The solar system has different types of planets and a variety of moons.
Can the nebular hypothesis explain this arrangement of planets & moons and orbits?
This post is probably too long but all the rough details are important for this topic (and hopefully interesting).
On 3/27/2019 I posted about dwarf planets in our solar system.
How did the solar system get like this?
I have gathered many pieces into what should be an easier single narrative to follow.
from wikipedia, about the nebular hypothesis:
The protoplanetary disk is an accretion disk that feeds the central star. Initially very hot, the disk later cools ; here, formation of small dust grains made of rocks and ice is possible. The grains eventually may coagulate into kilometer-sized planetesimals. If the disk is massive enough, the runaway accretions begin, resulting in the rapid—100K to 300K years—formation of Moon- to Mars-sized planetary embryos. Near the star, the planetary embryos go through a stage of violent mergers, producing a few terrestrial planets. The last stage takes approximately 100 million to a billion years
This initial process is not logical.
No matter how high I pile up 'small dust grains' here on Earth so even with help from Earth's gravity, I certainly cannot expect that huge mass will coagulate into anything; definitely not a planetesimal of any size.
A force of compression is required to change the old molecular bonds (in the initial distinct grains, formed after the disk cooled) into a new lattice structure for a cohesive solid. The weak force of Gravity alone is not capable of changing lattice structures in the initial solid particles to the final single solid body. Gravity just holds down the pile on Earth; in space, the separate particles would be moving as a gas. If their temperature were low so they have minimal kinetic energy then gravity could slowly pull them together with no friction but with no shape.
If the individual particles have more mass then their gravity increases but is still weak.
'runaway accretions' is silly. Everything we observe follows expected behaviors in physics. To propose a process will run away clearly states a non-conforming process is being proposed. The hope is one impossibility will succeed and then more can follow with no defined process.
Melting a solid (like the dust grains) breaks its lattice structure (as a solid); that is not proposed here.
The formation of giant planets is a more complicated process. It is thought to occur beyond the frost line, where planetary embryos mainly are made of various types of ice. As a result, they are several times more massive than in the inner part of the protoplanetary disk.
The last stage of rocky planet formation is the merger stage. It begins when only a small number of planetesimals remains and embryos become massive enough to perturb each other, which causes their orbits to become chaotic. During this stage embryos expel remaining planetesimals, and collide with each other. The result of this process, which lasts for 10 to 100 million years, is the formation of a limited number of Earth-sized bodies. Simulations show that the number of surviving planets is on average from 2 to 5. In the Solar System they may be represented by Earth and Venus. Formation of both planets required merging of approximately 10–20 embryos, while an equal number of them were thrown out of the Solar System. Some of the embryos, which originated in the asteroid belt, are thought to have brought water to Earth. Mars and Mercury may be regarded as remaining embryos that survived that rivalry. Rocky planets, which have managed to coalesce, settle eventually into more or less stable orbits, explaining why planetary systems are generally packed to the limit; or, in other words, why they always appear to be at the brink of instability.
The planetesimals are expected to attain orbits so they now (somehow) possess kinetic energy. On a collision that kinetic energy is either maintained in a rebound or it is passed to the many fragments from the impact or to thermal energy when the molecular bonds maintain the solids through the collision. The use of 'simulations implies this process is too complex to define, so this remains an unsolved problem
To propose the gas giants form completely isolated from the terestrials and all planets will simply manage to attain stable orbits given enough time is inadequate for a robust theory.
There are observations that probably should not be ignored by the theory.
The respective planets and moons have individual details not addressed, but should be eventually.
Earth and Moon:
In 2001, a team at the Carnegie Institute of Washington reported the most precise measurement of the isotopic signatures of lunar rocks. To their surprise, the rocks from the Apollo program had the same isotopic signature as rocks from Earth, however they differed from almost all other bodies in the Solar System. Indeed, this observation was unexpected, because most of the material that formed the Moon was thought to come from Theia and it was announced in 2007 that there was less than a 1% chance that Theia and Earth had identical isotopic signatures. Other Apollo lunar samples had in 2012 the same titanium isotopes composition as Earth, which conflicts with what is expected if the Moon formed far from Earth or is derived from Theia. These discrepancies may be explained by variations of the giant impact hypothesis.
