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The best available evidence is that most (probably all) interpretations of UFO's as alien spacecraft are mistaken. People who don't know the sky very well can easily misjudge planets, bright stars, the moon, clouds, comets, meteors, human aircraft, missile tests, bird flocks etc. etc.
Another important fact about possible space travel by aliens is the enormous distances between star systems. It would simply take too long.
We should ask if alien visitation is real. The best answer at this time is no. (Possible, just extremely unlikely)