What unique fear do martians or other aliens represent as opposed to zombies vampires and other types of monsters

martians or other types of aliens represent a unique fear as opposed to zombies. vampires and other types of monsters.   in most sci-fi stories, aliens come from other worlds and have different or more advanced technology.   abductions and experimentation on human bodies that involve these technologies, or the use of these technologies against human beings and the use of unknown "powers", are a type of fear that's different from that of other types of monsters.  

what makes a hero is someone who tries and acres and then to save people and it’s not their jobs to save them just a normal person that has no experts of saving people would jump in to action without it twice about doing it. me that’s the defection of a hero!