The origin of earth and moon is undefined.
Of over 61,000 meteorites that have been found on Earth, 224 were identified as Martian as of January 2019. These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmosphere gases analyzed by spacecraft on Mars.
Why did so many make the long trek?
Jupiter, the largest planet, has Ganymede.
Ganymede is the largest moon and is larger than Mercury and is similar to Mars.
It is the largest moon without a substantial atmosphere, possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field.
Why is Ganymede not in the Sun's orbit with the other terrestrials?
Jupiter also has Callisto, Io, Europa; these 3 are larger than Pluto.
[There] are the flashes of lightning detected in the atmosphere of Jupiter. These electrical discharges can be up to a thousand times as powerful as lightning on Earth.'
Jupiter's magnetic field is fourteen times as strong as that of Earth
Jupiter's other moons:
Thus there may have been several generations of Galilean-mass satellites in Jupiter's early history. Each generation of moons might have spiraled into Jupiter, because of drag from the disk, with new moons then forming from the new debris captured from the solar nebula. By the time the present (possibly fifth) generation formed, the disk had thinned so that it no longer greatly interfered with the moons' orbits.
Callisto is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System not to be properly differentiated.
Callisto is composed of approximately equal amounts of rock and ices, with the lowest density and surface gravity of Jupiter's major moons. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km.
The surface of Callisto is the oldest and most heavily cratered in the Solar System.
Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather intense ionosphere. Callisto is thought to have formed by slow accretion from the disk of the gas and dust that surrounded Jupiter after its formation. Callisto's gradual accretion and the lack of tidal heating meant that not enough heat was available for rapid differentiation. The slow convection in the interior of Callisto, which commenced soon after formation, led to partial differentiation and possibly to the formation of a subsurface ocean at a depth of 100–150 km and a small, rocky core.
Io is the fourth-largest moon, has the highest density of all the moons, and has the least amount of water of any known astronomical object in the Solar System.
With over 400 active volcanoes, Io is the most geologically active object in the Solar System.
Io's volcanism is responsible for many of its unique features. Numerous extensive lava flows, several more than 500 km (300 mi) in length, also mark the surface. The materials produced by this volcanism make up Io's thin, patchy atmosphere and Jupiter's extensive magnetosphere. Io's volcanic ejecta also produce a large plasma torus around Jupiter.
Europa is the sixth-largest moon in the Solar System.
Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. It has a very thin atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, but craters are relatively few. In addition to Earth-bound telescope observations, Europa has been examined by a succession of space probe flybys, the first occurring in the early 1970s.
Europa has the smoothest surface of any known solid object in the Solar System. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably harbour extraterrestrial life. The predominant model suggests that heat from tidal flexing causes the ocean to remain liquid and drives ice movement similar to plate tectonics, absorbing chemicals from the surface into the ocean below. Sea salt from a subsurface ocean may be coating some geological features on Europa, suggesting that the ocean is interacting with the sea floor. In addition, the Hubble Space Telescope detected water vapor plumes similar to those observed on Saturn's moon Enceladus, which are thought to be caused by erupting cryogeysers
Saturn, the 2nd largest planet, has Titan, the second largest moon.
Saturn's interior is probably composed of a core of iron–nickel and rock (silicon and oxygen compounds). This core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally a gaseous outer layer. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's.
The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, and only 13 of which have diameters larger than 50 kilometers, as well as dense rings with complex orbital motions of their own. Seven Saturnian moons are large enough to be ellipsoidal in shape, yet only two of those, Titan and Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System (after Jupiter's Ganymede), with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes found nowhere else in the solar system; and Enceladus since its chemical composition is similar to that of comets. In particular, Enceladus emits jets of gas and dust, which could indicate the presence of liquid water under its south pole region, and may have a global ocean below its surface.
Saturn's moon Iapetus
Iapetus or Japetus is the eleventh-largest in the Solar System, and the largest body in the Solar System known not to be in hydrostatic equilibrium. Iapetus is best known for its dramatic "two-tone" coloration. Discoveries by the Cassini mission in 2007 revealed several other unusual features, such as a massive equatorial ridge running three-quarters of the way around the moon.
