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Jupiter is currently shrinking due to the Kelvin-Helmholtz mechanism. Will this mechanism eventually hold or getting slower? If so, at what size of Jupiter will it stop and why? If not, what will eventually happen to Jupiter?

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  • $\begingroup$ On a related note, Jupiter has a rather large diffuse core. See my answer here for further info. $\endgroup$
    – PM 2Ring
    Jul 27, 2020 at 15:57
  • $\begingroup$ @PM2Ring Revealing, thank you. $\endgroup$
    – Ioannes
    Jul 27, 2020 at 16:23
  • $\begingroup$ Eventually? Heat death, proton decay, entropy... $\endgroup$
    – Ink blot
    Jul 27, 2020 at 17:24

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The rate of shrinkage is decreasing. The reason is that the core of Jupiter is becoming increasingly electron degenerate. Electron degeneracy pressure is almost independent of temperature. Once degeneracy sets in, an object can continue to cool with almost no change in its interior pressure, and hence no radius change. A cosmic example is a white dwarf.

This is not an on/off process, so at no point will you be able to say "Jupiter has now stopped shrinking", but Jupiter's radius will not reduce by more than about 10-20% from what it is now. The ultimate fate of Jupiter is to become a cold, ball of metallic hydrogen (with impurities).

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  • $\begingroup$ By fall of metallic hydrogen, do you mean at 14 Kelvin on the surface or are you speaking more generally. Wouldn't it maintain a helium atmosphere for some time past that? $\endgroup$
    – userLTK
    Jul 27, 2020 at 19:50
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    $\begingroup$ Why would it be at 14k a gazillion years in the future? @userLTK $\endgroup$
    – ProfRob
    Jul 27, 2020 at 21:33
  • $\begingroup$ That's the problem with "ultimate fate" questions, it suggests a ridiculously long time. $\endgroup$
    – userLTK
    Jul 27, 2020 at 22:05
  • $\begingroup$ As I understand it, it will stop shrinking, but very gradually / very slowly or something? $\endgroup$
    – Ioannes
    Jul 28, 2020 at 5:07

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