The release of new documents from the Pentagon at the behest of the Trump Administration (which is surely no distraction from the Iranian fiasco) will doubtless excite those certain that we have been visited by aliens.

In as much as grainy, blurred or otherwise unconvincing images of UFO's (more accurately called UAPs - Unidentified Anomalous Phenomena) exist, and they do, there are many more reasons why these are not of alien origin at all.

As best we know, and until it is proven otherwise, the speed of light is the maximum speed limit for our universe. Most interstellar objects are so far away that travel between one star system and another is totally impractical. Even within our own galaxy, which is but one of billions, the distance across is about 150,000 light years. We are about 27,000 light years from the galactic centre alone. Even if an alien civilisation (which has to develop from a primitive society to a technological society far in advance of our own) were to develop the means to travel at a speed approaching the speed of light ( which comes with its own set of very difficult to solve problems), the sheer distances and the time to travel them (thousands, tens of thousands or millions of years) would present an intractable problem. It is just too difficult, and for what return?

That is just one of many reasons why an alien civilisation would reject travelling much beyond their own solar system. I suppose robotic probes travelling over vast time-scales is a possibility, but what are the chances of happening upon the Earth, and why play a strange game of hide and seek? I think if you bought a single ticket in the biggest lottery on the planet, your odds would be vastly better.