[ZX12R]

However, we do seem to be short of concrete proof that intelligent beings from else where have visited earth.

Not short, there is none whatsoever. Not in all of world history. Not a shred of evidence beyond people's imagination. In fact, there has never been any proof of life anywhere in the universe, besides earth. Not just of intelligent life, but no life of any kind, no matter how simple. Nada, none. Is it possible there is? Of course, but no hint of it has shown up yet.

[Quix]

That’s wholesale inaccurate.

Regrettably it will be proven probably in the next 18 months or so.

[El Gato]

Is it possible there is? Of course, but no hint of it has shown up yet.

Hints? There have been plenty of hints. What looks like fossilized life in meteorite thought to be be from Mars, to cite just one example.

One of Saturn's moons has liquid water(geysers, somewhat like Yellowstone's only larger), CO2, and even a hydrocarbon as complex as propane. CO2 and propane are hints that there might be life there.