"For most people, any mention of UFOs inevitably conjures up imagery of spaceships from other worlds, and alien abductions. However, the theory that UFOs originate in far-away galaxies is simply that - a theory. In reality, numerous suggestions have been made to explain the UFO presence that has, for decades, fascinated generations of saucer-seekers everywhere. Indeed, the fact of the matter is that, like it or not, we're still very much in the dark when it comes to understanding the true nature of what it is that is amongst us, and which, for so long, has interacted with us. Let's take a look at those theories..."
Those are the opening lines of MY LATEST "MYSTERIOUS UNIVERSE" POST that looks at the various theories offered to explain the UFO phenomenon: aliens, cryptoterrestrials, demons, time-surfers, and more...
PS: No, that is not a UFO above. Just a good old aircraft smoke-ring...
Reference: faces-on-mars.blogspot.com