Is it true a planets atmosphere can exist beyond its diameter?

I saw an article about how the minimum mass to retain water is 2.7 Earths mass. It said if the planet moved in the inner habitable zone the atmosphere expands and can be multiple times the planets diameter. It would be like a planet smaller than Mercury having an atmosphere 2 times its diameter. Wouldn’t that be seen as a mini gas giant. Could one technically breath at 20 miles up?

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  • 4 weeks ago
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    Mercury and our Moon which is bigger don't have enough Volume or Mass to have any substantial Atmosphere never mind water

     it would Evaporate

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  • 4 weeks ago

    Unless you read without your glasses, that article is wrong.  Earth has 1 "Earths mass" and retains water.

    Never heard of an atmosphere "multiple times the planets diameter".  It is usually just a thin covering.

    Without special training, a person will pass out in a few seconds at 30,000 feet (8 Km) high.  That is how Air Force personnel are trained to put on masks in aircraft.

    To be exposed at 60,000 feet to unpressurized atmosphere will result in death from the bends.  Blood at body temperature will boil at that attitude.  At 20 miles or over 100,000 feet altitude, that is almost like space.  Only a couple dozen balloonists and some pilots have been that high.  And they had pressure cabins or suits and oxygen.  Nothing much to breathe.

    Same goes for Mars.  Its air density at surface is like being 20 miles above Earth.  No oxygen at all, just carbon dioxide.

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