Alien to the Bible
"The questions of life's origins and of whether life exists elsewhere in the universe are very suitable and deserve serious consideration," said the Rev. Jose Gabriel Funes, an astronomer and director of the Vatican Observatory. Vatican Seeks Signs of Alien Life
I think that about sums up the issue I have with the Catholic Church. Forget the Bible, we don't need to use it as a source of knowledge! The Vatican accepts Evolution without even thinking about the theological ramifications of the decision, far less looking at the many scientific issues with the theory of Evolution. With this fool-hearted acceptance of Evolution as Truth (and the Biblical Creation account as a lie), it is no surprise that they'd expect that life could have "developed" (their word) elsewhere in the Universe.
So what issue is it if life did develop elsewhere? First, God created everything within 6 days. (Genesis 1, Exodus 20:11, John 1:3) This means that if aliens existed on another planet, they had to have been created within these 6 days. Nowhere in the Creation account does it mention God creating life elsewhere, only on Earth is life created. In fact, the reason for the stars is "for signs, and for seasons, and for days, and years," (Genesis 1:14) not for life. Plus, the stars where made for us.
Then God blessed them, and God said to them, “Be fruitful and multiply; fill the earth and subdue it; have dominion over the fish of the sea, over the birds of the air, and over every living thing that moves on the earth.” Genesis 1:28
We are to have dominion, sovereignty, control over all of Creation. It was made for us, and handed over to us in this first covenant between God and Man. So this means that if life exists on another planet, it is ours to control, subdue, and govern! The only "intelligent", or sentient, life in the whole Universe is us!
So lets move past this, and say that for some reason, despite what the Word of God says, life does, in fact, exist elsewhere in the Universe. What conclusions can we draw about this creation? All life was made good (pure, perfect, without flaw) in the beginning. (Genesis 1:31) So this means that the aliens had to have started out good. Man fell to sin, and because of this, God brought curse upon all of Creation in death, decay, and pain. (Genesis 3:17-19, Romans 5:12) So, from this, the perfection of the alien world would have been tarnished by Adam and Eve's sin. Now, if these aliens somehow maintained righteousness, we don't have much of a problem, but we must assume that the aliens, like man, fell into sin. (Romans 3:23)
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. John 3:16
But, through mercy and grace, Jesus came and died for all, right? Wrong! He died for the blood of Adam! His blood was the blood of humanity, and just as sin entered the world through one man, salvation and life can be had through the righteousness of one man! (Romans 17-18) So if aliens exist, and if aliens are fallen, Christ's Blood Redemption was not for them, only for us.
So what we see in the Bible is that the entirety of Creation, from the farthest reaches of the Universe to the smallest organism on Earth, was created for us (Genesis 1:28), our fall from righteousness into sin and filth cursed all of Creation (Genesis 3:17-19, Romans 5:12), God brought salvation to the bloodline of Adam through the death of Jesus Christ (John 3:16, Romans 17-18), and there would be no means of redemption for aliens (if any existed). Biblically speaking, though, there is no reason to assume that life exists elsewhere, because God told us what He created, and all of that happened here on Earth. The only reason to assume life exists elsewhere is a belief in a natural, without the hand of God, origin of life, which is not Biblical at all. The Catholic Church, among many others, tries to append God to Evolution and throw out the Creation account, so aliens is a logical conclusion for them.