Gas Giant Cores

[ajtribick]

Couple of questions about the interiors of gas giant planets.

Does Jupiter have a degenerate core, and roughly what mass does core degeneracy begin?

Is it true that Uranus and Neptune have no liquid hydrogen, and at roughly what mass does a gas giant begin to contain liquid hydrogen?

[Bob Hegwood]

Is it true that Uranus and Neptune have no liquid hydrogen, and at roughly what mass does a gas giant begin to contain liquid hydrogen?

Mr. Chaos,

No LMH (Liquid Metallic Hydrogen) for sure on Neptune, don't remember for Uranus. Check
the NinePlanets website for more info and links that will detail the cores.

Hope that helps, Bob

[eburacum45]

From this link
http://cosmos.colorado.edu/stem/courses ... 5/l5S6.htm
it says that the core of Jupiter is degenerate, i.e. compressed more than normal matter so that the mutual repulsion of the electrons and protons is partly overcome;

this compression has a factor of 2 in Jupiter's core, and even occurs in Earth's core with a factor of 10%; so I would say that yes; all major planets are large enough to overcome degeneracy pressure to some extent.

As to what the cores of Jupiter, Neptune, et al are made of; to find out the true situation I think a few more probes need to be sent out; when the money will be available I wouldn't like to guess.

I have been assuming for my own fictional planets that solid cores exist in most gas giants; iron cores, rocky cores, icy cores, sometimes overlain by liquid hydrogen or even water in some cases.

[granthutchison]

Is it true that Uranus and Neptune have no liquid hydrogen, and at roughly what mass does a gas giant begin to contain liquid hydrogen?

Depends on your definition of "liquid". The pressure inside both planets is too low to form liquid metallic hydrogen, as Bob reports. Also, since their interior temperatures are above the critical point for hydrogen, hydrogen doesn't exhibit any distinction between the liquid and gas phases - the density simply increases slowly with depth, with no abrupt change to indicate the onset of a liquid phase. But deep within both these bodies you'll find hydrogen behaving more like a liquid than a gas.

... it says that the core of Jupiter is degenerate, i.e. compressed more than normal matter so that the mutual repulsion of the electrons and protons is partly overcome

But, the mere fact that degeneracy pressure is partly overcome doesn't imply that degenerate matter has been formed. To qualify as degenerate matter, a substance must be so compressed that the Pauli exclusion principle is the dominant component to its pressure - see, for instance, the Wikepedia article on the topic. This usually implies at least white dwarf densities, in which case gas giants just don't get big enough.
Interestingly, though, the same article gives metallic hydrogen as an example of degenerate matter (since it's effectively a sea of protons and electrons), but I'm not sure if that's what chaos syndrome had in mind.

Grant

[maaf]

Personally I would like to classify ordinary metals as being a kind of "degenerate matter", so we could say that we can see degenerate matter everyday (See my post "Degenerate matter and metals") and also highlight some similarities that exists between white dwarf material and metals, but I don't think I can screw up with definitions at free will, (unless I want to create confusion). If metals were classified as degenerate matter, we could say that even Earth has a degenerate core! Anyway, if there's an official definition for "degenerate matter", whatsoever it is, I will stick with it.

Best regards.
Marcio
The one who likes to discuss about definitions.

[eburacum45]

Obviously I was wrong to state that the centre of gas giants are degenerate to some extent;
the useful definition of degenerate matter seems to be that matter in which the Pauli exclusion principle is the dominant component of the internal pressure.

I found it interesting for worldbuilding purposes, that the solid cores of planets are compressed; this means that when gas giants lose their overlay of atmosphere the core expands; either in the case of a chthonian planet like Sisyphos or an artificially depleted world like Pluton the core will expand and change state quite considerably.

[Evil Dr Ganymede]

I found it interesting for worldbuilding purposes, that the solid cores of planets are compressed; this means that when gas giants lose their overlay of atmosphere the core expands; either in the case of a chthonian planet like Sisyphos or an artificially depleted world like Pluton the core will expand and change state quite considerably.

I don't know how likely this is, but I've been under the impression that if you strip a gas giant of its outer layers then it practically "explodes" as the pressure is reduced on the interior and the compressed phases of hydrogen change into uncompressed phases - this causes the giant to rapidly increase in volume and encourages more gas to escape. Could that happen?

