For all who are interested: <em>Would You Baptize an Extraterrestrial?</em> by Guy Consolmagno (the astronomer in question).
I can't give you much information myself, but I can point you in the direction of some information!
The Vatican has operated its own observatory since the 1700s, and the History section of its wikipedia page gives a bit of an overview. The Vatican Observatory has its own website, including a blog.
Two of the scientists at the Observatory have written a book, Would You Baptize an Extraterrestrial?: . . . and Other Questions from the Astronomers' In-box at the Vatican Observatory, which has been on my wishlist for a long time but I haven't yet bought or read.
One of them also wrote the book Brother Astronomer: Adventures of a Vatican Scientist, which looks like more of an autobiographical work (but still interspersed with information about the Church's past and present relationship with astronomy). In the free preview on Amazon, the introduction cites several significant astronomers who were also Catholic priests:
Christopher Clavius
Francesco Maria Grimaldi
Angelo Secchi
Georges Lemaître
(although I assume that an individual priest/scientist's relationship with astronomy is not necessarily identical to "the Papacy"'s relationship with astronomy)
Also, Christian Theology and Extraterrestrial Intelligent Life is an article from a Catholic theological journal with information about the history of the Church's ideas about intelligent non-human beings, although it doesn't deal at all with the space exploration aspect of alien contact, only with what to think about the aliens once we've found them.