I think it's not inconceivable that they are alien but not "manned", we've often thought that the distance is far to great to even the nearest possible habitable exo-planet and perhaps it is for humans but not for some robotic machine of extra terrestrial technology. I mean look at all the things we are exploring now in terms of robotics and energy development; a plane that creates its own wind? a robotic worm that projects it's form from within? we've only scratched the surface of what is possible ourselves, we can't just dismiss the possibility that we really aren't alone.
Windows 10 Pro Gigabyte 970A DS3P FX AMD FX6300 Vishera 3.5 Ghz ASUS STRIX GeForce GTX 970 Overclocked 4 GB DDR5 16Gb Patriot Viper 3 RAM DDR3 1866Mhz Onikuma Gaming Headset (has annoying blue lights I don't use)