I believe in Aliens, do you?
So an alien invasion from space is a common topic of science fiction writers and in a lot of movies, in some movies the aliens often invade earth to exterminate or enslave humanity. or even to steal the planets resources. 
Yes I love science fiction movies.
They are one of my most favorite movies and show genres. I could watch them for hours. 
Extraterrestrial life
So since the mod 20th century there has been a long and lengthy search for any signs of alien life.