Life probably exists in space, simply because it's totally possible for a planet similar to earth to exist somewhere else in the universe. Will they be able to visit us? Nobody knows. Will we, the regular people, ever find out the truth? Probably, when the time comes. I find no reason to speculate about this. If they can reach our planet, they have better technology than us. If they don't want to be seen, we will not see them. If they want to see us, they'll make sure we see them.