What’s the Catholic position on the existence of extra-terrestrial life?

There isn’t an official Catholic position on the existence of extra-terrestrial life because whether life exists on other planets is a scientific, not a theological question. However, if life on other planets is ever discovered, there are theological questions which can be considered. In his novel Perelandra, C.S. Lewis speculated about the possibility of a fallen race much like humanity influencing un-fallen extra-terrestrials. We were affected by the fallen angel Satan. There’s nothing in the Bible to say humanity couldn’t have a similar effect on another extra-terrestrial race. Humanity might also play a part in the redemption of another race--a role in their salvation history. The good angels played an important part in ours. (Matthew 28:2-5; Acts 7:38, 53).
 
It’s possible God has set up multiple worlds, some fallen, some not, but there’s not the slightest scientific evidence God has. A few scientists, pandering to the tabloids, claim extra-terrestrials must exist, based on the mathematical likelihood of other stars having planets, but their theories are scoffed at by nearly the entire scientific community. The argument often runs like this: If some of those planets have atmospheres like Earth’s and if some of those Earth-like planets spontaneously generate amino acids and if some of those amino acids results in higher life-forms, then intelligent life exists on other worlds. You’ll note a lot of “ifs” there.
 
To insist there must be intelligent life elsewhere in the universe is to overstate the case. It’s also theologically irrelevant because the central tenets of Christianity remain intact with or without little green men.
 
However, God is the God of the universe, the God of things seen and unseen. Jesus Christ’s redemptive act on the cross and glorious resurrection is not bound by our time and space. Therefore, it is important that we remain open to the possibility that an all knowing, all loving and generous God may have created more than we could ever imagine!