As science has now proven, the existence of UFOs are nearly impossible.  NASA recently found evidence that a planet (named Kepler 452b) is the nearest Earth-like planet.  In 2017, NASA will be launching a survey satellite in search for more exoplanets, which could also include even more Earth-like planets.  But, Kepler 452b is 1,400 light years away (and other similar earth-like planets are even further away).  So, if you traveled at the speed of light for 1,400 years you would get to Earth – which would make it pretty close to impossible to ever see an alien on our planet (this brings up one of my main gripes with space travel sci-fi movies, where ships are traveling between planets and solar systems – I guess that’s where “hyperspace” comes in handy…).  But, maybe it is possible that a space probe like “New Horizons” could enter at some point into another solar system.  It would have to endure a lot to get there, but, it’s theoretically possible that a space probe (or a piece of it, if it breaks apart) could enter into a solar system and be visible with a telescope (Hubble, etc.).  One of my thoughts about the end of the earth would be that the only things we would have remaining to even know we existed where these space probes.  It’s an interesting thought that maybe one day far into our future, an alien world finds the New Horizons space probe in their solar system.