Catholic Church says ...

... believing in extraterrestrial life would not contradict Christian thought.

As reported in L'Osservatore Romano, the official newspaper of the Vatican. The article isn't online yet (they appear to be a week behind), but MSNBC has a blurb on the comments by the director of the Vatican Observatory, Rev. Jose Gabriel Funes, SJ*. His thought, as far as the Catholic Church is concerned, all life is the work of the Creator, so it'd be fine. Of course, there is the problem of Jesus' sacrifice for our redemption. If alien life happened to be similar in attitude and behavior (what Christians would term "sinful") and they have no record of ever having religion or a redemption story ... for me, that'd be a big problem. I'm sure it's obvious why.

Of course, Mark Shea, he of Catholic apologist fame, has a much different take on it.

*SJ stands for Society of Jesus, aka Jesuits.