I'm always puzzled by the statement, whether from fundamentalists or atheists, that the Bible's message is not compatible with life on other planets. The two subjects simply have nothing to do with each other. So if anyone's expecting Judeo-Christianity to come tumbling down when someone finds a microbe on Mars (not that I expect this to happen), they'll be disappointed. Now, on the other hand, if we find intelligent life, and they're saying, "Who is this God you keep talking about? We've never heard of God", that would be problematic.
However, it's likely that, if there are intelligent minds on other planets, they too developed religion as an answer to their early questions and fears. Even if they've since moved entirely past religion (and we can't automatically assume that any amount of technological advancement will remove the tendency to believe in God), if they once believed in God, then this will be taken as a sign that they have gone entirely apostate as a race, and need to be reconciled with God. Interplanetary missionaries will be promptly dispatched from all major churches to help them come back to their senses.
If it turns out that they have a concept of God, but no record of a claimed Messiah in their history, this can simply be taken to mean that God has not yet delivered their Messiah, although admittedly this will give some Christians pause as they wonder why God would allow this race to advance so far, and contact other planets, while not being reconciled with God yet. Self-proclaimed Messiahs will likely spring up at this point, claiming to be mediators between the aliens and God. And so on and so forth.