The movie version of Dune (the one with Sting) was on the other day and a question occured to me. How could a planet like Arakis, a planet with no precipitation whatsoever, maintain an oxygen atmoshere? Oxygen is a very reactive element and it only exists on earth because we have a lot of plant life pumping it out via photosynthesis. Yet Arakis is described as having virtually no water and clearly not much vegetation. So, where does the oxygen come from?