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I don't know if alien spacecraft have visited Earth or not, but nothing says they would have to be piloted by aliens. If they exist, they could just as easily b

• dwaltrip 9y ago
  That's a good point. Of course, it's possible. I just think it should be the last explanation we consider, after definitively crossing everything else off the list.
• mistersquid 9y ago
  > If they exist, they could just as easily be robotic drones. While perhaps literally included in the group of "robotic drones", one interesting possibility would be craft piloted by highly-developed machine intelligence, what we might call sentient AI.