You ask if aliens exists in the universe, however you should know not all aliens need be intelligent. Most of them are probably germs. Just look at Earth. Not all creatures here are human! Most of them are insects, plankton, germs, fish, mammals and birds.
The law of probability suggests that there exists alien biodiversity somewhere else because the universe is pretty big. However, there is no proof or hard evidence that even an alien microbe exists at present. Maybe we’ll discover something growing on Titan one day.
Perhaps we’ll even discover another intelligent self-aware life form out there.
At present, however, nobody knows.