International Space Station commander Leroy Chiao believes aliens exist.
Chiao revealed he is fascinated by the possibility that life exists on another planet and he says that given the size of the universe, it's difficult to believe that humans are alone.
He told the Science Channel: ''I think the big mystery to me is finding other life in the universe.
''Because I believe that there is life out there - in fact, I believe there is a lot of life out in the universe.
''The universe is infinite. It would be the height of arrogance to think that we here on the earth in this basically infinite universe.''