The Church leaves the question of the existence of alien life forms to science. Only if science proved the existence of alien life elsewhere in the universe would the Church then have to determine whether such beings were rational creatures in need of salvation. If the Church determined that there were alien creatures in need of salvation, then the Church would certainly begin evangelization.
In the meantime, it is not wrong for Christians to believe in the possibility of alien life in the universe. However, to actually believe that there definitely are aliens if there is no proof of their existence could be considered “scientific superstition.”
