I have written about this (thanks David for mentioning). Clive, in my article “Is it a bird? Is it a plane? It’s a bird, Sergey…” I have specified the reasons for my “narrow-minded” rejection of the theory that some of the sightings reported are indeed of space ships or other flying objects that originate from other star systems. As with everything that does not contain a blatant logical fallacy, the possibility that they might be extraterrestrial objects cannot be completely refuted. I reject the theory on the basis of probability, and give four reasons why we must reasonably assume that we have never been visited.