I was just curious....do the gas giant planets (Neptune, Uranus, Jupiter and Saturn) have at least a thin band of oxygen in the atmosphere which would make it possible to live in the sky???? (floating cities)
There is only one planet where gaseous oxygen is found: Earth! And the only reason that Earth has oxygen is because Earth has plants that do photosynthesis. There is no other natural process that we know of that will put significant amounts of oxygen into a planet's atmosphere.
So that is bad news if you'd like to live on another planet in our Solar System. However, it does mean that if we ever find a planet around another star that has oxygen in its atmosphere, we can be fairly confident that there is life of some kind on that planet.
This page was last updated on July 18, 2015.