Please, everyone just stop with the silly TV fantasies of aliens flying spacecraft around Earth's atmosphere. While we all hope that other life forms (perhaps microscopic) are present, or even common in the Universe, and we hope that humans can prove the likely existence of life on another planet during the next hundred years with advanced telescopes, the idea that aliens are actively flying around our navy ships, or experimenting on farmers is just silly. Please recall that while there may be as many as 2 trillion galaxies in the Universe (at least the one we are aware of) the nearest spiral galaxy to the Milky Way is Andromeda, which is 2 million light years away. If an advanced society on a planet in Andromeda for some reason decided to visit Earth, they would need to invest massive resources to create a suitable spaceship and to provide fuel to accelerate it to unbelievable speeds. If they could accelerate it to a cruising speed of 50% of light speed, it would take over 4 million light years to arrive at Earth. So it would have launched many years before the first humanoid creature evolved on earth. If they are here now, why don't they stop and say hello? Maybe they are waiting for advice from home base --- oh yes, that message will require 2 million years in each direction, so they will have their orders in 4 million more years. Please read "Rare Earth: Why Complex Life is Uncommon in the Universe". Also, Carl Sagan, also my article on Medium, "Why Aliens will not be Joining Us for Dinner".

There are many possible explanations for "UFO's" but aliens can be ruled out.