5. Kitai Is Dreaming The Whole Thing
The Theory: We'll start with the most obvious twist theory, one that is so engrained in the moviegoer's mind that it's practically a joke when its mentioned. But let's think this through: Kitai engages in a life or death quest on the harsh planet of Earth, with creatures that have evolved to kill...US! Ultimately (most likely) he'll be saving the day and reuniting with his father. Or will he?
Supporting Evidence: Judging by how harsh that crash landing was, and the fact that Oxygen masks were required for safe passage, it's a decent bet that this whole thing could be a Jacob's Ladder scenario. A harrowing crash, crossed with lack of oxygen and probably a healthy dose of shock, could lead to Kitai lingering on the knowledge he happens to have of Earth. This fuels his delusion, and in the end we find that he's merely been out of commission the whole adventure, ready to be saved by Cypher. He has a realization that he has what it takes to survive, but he'll need his training to hone those skills, blah blah blah. Roll credits and throw you drink at the screen.