Aliens aren’t gods. If they exist, they’re life forms in some capacity similar to us. We know life can exist, since we do, so it stands to reason that since life exists on earth that it could exist somewhere else. Nothing about aliens conceptually requires anything that we don’t already have a scientific method for studying.
Now compare that to gods. Do we have visible or verifiable gods on earth? No, we have a lot of conflicting claims about gods from various belief systems. If we don’t have supernatural creatures/entities on earth, then there’s no reason to believe they exist anywhere else. Whether that’s Pluto or five galaxies away.