. On the issue of being overrun by Aliens, the Proper term from a Biblical perspective is Fallen Angels, Scripture shows us the reason we have not been overun by Fallen Angels is because Our creator ( God ) has been restraining him and his associates in part,,,, when He ( God ) STEPS BACK AT THE END OF THE AGE, During the Tribulation PERIOD THEN HE ( SATAN AND HIS ANGELS ) WILL BE ALLOWED TO OVER RUN THE EARTH FOR A SHORT PERIOD OF TIME. 2nd Thess Chp 2:7 and Rev Chapter 12 and Chp 13 describes the event.