© Charles Chandler
In the standard model, the planets in our solar system formed from the same accretion disc as the Sun. (See Figure 1.)
Standard model of stellar and planetary formation, credit Shu et al. (1987), courtesy NASA
This would explain why all of the planets orbit the Sun in the same direction that the Sun rotates on its axis. But it does not explain why all of the planets (except Venus) also rotate around their own axes in the same direction. If a strip of the accretion disc condensed into a planet, the net angular momentum would be retrograde. This is because the inner track orbits faster than the outer, such that its centrifugal force matches the greater gravity nearer the Sun. So all of the planets should rotate in the opposite direction of their orbits.
The standard model also does not explain why the planets are made of fundamentally different stuff compared to the interplanetary medium. While the IPM
is mainly hydrogen, the planets are mainly heavy elements.
It's somewhat more likely that the planets condensed from the same dusty plasma as the Sun, and in the same general vicinity, but the dusty plasma wasn't perfectly symmetrical, and various masses condensed at various points. All of these implosions shared the same angular momentum, even if they didn't have precisely the same target. Thus the orbs would all come to rotate on their axes the same way (except for Venus), and orbit the Sun the same way.
And at least some of the planets might have actually ignited into stars once formed.1
Here we should note that there are many binary and even trinary stellar systems throughout the Universe, which wouldn't make sense if the only object that gets to be a star is whatever is at the center of the accretion disc. The fact that we don't see systems with more than three stars might just be because of the great distances separating us from them. If all of the planets in our solar system were stars too, the whole thing would still appear as a point source to our nearest neighbor outside of our solar system.
If this is correct, the difference between a star and a planet is not a function of position within an accretion disc, but rather, it is a stage in an evolutionary process, wherein planets are simply further along. If so, the heavy elements were fused in situ
during the stellar phase, and were not present in the primordial dusty plasma. In the late stage, the "stars" have lost their outer layers, and are now showing only their heavy-element cores. Thus planetary science is rightfully an extension of stellar theory, not a totally different discipline, and organizing principles identified in the study of the Sun should be used as the pretext. To quote from the relevant section in the discussion of the solar interior
|Figure 2. Charge Separation Under Pressure|
|At left is an abstract representation of a normal crystal lattice, using the familiar icon for an atom, and showing connections of electron shells. At right, extreme pressure has forced the expulsion of one of the electrons from the atom in the center. The expelled electron is to be found just outside, wherever there is room for it, while attracted to the positive ion by the electric force.
It is well-known that at high pressures, matter gets ionized.2
This is because of the Pauli Exclusion Principle, whereby no two identical fermions (i.e., particles with half-integer spins, such as electrons) may simultaneously occupy the same quantum state in the same location. If atoms are pressed too close together, the electron shells of neighboring atoms overlap, and the conflict forces the liberation of one of the electrons. The extra force required to do this accounts for the incompressibility of liquids and solids.3,4,5
(See Figure 2
The same is true even for supercritical fluids — even though they're too hot for crystal lattices, and thus have a plasticity uncharacteristic of their subcritical solid regimes, once compressed down to the density of a solid, they become just as incompressible as subcritical solids.6,7
This fact isn't salient in the larger body of studies that have been done on supercritical fluids at less extreme pressures, and there's actually one place in the phase diagram where supercritical fluids are compressible beyond even the ideal gas laws — just above the critical temperature. (See the Nelson-Obert charts
, and the closely spaced density lines just above the CP in Figure 3
.) Nevertheless, the fluid is as incompressible as ever once it achieves its solid density. (See Figure 4
at its critical temperature of 31 °C, when subjected to 300 GPa (i.e., 3 million
bars), has a density of 1400 kg/m3
, which isn't much above its solid density below the triple point. So supercritical fluids still have a modulus of elasticity beginning at the solid density, but that isn't what we'd call compressibility, certainly not in line with the ideal gas laws.
Thus the Pauli Exclusion Principle holds even for supercritical fluids. Monoatomic matter above the critical point isn't constrained by covalent bonds. But when two atoms are forcibly pushed together, the first conflict will be between the outer electrons. If the pressure is greater than the ionization potential of the atoms, the conflict results in the expulsion of electrons, leaving a strong electrostatic repulsion between the positively charged atomic nuclei, and further compression has to fight the Coulomb force. This marks the transition from compressibility to elasticity, which is very different. The Quantum Mechanics term for this effect is electron degeneracy pressure (EDP
), though the Pauli Exclusion Principle predated QM, and is not reliant on it.
If the pressure is coming from gravitational loading, it increases with depth, meaning greater compression, and atoms packed closer together. At the threshold for EDP
, electrons are expelled, and they have nowhere to go but up, where they will find room between atoms that aren't as tightly packed. Thus the expelled electrons are forced to a higher altitude, leaving positive ions below.
The implication not typically considered is that a charge separation has occurred, creating current-free double-layers (CFDLs
) — they are layers of opposite charges, with a powerful electric field between them, but there is no current responding to the field, because something prevents it. In this case, it's gravity & EDP
preventing charge recombination.
Thus the pretext for the study of a planet is that the interior is separated into oppositely charged layers, bound tightly together by the electric force. Fluctuations in the pressure will then drive electric currents across the boundaries between these layers. (So the double-layers are not entirely current-free.) In the Sun, the energy released is obviously quite robust, while in planets, it is barely more than the ambient energy in the interplanetary medium. Nevertheless, CFDLs
are the organizing principle, and disruptions in the layers are responsible for planetary dynamics, including earthquakes, volcanoes, climate change, etc.
1. Wolynski, J. (2012): The General Theory of Stellar Metamorphosis. ⇧
2. Saumon, D.; Chabrier, G. (1992): Fluid hydrogen at high density: Pressure ionization. Physical Review A, 46 (4): 2084-2100 ⇧
3. Dyson, F. J.; Lenard, A. (1967): Stability of Matter. I. Journal of Mathematical Physics, 8 (3): 423-434 ⇧
4. Lenard, A.; Dyson, F. J. (1968): Stability of Matter. II. Journal of Mathematical Physics, 9 (5): 698-711 ⇧
5. Dyson, F. J. (1967): Ground‐State Energy of a Finite System of Charged Particles. Journal of Mathematical Physics, 8 (8): 1538-1545 ⇧
6. Otles, S. (2016): Supercritical Fluids — Density Considerations. ⇧
7. Tosatti, E. et al. (2009): High-pressure polymeric phases of carbon dioxide. Proceedings of the National Academy of Sciences, 106 (15): 6077-6081 ⇧