# What will happen to atmospheres of very large planets?

Our earth can hold our atmosphere whereas Mars cannot. So the atmosphere retention mass must be between the masses of Mars and Earth, but if mass is to be considered then can an iron ball having the same mass of the earth hold an atmosphere of it's own?

Also since larger planets can hold larger atmospheres, If a planet like Jupiter was like the earth in composition and the atmosphere contained gases in the same ratio as here on earth, will it result in the atmosphere being modified to suit the conditions of higher pressure and gravity of the planet?

What kind of atmospheric changes could be expected?

Can a very large planet result in the liquefaction of gases(I know that planet size is not the prerequisites for the presence of liquified gases but if), if it does, can it be due to gravity alone?

• A basic hint for the first question: think about the escape velocity of the body. Escape velocity is given by $$\sqrt{\dfrac{2GM}{R}},$$ where G is the gravitational constant, M is the mass of the body, and R is the radius of the body. May 14, 2019 at 10:57
• Regarding the second and the third question: (assuming that you are thinking about a planet as big as Jupiter which is a terrestrial planet and not a gas giant), the gravity would be so large that: 1)The atmosphere would be much larger; 2) the gases in the lower layers of the atmosphere would be under high pressure and thus would be liquefied or maybe even solidified. So yeah, the atmosphere would be "modified" and yes, this leads to liquefaction of gases. But I'm not very sure where gravity is the only factor in play here or not. May 14, 2019 at 11:12
• This depends strongly on what you consider, in terms of the amount of gas present, to constitute an "atmosphere". If you get really, really strict about it, even the Moon, technically, has an "atmosphere". May 14, 2019 at 11:29
• Possible duplicate of What is the critical mass of a planet to have an atmosphere like Earth's? May 14, 2019 at 11:33
• That's why I wrote if the planet considered was same in composition of earth in both the planet's makeup and with regards to atmosphere in the sense the giant planet also has 72% Nitrogen etc. May 14, 2019 at 11:41