Nah, it's not Aliens....
The island is Limbo and everyone is dead, no one survived the crash. Kate giving Aaron to his grandmother was a wish. The smoke is judgment day/God/whatever. Once someone has repented or done good, they're history, so that means they have to atone or answer for their sins before they can go away. (That's why so many who seemed to be favorites, like Charley and Ekko, died so soon-they'd repented fully)
OK, I haven't worked out the details....
