Hello all,(adsbygoogle = window.adsbygoogle || []).push({});

Sorry if the question sounds idiotic, but this morning I was watching a program on Jupiter and then I couldn't wrap my head around this. Say a slowly changing gas planet that is cold enough to have very little convection, and that by assumption does not lose its mass to space. Then draw some radius around a fixed mass M1 around it center (say 1 trillion tons); that will have a volume V which is very slowly changing. Then I know that pV = nRT. Now consider the rest of the gas outside that volume; that that's M2 = 1 quatrillion tons.

Now it gets very complicated for me, and here's the thinking. The planet will always lose heat through radiation; so let 1 trillion years pass. Whatever T it started with, in the long term T must end up being very small (for the reason that a higher T will lead to more heat loss due to radiation).

As R is constant and under my definition n is constant too, then pV is going to be very small. But there is a huge weight of the fixed mass M2 pushing down through gravity on my volume. So p cannot be very small. Therefore, V must be very small, and given that the radius of the volume is very small and the mass M2 is fixed, then p must be large.

As T is very small and p is large, then the core of a large enough gas planet must at some point freeze or liquefy. Therefore, above some size it should be impossible for a gas planet to remain gaseous forever. But that sounds preposterous, because it means that in the long term there would be no more large, completely gaseous planets, for thermodynamics alone...

I appreciate any insight where may train of thought has gone off tracks on that.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# B Are gaseous planets unstable?

Have something to add?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**