I doubt aliens exist on other planets mainly because we were created in God's image and if (I assume) aliens were also created in His image, He would have had to die for them, as well, since Adam and Eve's sin affected ALL of creation. He didn't die twice, which means another planet of aliens would have no hope of salvation because they wouldn't know of Christ's sacrifice.
If they weren't made in His image, then...what? Why? I guess He could have had pleasure in making a planet full of animals, like He started off with here on Earth but it just doesn't seem likely to my mundane little mind.
It'll be interesting to find out someday if He did create life on other planets.
