Complex sentence: Scientific officer Lew Picard declares no life as they know it could exist in that environment--just as a middle-aged alien man appears on the big screen, introducing himself as Mentor of the planet Psychon.
Split into simpler sentences: Scientific officer Lew Picard declares no life as they know it could exist in that environment. Just then, a middle-aged alien man appears on the big screen, introducing himself as Mentor of the planet Psychon.