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In various types of stars, one can learn how they evolve differently, depending on factors such as their size and chemistry. Some stars have a short lifetime and others much longer.

But, what is known about the lifetime and evolution of gas giants. Do they just remain stable until some external source, such as the burn out of the sun, disrupts this?

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    $\begingroup$ I sincerely hope you aren't talking about this kind of evolution. $\endgroup$ – Deer Hunter Jun 19 '13 at 6:49
  • $\begingroup$ Think any answer should disambiguate between Jupiter-type and Hot Jupiter-type planets. Hint: the linked wiki article has some refs on evolution :) $\endgroup$ – Deer Hunter Jun 19 '13 at 6:57
  • $\begingroup$ They will contract as they radiate heat (the energy lost comes from the kinetic energy of the gas). This is a very slow process. $\endgroup$ – dmckee --- ex-moderator kitten Jun 19 '13 at 14:22
  • $\begingroup$ Deer Hunter, not that kind of evolution, but that made me a good laugh :) Okey, if they are too near their parent star they will be grilled some layers of gas, and perhaps end up as Chthonian - otherwise just slowly radiating heat and contracting $\endgroup$ – user25675 Jun 19 '13 at 14:59
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Gas giants start big and luminous and get smaller and less luminous.

Their gravitational contraction gives them a luminosity. The virial theorem then demands that they must contract in response if their gas pressure is a function of temperature.

However after evolving for some time, the cores of gas giants become partially and then nearly fully electron degenerate. A degenerate gas can cool whilst maintaining its pressure. As a result the contraction slows and tends towards a cold equilibrium size. Throughout, this evolution the luminosity is approximately proportional to the reciprocal of the age.

The following picture was taken from the review of Fortney et al. (2011, in Exoplanets, edited by S. Seager, Univ. of Arizona Press, p.397), showing the radius evolution for various compositions.

Gas giant evolution from Fortney et al. (2011)

There are many, many details beyond this very rough sketch. The whole field, as you might imagine, is extremely active at the moment, thanks to the discovery of many giant exoplanets. Complications include how do they form; what are the compositions; how do chemical elements separate; how is tidal heating and irradiation felt; what is the high pressure equation of state; what are the cores made of?

Useful recent reviews include

Guillot & Gautier 2014

Baraffe et al. (2014)

Fortney et al. (2011)

Fortney & Nettelmann (2010)

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One process that is happening currently for Jupiter and Saturn is separation of helium out of the mixture of hydrogen and helium.

The prevailing theory is that helium falls like rain from outer to inner regions of these planets.

Saturn is further along in this process since it is smaller and cools faster. This explains the lower observed levels of helium in Saturn's outer atmosphere compare to Jupiter's.

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This is indeed an alternative theory, i first read the above comments and saw a general point of agreement, that is in heat loss and contraction, the General Theory of Stellar Metamorphosis (GTSM) is based on that principle but starts at stars and then stars lose heat, contract and go through phase changes, from plasma to gas, liquid, solid, this means stars and planets could be the same objects just in different stages of evolution. It is a theory that fully encompasses the opening question by user2675, where gas giant evolution is part of this grander theorized process. Jeffrey Wolinski is dong the theory development, this is a link to his starting paper > http://vixra.org/pdf/1205.0107v9.pdf

For the current sciences it is indeed controversial, or not depending on how you look at it, as mainstream science calls gas giants failed stars sometimes, GTSM says they once were stars and are evolving. I think it is good to have different ideas and to keep thinking.

The new Juno mission is exciting in that regard, the blue color at the poles, lots of activity...is Jupiter evolving?

Regards, Daniel

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  • $\begingroup$ Note that vixra isn't a reputable site and none of the articles posted are peer-reviewed, so using that as a reference is highly dubious. $\endgroup$ – Kyle Kanos Jun 10 '17 at 10:38
  • $\begingroup$ Sure, i have no problem with that argument, but to be on topic it seems mainstream science and answers on this page do indicate heat loss and contraction. And Dave PhD said that Saturn is further along in this process... $\endgroup$ – Daniel Archer Jun 10 '17 at 12:14
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Gas giants evolved from being shining stars and will further evolve to become more liquid (uranus, neptune) to water worlds to earth (water/rock) etc. This new theory is called: The General Theory of Stellar Metamorphosis. In this theory stars and planets are the same objects (called Astrons) and they evolve from bright plasma to solid rock, all the while radiating and contracting (with possible expansion phases) and thus evolving. This theory also changes the life paradigm of the Universe since now every shining Astron can become a life hosting world.

Regards, Daniel

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  • $\begingroup$ Welcome to Physics.SE! We usually prefer to deal with mainstream physics here (although alternative published theories are not unwelcome). That said, this theory seems rather contradictory to accepted science. Could you provide references for it? $\endgroup$ – Jim Jun 22 '16 at 13:00

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