Somewhere in the universe, there is a high probably that a planet in a distant solar system has efficient living conditions for organisms to settle on; like that of Earth. The universe appears endless, so there just may be another "Earth" out there that has about the same distance away from a sun. Whether life on such a planet is less or more advanced than that of our own, these extraterrestrial organisms are still classified as "aliens", hence the word extraterrestrial. Overall, I do believe in aliens; we may never set eyes upon such creatures, but nevertheless, I still believe in their existence.