Although no conclusive evidence of aliens has been found, some scientists believe it is likely that some kind of extraterrestrial life does exist somewhere in the universe. However, the stories of alien encounters on Earth are most likely false.
UFO sightings can usually be explained by natural phenomena or misidentified aircraft. According to the Harvard University Gazette, alien encounters or abduction stories are believed to be caused by several psychological mechanisms, including sleep paralysis and false memories. Astronomers have identified approximately 40 billion planets in the known universe that may be able to support life, but that does not mean that they currently do. Even if alien life does exist, it may be in the form of bacteria or other unintelligent life.