Unlike most of the large moons, its overall shape is neither spherical nor ellipsoid, but has a bulging waistline and squashed poles; also, its unique equatorial ridge is so high that it visibly distorts Iapetus's shape even when viewed from a distance. These features often lead it to be characterized as walnut-shaped.
Iapetus is heavily cratered, and Cassini images have revealed large impact basins, at least five of which are over 350 km (220 mi) wide. The largest, Turgis, has a diameter of 580 km (360 mi); its rim is extremely steep and includes a scarp about 15 km (9.3 mi) high.
More-recent studies, however, suggest that all of Saturn's moons inward of Titan are no more than 100 million years old; thus, Iapetus is unlikely to have formed in the same series of collisions as Rhea and all the other moons inward of Titan, and—along with Titan—may be a primordial satellite.
Like Dione and Rhea, the surface of Thetys is mostly icy.
Enceladus is the most reflective body in the solar system.
The relatively large Hyperion is locked in a resonance with Titan.
Saturn's moon Enceledus
Enceladus is the sixth-largest moon of Saturn; Enceladus is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Despite its small size, Enceladus has a wide range of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrains.
from a NASA reference:
This hiss-like noise created by the electrons is one sign of the magnetic connection between Saturn and Enceladus, which also creates a glowing ultraviolet "footprint" near Saturn's north pole. Electron beams detected by the Cassini plasma spectrometer and magnetic field disturbances detected by Cassini's magnetometer also provided signs of the electrical circuit between Saturn and Enceladus.
The isotope ratio in the water on earth is like that on Saturn, its rings, and its moon Encedelas (unlike elsewhere); How did that come about when the objects are on opposing sides of the defined frost line?
Titan is the 2nd largest moon and is also larger than Mercury and has an atmosphere with Nitrogen dominant like Earth; these are the only two thick atmospheres with N dominant.
Why is Titan not in the Sun's orbit with the other terrestrials?
The rings of Saturn may be iconic, but there was a time when the majestic gas giant existed without its distinctive halo. In fact, the rings may have formed much later than the planet itself, according to a new analysis of gravity science data from NASA's Cassini spacecraft.
The findings indicate that Saturn's rings formed between 10 million and 100 million years ago. From our planet's perspective, that means Saturn's rings may have formed during the age of dinosaurs.
The nebular hypothesis should describe how the rings were formed. This phenomenon is important because Jupiter, Uranus, and Neptune also have rings though fainter than Saturn's.
Uranus is the 3rd largest planet by diameter.
Uranus has an extreme axial tilt for its rotation.
Astronomers think that a large protoplanet smashed into Uranus billions of years ago. This collision set the planet tumbling. Eventually it settles into its current axial tilt.
In this scenario why did a proto planet deviate so far out its orbit to smash into Uranus? The adjacent planets, Saturn and Neptune, are huge so its orbit must be distant so where did it come from and where is it now, after such a violent collision? What is the complete explanation? I wonder if anyone tried a model of Uranus and moved in another body to determine what it would take (mass, diameter, trajectory) to get the observed tilt? Would it require another gas giant or larger? That answer should be part of developing the hypothesis because it is so important for its impact on the transitions in the configuration.
If the angle of approach must be outside of the solar system plane then that is another complication. I would expect the results of such an analysis for the Uranus tilt to be quite newsworthy, since it remains a mystery (as the theory has no details).
Neptune the 3rd largest planet by mass, has Triton.
Triton is the 7th largest moon and is also larger than Pluto and has a thin atmosphere with Nitrogen dominant like Earth or Titan. Why is Triton not in the Sun's orbit with the other terrestrials, or why did Neptune get it rather than Jupiter or Saturn?
An orbital resonance implies the two bodies must have been adjacent (or nearly) before their respective orbits took them away and still return them close after a number of orbits, to re-establish the resonance.
Eris is almost the same size as Pluto, but is far beyond Neptune.
