Pandoran atmosphere hypotheses.

['upxare]

Diameter = 11447kms (6868 miles)
Mass = 0.72 Earth (4.32 x 10^24kg)
Gravity = 0.8 Earth (7.84m/s)

Interesthing. Didnt know that. And amazing, since Pandora's size comes at 89,73% of earth's, its mass is only 72% of earth's. Is there any explanation?
What confuses me: Since Pandora has significantly less mass than earth, how can it hold such a dense athmosphere, increasing the gravity "back" to 80% of earth's?
ANd last but not least, how could there ever be 18% CO2 in the athmosphere?? Lets not push it to the unobtanium there..

[Mongo]

One word: Venus.

Diameter = 12103.6 km = 0.9488 Earth
Mass = 4.868 x 10^24 kg = 0.8148 Earth
Gravity = 0.904 Earth

Yet its dense atmosphere is 97% CO2, with a total surface pressure of about 93 times that on Earth.

Apparently, the tidal flexing of Pandora due to the other large moons results in quite high levels of volcanism, hence the high atmospheric CO2 and H2S levels.

[Human No More]

Interesthing. Didnt know that. And amazing, since Pandora's size comes at 89,73% of earth's, its mass is only 72% of earth's. Is there any explanation?
What confuses me: Since Pandora has significantly less mass than earth, how can it hold such a dense athmosphere, increasing the gravity "back" to 80% of earth's?
ANd last but not least, how could there ever be 18% CO2 in the athmosphere?? Lets not push it to the unobtanium there..

A significant amount of the atmosphere is Xenon.
Some planets have far more than 18% CO2, it's not impossible.
As for density, it is likely different from a different mineral composition. Not all planets have the same density. Earth is 5.5g/cm3, while Mars is 3.94 and the moon is 3.344. Saturn is 0.7 (so it would float, lol)