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Is it possible for gas giants to fuse elements such as hydrogen and helium into heavier elements without collecting it from space?

Obviously, the gas giant cannot perform supernova nucleosynthesis, and perhaps there will be no r- or s- synthesis either. So, any thoughts?

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  • $\begingroup$ It is my understanding that a gas giant - a planet - is per definition not running on fusion and therefore not going to produce heavier elements. $\endgroup$
    – Ghanima
    Oct 20 '15 at 23:16
  • $\begingroup$ Wouldn't this question be better on Astronomy.SE or Physics.SE? $\endgroup$ Oct 20 '15 at 23:21
  • $\begingroup$ @randal'thor - I agree with you there; in fact there have already been questions asked along these lines on both sites. $\endgroup$
    – KeithS
    Oct 20 '15 at 23:59
  • $\begingroup$ No. Until the electrons are stripped away by high temperatures, the nuclei can not get in contact for fusion. $\endgroup$
    – Oldcat
    Oct 21 '15 at 17:36
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Prepare for (possibly) correct but useless answer: yeah, a gas giant will fuse some hydrogen. At any temperature the velocities of particles will follow Maxwell's distribution, so there will always be SOME high velocity ones. Generally, for the PP fusion process, fusion rate increases with the cube of the temperature and the square of the density. So, since the sun's core is about 15,000,000 C, with density about 100 g/cm3 while Jupiter's metallic hydrogen (probably surrounding a rock core) is about 20,000 C and (I found this while reading about metallic hydrogen, not sure enough about the value) around 1 g/cm3.

Thus the fusion rate per cubic centimeter in Jupiter's core is going to be around $10^{-13}$ the rate in the sun's core. The sun's core produces around (ala Wikipedia) about 270 Watts/cubic meter, so Jupiter's core would produce about $3 x 10^{-11}$ watts per cubic meter. That's a whole 30 pico watts per cubic meter. Time to break out the marshmallows!

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  • $\begingroup$ And that's a whopping 20 hydrogen atoms fused per second per cubic meter, if I calculated correctly. $\endgroup$
    – user11599
    Oct 21 '15 at 2:21
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Technically, no.

If it's fusing hydrogen and/or helium then it's performing nuclear fusion and we define that as a star, not a gas-giant.

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  • $\begingroup$ Actually, there's a grey area (technically a brown area) in which masses that don't exhibit full protium fusion and so don't meet the definition of a star, nevertheless display heat production by a low-power fusion process called deuterium combustion (and at the upper end, lithium combustion). These are called "brown dwarfs" and they range from about 13 to about 80 Jupiter masses; below that range a planet's emitted heat is mostly compression heating or re-emission of its star's energy, while above it, the mass is usually dense enough to be a truly fusing red dwarf. $\endgroup$
    – KeithS
    Oct 20 '15 at 23:56
  • $\begingroup$ @KeithS A brown dwarf doesn't fuse hydrogen or helium. So, where is the grey? Heat production was not the question. $\endgroup$
    – Samuel
    Oct 21 '15 at 0:23
  • $\begingroup$ @KeithS Brown dwarfs aren't really a grey area; they're their own class of object. You can't call them gas giants. $\endgroup$
    – HDE 226868
    Oct 21 '15 at 2:20
  • $\begingroup$ There might be planets that are "chuffing" - having there moments of fusion, which would cause the core temperature to go up and the density to go down, causing the conditions needed for fusion to disappear. $\endgroup$ Oct 21 '15 at 2:33
  • $\begingroup$ @HowardMiller If so, the object would be oscillating between brown dwarf and star, so, still not a gas giant. $\endgroup$
    – Samuel
    Oct 21 '15 at 3:47

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