Trace methane in Uranus and Neptune, condensing into diamonds

[Dukon]

TL;DR Summary

As diamonds descend to interior and melt is this exo or endothermic?

Uranus and Neptune have roughly an 80-19-1 $H_2$-$He_4$-$CH_4$ mixture. (Of course actual percentages vary but those are rough values for sake of this simplification argument -- unless their actual values are critical to the answer.) Uranus temperature is reported as 2K while Neptune is 20K.

Two questions:

1) Uranus: since STP conditions do not apply inside Uranus, and pressure increases as altitude decreases to core, does anyone know the phase (solid-liquid-gas) for each of the three $H_2$-$He_4$-$CH_4$ inside on the way into the core from the surface? Is Uranus an example of a very large amount of superfluid Helium and so all those strange properties might become even more strange due to the extreme magnitudes of the actual masses in the planet? How would a superfluid behave in these circumstances? Is anyone aware of this topic being analyzed and published in the literature?

1a) the Earth has a solid core in a liquid mantle of very different material content each. As known from meaurements by gravimeters on the Earth surface, it is known that the solid core executes oscillations of roughly a 4 hr period slightly different in the three directions, where the x,y,z axis periods came out as roughly 3.9 for x, 4.1 for y and 4.05 for z (of course published numbers are different than these but these show roughly what is meant by the variations around 4 hrs for all of them.) Duplicating this phenomena behaviour inside Uranus, wouldn't the 81% of material solid hydrogen & methane act as a solid core in this liquid helium "mantle" and wouldn't it too under go such oscillations at periods not around 4hrs but some other value determined the specs of Uranus not of Earth? Is anyone aware of this topic being analyzed and published in the literature?

In other words, is Uranus a giant laboratory for the study of the behaviour of extremely large scale amounts of superfluid Helium?

2) Neptune: 20K not 2K

A source reports a theory for this difference attributing it to the following (use of hard brackets [] are my own thoughts not from the source) increasing pressures below the outer surface layer of Neptune causes the carbon in methane to a) separate out of methane [in what must be an endothermic process to crack the methane], and b) force the extracted Carbon to form diamonds [in again an endothermic process again removing energy from the pressure bath], and so these solid diamonds now fall into the interior, whereupon at the higher pressure core [which is a source of energy for any process] they "melt" thus giving off energy which accounts for the hotter Neptune compared to similar composition Uranus?

However, any energy they might give off at the core, was granted to them on their way from the surface down into the core. So wouldn't this energy exactly balance? What could cause a difference between the energy imparted to the carbon on its way down, versus the energy liberated on their way up?

 

[mjc123]

Melting is an endothermic process.

 

[stefan r]

In other words, is Uranus a giant laboratory for the study of the behaviour of extremely large scale amounts of superfluid Helium?

Superfluid is pretty unlikely. Did you mean supercritical fluid?

Summary:: As diamonds descend to interior and melt is this exo or endothermic?
...[in what must be an endothermic process to crack the methane], and b) force the extracted Carbon to form diamonds [in again an endothermic process again removing energy from the pressure bath], and so these solid diamonds now fall into the interior, whereupon at the higher pressure core [which is a source of energy for any process] they "melt" thus giving off energy which accounts for the hotter Neptune compared to similar composition Uranus?
...

If there is enough pressure formation of diamond will be exo-thermic. The carbon-carbon bonds are tighter than the carbon-hydrogen bonds.

When hydrogen moves through solids like platinum it moves as a proton. I am not sure how relevant that is to the phase transitions in Neptune and Uranus. The protons escaping from a growing crystal would not be surprising. In the water ice phase XVIII the hydrogen ions are fully conducting and migrate easily.

The primary source of heat is gravitational collapse. If you drop an object onto Earth it burns up in the atmosphere. Neptune's core has just as much gravity. If dense materials (like carbon) precipitate and descend from what we call the "surface" toward the core the planet is in a lower energy state. The energy will be released as friction while the crystal or droplet is falling.

In order to gauge the significance of the temperature difference between Neptune and Uranus we would need to know how well the atmospheres are insulating their core.