The existence of extrasolar planets was, once upon a time, vehemently denied by the church. They even went as far as executing: by burning people alive, anyone that suggested otherwise.
Priests - citing the irrefutable words of their god - taught that everything: absolutely everything, that you saw in the sky revolved around Earth. Our planet - they argued - resided at the center of a clockwork universe fashioned by their immortal geomanter.
Nowadays, of course, we know that this view is utter nonsense. We do not reside at the center of the universe and our solar system is not unique either. As scientists and engineers develop better and better instruments: with which to peer out into the cosmos, more and more extrasolar planets are being discovered all the time.
So yes - there are innumerable star systems: replete with planets, out there awaiting discovery.
The big question now is: is there intelligent life on any of them?