I personally don't believe in beings from outer space coming to our planet. What I do believe is that UFO's are nothing more than time machines. Human beings taking tours throughout time just like we take planes now. That is why all pictures of UFO's look alike. It could be the same ship just at different moments of time. I also believe in Ultraterrestrials. People from a multiverse and another dimension if you will that can come into our world rather easily than we can go into theirs. Another theory i have is that in like 1000 years or so our planet will be dying and we will find another habitable planet that we will go to before the earth dies. Around 5000 years after we get there we will be like we are here and want to discover if there is life on other planets and in our travels we will discover earth. Only that Earth never died 5000 years earlier and we will be our own outer space visitors.