I wonder about the phase changes in the ice or minerals in an icy or rocky core too if it's exposed. Would that release heat at all? If so, could it melt the core?

[eburacum45]

Yes, in most cases that will probably happen until you are left with a hot solid or perhaps molten core; some worlds might have only a very small solid core, especially if the disk instability theory of gas giant formation is correct (even then a gas giant will engulf a certain amount of asteroid material).

I think gas giants will prove to have a much wider range of compositions than the examples in our solar system- some will be giant, icy water worlds perhaps with vast ice cores and relatively thin atmospheres; Uranus and Neptune might have large ice cores, and this is the sort of world that my fictional ice core world Pluton once resembled.

How thick is Neptune's atmosphere, and if it was removed, to what extent would the icy core (if any) melt due to internal pressure release?

This cross-section of Neptune is a fairly recent idea of the interior of that planet, taken from here
http://www.solarviews.com/cap/nep/nepint.htm

[maaf]

eburacum45 wrote:

Obviously I was wrong to state that the centre of gas giants are degenerate to some extent;
the useful definition of degenerate matter seems to be that matter in which the Pauli exclusion principle is the dominant component of the internal pressure.

Perhaps not, unless it contradicts an official definition for "degenerate matter", if any. According to Wikipedia, although ordinary matter is not usually regarded as being "degenerate matter", sometimes is useful to treat, in metals, the conduction electrons alone as a degenerate, free electron gas.

From Wikipedia:

Exotic examples of degenerate matter include neutronium, strange matter, metallic hydrogen and white dwarf matter. Degeneracy pressure contributes to the pressure of conventional solids, but these are not usually considered to be degenerate matter as a significant contribution to their pressure is provided by the interplay between the electrical repulsion of atomic nuclei and the screening of nuclei from each other by electrons allocated among the quantum states determined by the nuclear electrical potentials. In metals it is useful to treat the conduction electrons alone as a degenerate, free electron gas while the majority of the electrons are regarded as occupying bound quantum states. This contrasts with the case of the degenerate matter that forms the body of a white dwarf where all the electrons would be treated as occupying free particle momentum states.

Besides that, isn't the same Pauli exclusion principle that prevents atoms from collapsing? So what should be the distinction between non-degenerate matter and degenerate matter?

In this link, the author states that even small planets, like Earth are supported by degeneracy pressure.

http://cosmos.colorado.edu/stem/courses ... 5/l5S6.htm

Perhaps both me and the author of the page above are wrong. Perhaps not.

Perhaps the best thing I should do is to ask to some scientist that works with condensed matter at extreme pressures or with matter found inside white dwarfs if is there any official definition for "degenerate matter". If he/she answers no, then I could ask if it's appropriate to classify ordinary metals as a kind of "degenerate matter of electrons" or not. Unfortunately I'm not with enough time to write to someone about this subject and to study more about it. But surely a scientist that studies the interior of white dwarfs would probably know much more about the similarities and differences between ordinary metals and densimetals than me. (I dubbed "white dwarf material" densimetal).

Unhapply I'm very busy these days, so I'll have to leave the discussion about "degenerate matter" for the future.

Sorry if I wrote to much about this subject, but this subject became kind of an obsession for me.

_______________________________________________________

A last word before I go:

I'll break this post, it's becoming too large...

[Evil Dr Ganymede]

I think gas giants will prove to have a much wider range of compositions than the examples in our solar system- some will be giant, icy water worlds perhaps with vast ice cores and relatively thin atmospheres; Uranus and Neptune might have large ice cores, and this is the sort of world that my fictional ice core world Pluton once resembled.

Sounds like such "stripped icy giant" world would basically be a very big Panthalassic world.

How thick is Neptune's atmosphere, and if it was removed, to what extent would the icy core (if any) melt due to internal pressure release?

I'm not sure... you'd get phase changes in the upper layers as Ice VI or VII turns to Ice V, Ice III and Ice I. Any water layer (which probably would exist) would do odd things too - if it's exposed it would freeze, obviously, and make an Ice I layer. I don't know if the centre would be Ice VIII, it depends on the temperature there - it might be high enough...

Either way, it'd be fairly wacky .