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 7 64 SP1 Gigabyte 970A DS3P FX AMD FX6300 Vishera 3.5 Ghz GeForce 750 Ti 2Gb Twin Frozr (donated because my Radeon 4GB card burned out, twice) 8Gb Kingston 1600Mhz Logitech G930 (fell apart into pieces like a stale cracker) now using a cheap substitute with bad connectors