The church has no stance on the topic. We are left to believe what we choose. Considering the vastness of space, we will likely not know until/if we are fortunate enough to enter the Gates of Heaven.
I personally believe there is no other intelligent life out there. The arguments from probability due to the huge size of the universe are not convincing.
There have been a couple of Christian novelists who have speculated on how it would happen with science fiction novels. C.S. Lewis wrote his space trilogy, and the first two books describe life on Mars and Venus respectively. Very interesting take: with Mars the people never fell to sin. With Venus, he actually describes the temptation of their “Adam” and “Eve”.
A few years back I read the book “Voyage to Alpha Centuri” by Catholic author Michael O’Brien. That was a really interesting take on the subject. In the near future (I believe it was around the year 2100), we developed the means of travelling in a space ship at 1/2 light speed, and sent a large space ship to Alpha Centauri. The trip took 10 years, IIRC. The found archeological evidence of a civilization on a planet in that system. It turned out that they were from earth. Before the flood, the earth had been taken over by the devil. The devil, when realizing God was going to destroy the earth with the flood, gave people instructions on constructing a space ship and saved a remnant of his people by sending them to Alpha Centauri. They started a civilization that was dominated by worship of the devil, human sacrifice, etc. They were wiped out by plague 2100 years before arrival (ie at the time of Christ). Believe it or not, I have not spoiled that much of the book. A little, but I left enough out to where it is still certainly worth reading.