There’s no mainstream scientific proof but the odds are great that they must exist. We in the paranormal investigative community have certainly had dealings with aliens. The Universe is so beyond vast that it would simply be fake if no other intelligent life existed. God clearly made everything look naturally created in our reality so we can assume he extended that to life on other worlds. We know microbial life exists on other planets such as Mars but so far we haven’t made contact with an advanced species. Although rumors indicate that we have been visited numerous times throughout our history. That includes recent times which include reports of government collusion with aliens, and numerous incidents of humans being abducted for nefarious experiments.
Since the Universe seems to follow the same process for the formation of stars, planets, planetary atmospheres, water formation, etc. it’s safe to assume that the process would eventually lead to life evolving elsewhere under the right conditions which include a planets distance from a star. The odds are simply too astronomical that intelligent life evolving on Earth is merely a fluke.