Do Aliens exist?

[RaiDae]

I was watching a program ages ago, about where it would be possible for life to grow and evolve. The planet would have to be a certain distance away from the sun (not too hot nor too cold), the size of the planet and it's gravitational strength is important, the atmosphere on the planet and it's orbital path (the planet's path isn't necessarily circular and this could induce extreme weather conditions). Those are only a couple of the factors they were talking about (i can't remember the others).
Though the likliehood of a planet satisfying all the necessary requirements is very, very small, there are so many planets out there that I believe there must be a few others like ours. (though they're probably so far away that we'll never know of their existance... )

So, yeah - I believe in aliens