From this press release:

The truth is out there. With increasing numbers of people believing not only in the possibility of intelligent life on other planets, but even claiming encounters with aliens, it is not surprising that the Catholic Church is beginning to explore what effect the discovery of sentient ETs might have on Christian theology.

Apparently, this is a pressing problem for the Holy See.

Would humans recognise intelligent life if we saw it?

I’m not optimistic.  But let’s return to the topic of aliens.

Could we communicate with it? Should we even try?

No.  I say we ignore it.  Play "hard to get".

Is Original Sin something that affects all intelligent beings?

The doctrine of original sin holds that every person born into the world is tainted by the wrong-doing of the first ancestors (Adam & Eve), confused because they were deceived, corrupted because they were ruined, fearful of death because they were punished, etc.; so that, all of humanity is ethically debilitated, and powerless to rehabilitate themselves, unless rescued by God.

So I’m going to say "no".

Is Jesus Christ’s redemption valid for intelligent beings throughout the universe? …or would other worlds have their own version of Jesus?

No.  See above.  (Although, I have a funny feeling that the Catholic Church might suggest otherwise).

Would the Church send missionaries to ET planets?

You betcha.  And I’m sure those missionaries will be well-received.  In fact, why wait?  Send those missionaries to other planets right now, I say.

Could you baptize an alien? …or for that matter, could you ordain an alien?

What if the alien bursts into flames when it is anointed with holy water?  What if the alien has no neck, and therefore cannot wear a "collar"?  If the alien has five mouths, does it get five communion wafers, or is one sufficient?