Ceres in the asteroid belt has a similar size to several moons and several TNO. The asteroid belt and the TNO regions need an explanation; Ceres is spherical not a fragment.
This has been proposed for the small bodies, inner planets and for many craters:
The Late Heavy Bombardment (abbreviated LHB) is an event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago. During this interval, a disproportionately large number of asteroids are theorized to have collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth, and Mars.
The Late Heavy Bombardment happened after the Earth and other rocky planets had formed and accreted most of their mass, but still quite early in Earth's history.
Evidence for the LHB derives from lunar samples brought back by the Apollo astronauts. Isotopic dating of Moon rocks implies that most impact melts occurred in a rather narrow interval of time. Several hypotheses attempt to explain the apparent spike in the flux of impactors (i.e. asteroids and comets) in the inner Solar System, but no consensus yet exists. The Nice model, popular among planetary scientists, postulates that the giant planets underwent orbital migration and in doing so, scattered objects in the asteroid and/or Kuiper belts into eccentric orbits, and into the path of the terrestrial planets. Other researchers argue that the lunar sample data do not require a cataclysmic cratering event near 3.9 Ga, and that the apparent clustering of impact-melt ages near this time is an artifact of sampling materials retrieved from a single large impact basin. They also note that the rate of impact cratering could differ significantly between the outer and inner zones of the Solar System.
This is still a mystery given 'no consensus yet.'
On 3/11 I posted about an alternate theory about why nearly all craters in the solar system are round; the consensus explanation is illogical, where the same crater shape results regardless of its trajectory.
The most precise orbital resonance is between Venus and Earth. These planets meet 5 times during 8 Earth years and during 13 Venus years. Then their resonance ratio is 13:8 ... After those 8 ea-years, the planets meet on almost a same place.
This difference makes the higher-order wave of the resonance. Only in the case of Earth/Venus, this higher-order wave among direct neighbours is in retrograde (counter-orbital) direction. All outer planets have got the higher-order wave in prograde direction among neighbours.
It takes 243 years (30x the 8-year cycle + 2 meetings) between the planets meet on an almost-same place.
The resonance shape gets little modified occasionally, mostly by perturbations by Jupiter, but is always restores briefly. Hence, the resonance keeps the orbits stable despite of all perturbations.
Jupiter and Saturn resonate in 5:2 rate, they meet 3 times during 5 Jupiter years and 2 Saturn years, with a difference of 242 ea-days in orbital (prograde) direction .
Saturn and Uranus resonate in 20:7 rate .
Pluto is locked into a 3:2 resonance with Neptune. For every 3 orbits of the Sun completed by Neptune, Pluto completes 2 orbits.
One might expect resonances are a clue to possible sequences.
Are any of these resonances a result of specific events not fully defined in the hypothesis?
The excerpt for LHB mentions the gas giants probably moved about but this is a possibility without details.
Clearly when reading details about Uranus and the moons of the Gas Giants cosmologists recognize there had to be major disturbances in the solar system. Jupiter is assumed to capture and release moons multiple times. There are also references to electromagnetic effects so it is clearly recognized gravity does not drive many behaviors. Jupiter and Saturn have strong electric and magnetic fields, as does the Sun. These pieces (many mentioned above) have not been integrated into a coherent theory; I find nothing online identified as 'in progress' to convey any progression. One would think that a milestone is newsworthy. I suspect there is still too much uncertainty.
At this point the nebular hypothesis is inadequate as an explanation for our solar system. Cosmologists need to improve this theory.
Cosmologists need more data from the planets, perhaps from soil or atmospheres, to get a better understanding of the history of the solar system.
Unfortunately the process of sending probes to distant planets, real or dwarf, is expensive and takes a very long time. There are limitations with probes in Earth orbit but scientists are innovative with technology.
There is an obvious problem here. The missions need a clear definition of what data are needed but a wrong basis might omit that data which will result in efficient progress of understanding. If we look for only what we expect the important aspects to learn will remain lacking in detail to develop. It appears there are some unlikely proposals; I noted a few; they are a burden. Perhaps there is reluctance toward innovation.
There are too many unknowns preventing a comprehensive theory for explaining our solar system.
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