Gas giants with athmspheres breathable to us humans.

[Maria Sirona]

Could they exist?

[Beamer]

A breathable atmosphere for humans (obviously) requires around 20% of oxygen. Oxygen is highly reactive and unlikely to exist in those concentrations without some process that constantly replenishes it. If new Oxygen wasn't constantly being generated on Earth it would all just be used up in fires and less violent forms of oxidation and end up as some carbon-oxygen compound or water or various metallic oxides. All in all that means it's unlikely we will ever find any kind of planet - rocky or gaseous - that has breathable air unless that planet already contains oxygen-producing life forms.

Before life, Earth had very little free Oxygen, and the first appearance of oxygen producing life very nearly killed everything on the planet, including the life that produced it, due to the extreme chemical changes in the atmosphere and oceans that it caused. See the "Great Oxidation Event", it's a very interesting episode in Earth's past.

Of course we have no examples of life existing on gas giants, so if that would even be possible is anyone's guess, but it's safe to say that if we ever did find enough oxygen in a gas giant's atmosphere, there'd be something there that might not want to share it with us

 

Edited February 26, 2022 by Beamer
Grammar

[Scotius]

*Raises finger* Ah! A airship-like floating organisms, with organs storing oxygen for metabolic use. Working in a closed-cycle to minimize losses of precious and scarce gas. They might resemble some transparent jellyfish living in symbiosis with algae, following local star to keep them photosynthetizing.

[Beamer]

5 minutes ago, Scotius said:

*Raises finger* Ah! A airship-like floating organisms, with organs storing oxygen for metabolic use. Working in a closed-cycle to minimize losses of precious and scarce gas. They might resemble some transparent jellyfish living in symbiosis with algae, following local star to keep them photosynthetizing.

A Clarke fan as well as a Stan Lee fan I see, excellent But if the airship-like organisms store most of what is already considered a precious and scarce gas, surely there wouldn't be enough free oxygen left to create an atmosphere breathable to humans? Or do you suggest bringing a big box of needles and popping them all?

 

[kerbiloid]

If they are giants, they are full of lighter gases which get oxidized.

But there is a hypothetical probablity close to zero that somewhere in the universe there had been appeared a huge gas ball consisting of oxygen, so you can breathe in its intermediate layer where it's both warm and gaseous.

[Scotius]

Oh no, obviously colonists\explorers would have to live inside those floaters. Nice, stable temperature and humidity, plenty of algae to eat - perfect environment

[jimmymcgoochie]

Gas giants are mostly hydrogen, with a little helium too; oxygen is much denser than those and would naturally sink through the atmosphere, so by the time you reached an altitude with enough oxygen to breathe, the pressure would most likely turn you inside out if you tried. There's also the whole issue of hydrogen plus oxygen plus sparks (from lightning) equals MASSIVE EXPLOSIONS!!!!1!, which on the scale of a gas giant would be unimaginably destructive.