Could oxygen exist in abundance on a desert planet. How about gas giants

[Dartz]

While I was watching Star Wars the other day, when they were on Tatooine, I got to thinking, would oxygen be able to exist in an abundance on such a planet?

From my understanding, Earth got its' oxygen through photosynthesis by plants and bacteria. So, would it be impossible for a planet like Tatooine, or Hoth, to form an oxygen atmosphere, to a level humans could breath?

On a similar note, the planet Bespin, the gas giant with Bespin, also seems to have a breathable atmosphere.

[smjjames]

Well, both planets have life forms of some kind, so its entirely possible for them to accquire an oxygen atmosphere.

For a terrestrial (Earth size or Super-Earths) worlds, life is required to have a significant oxygen atmosphere.

Regarding gas giants, it would depend on the composition of the protostellar disk and how much of the oxygen isn't locked up as water or other compounds. A gas giant with some free oxygen in its atmosphere? Maybe, but in significant amounts to the point where its breathable by humans? Most likely not without some proccess that is continuously producing free oxygen. Although they weren't shown in the movies, Bespin is supposed to have life forms as well (Tibanna gas is actually produced by giant blimp-jellyfish).

The problem is that oxygen is reactive, it'll bond with other atoms the first chance it gets, so any free oxygen won't stay that way for very long before it reacts with something. Therefore, for a significant amount to stay in the atmosphere, something needs to be producing that.

[Desacabose]

In theory, yes.Nothing truly prevents a a desert planet from having Oxygen.However they would require some way to form it, say plants as on Earth. Oxygen can not stay in the same state very long.Both of the planets you mentioned have life so, yes.But a desert planet with no life it is exceedingly likely that Oxygen would be at a minimum,if any. As for Gas gaints....that depend entirely on the composition of it's proto-disk, so...eh...possible though even if some type of being existed in gas giants.They would be very different from human life.And even if trace amounts of Oxygen manage to stay in a gas giant it wouldn't be enough for human life without impossible Terra-forming(Also humans would be crushed)
Example:Jupiter is about 82 % hydrogen,18 % helium and traces of nearly all other elements.

[vh]

Most of oxygen (on earth) is formed by organic processes. In the universe, probably supernovas are the main source of oxygen.

Also, on a similar but unrelated topic, apparently, hydrogen is so rare in rocky planet's atmosphere because they move fast enough and diffuse out of the atmosphere even with gravity.

[karakris]

Oxygen is indeed produced by Biological Processes - meaning a Planet which has Evolved Life.
This is produced from Gas like CO2 which was originally produced by Volcanic Action.

Riiight - a nearby Star Goes Nova - Life is extinguished, perhaps dying eventually - and you get a Desert Planet.

BUT - there would be more Volcanic Gases.

However - Extinguished Life on a PLanet which has become effectively Geologically Inactive.
That is - Tectonic Activity down to Zero, No Volcanoes, Hot but cooling Mantle, Very Hot but cooling Core.