Anyone who believes in aliens on another planet have their head in the sci-fi movies which means they are delusional. The real aliens are on Earth. The definition of an alien is an unknown species that has not been discovered yet by anyone. I’m quite sure there are undiscovered species in the deep oceans and deep in certain forests. Those are the real aliens and not what you see in sci-fi movies.

Are asking about space aliens or illegal aliens? I guess it doesn't matter. I believe they both exist. 2/17/23

Let's say: I believe that it is extremely likely that primitive forms of extraterrestrial life exist. I mean things like bacteria. I would be very surprised - not unbelieving, just surprised - if no such life exists on planets and moons in our own Solar System. *** Why? Because the panspermia hypothesis makes so very much sense to me. It seems likely to me that ANY planet (in our Galactic Neighborhood, not just in our Solar System) that has liquid water at least frequently is going to have at least primitive life, and what's more: life very much like what we find on Earth, by which I mean: DNA-based, carbon-based, water-based life.

There are something like some order of roughly 10 to the 23 power stars in the universe. To speculate that exactly one planet orbiting exactly one of those stars has matter on it that meets our qualifications of "life" seems ridiculous. But, maybe this is too philosophical, but, I think it doesn't matter, because peeking around the very narrow corner of the universe that we can see, there are extremely few planets that appear to have high enough metalicity and "goldilocks" temperatures to support life as we know it, naturally. If we filter down even more into planets with high enough mass to hold down water on its surface but not so large as to become gas giants, there are even fewer. So, I say it doesn't matter, because the odds of us ever crossing paths at any point in the future is exceedingly low. Now, as far as intelligent life, there is quite notoriously no evidence out there that there are anything similar to humans as advanced as us on any other planet within our observable reach. There are lots of philosophical implications from this, starting with the Fermi Paradox. It could be possible that intelligent life isn't truly that rare, but that it might tend to self-destruct. If you think about the time span between when Earthly humans invented the radio (making us visible to anyone on another planet with similar technology) and when we invented nuclear weapons (capable of destroying our race in an instant), it's only but a moment in the history of our world. These are dark implications for intelligent life in general but maybe not so hopeless for us, at least jsut yet.