Latest info from Kepler suggests about 2 billion habitable planets in our galaxy ... and I guess that there's a couple or three more galaxies out there
... maybe there are a few of our neighbours dropping in for a look see. They don't seem to hang around tho'. Maybe the original scouting ship landed in Yorkshire, assumed that was typical of Earth, and gave our planet less than rave reviews as a tourist destination.
Two billion planets in our galaxy may be suitable for life | Science | theguardian.com