Scientists explore possibilities of extra-terrestrial life in 100 galaxies of the visible universe. This feature length film is an "Encyclopedia Galactica" of extraterrestrial life forms, and an investigation into the latest scientific understanding of life beyond planet Earth. ALIENS: THE DEFINITIVE GUIDE showcases the extraordinary scientists who are currently grappling with extraordinary questions about alien life including: what will aliens look like? How will they sound and communicate, and will they come in peace?