SL106: How are Solar Systems formed?
David Noel
<davidn@aoi.com.au>
Ben Franklin Centre for Theoretical Research
PO Box 27, Subiaco, WA 6008, Australia.
About Solar Systems
Solar System is the term used to describe the entourage of planets, moons, and other bodies found surrounding, and under the gravitational influence of, a star.
Until 1992, the only solar system of which we had any detailed knowledge was our own -- the eight planets, hundreds of moons, and asteroids and other bodies orbiting our Sun. Since then, hundreds of exoplanets have been found -- planets orbiting other stars.
So theories about how solar systems came into being were till recently based upon knowledge of our own Solar System. These theories have not been basically changed because of exoplanet data. And almost all of these theories are wrong, in two ways.
First wrong assumption -- sun/planet co-formation
The first wrong assumption made in most theories of solar-system formation is that the central star and the surrounding planets were made as part of the same process.
Why is this assumed? When looked at closely, this assumption has no justification. Sure, the different bodies were probably formed during the same period, one in which accumulation and aggregation of interstellar material (Oort Soup) had built up to a respectable level, but why did they have to be formed together? There are no obvious laws of physics which would allow this.
Instead, a better explanation is that stars, planets, and other bodies were formed in separate acts of aggregation, not as part of a single process. Once formed, the different bodies would move into gravitational equilibrium, with smaller bodies settling into orbits about more massive ones. Importantly, these orbits would be randomly oriented with respect to the plane of rotation of the central body.
The mistake of co-formation is represented in the idea of protoplanetary discs, with smaller bodies lying in a plane around a star, as in Figure F1, where it is assumed that this disc material is in the process of aggregating into planets, moons, and other smaller bodies.
Fig. SL106-F1. Artist's representation of a Protoplanetary Disc. From [A].
It all looks reasonable until the situation is examined more closely. First, there are no physical processes known by which such a disc could be set up during star formation. And why should this disc be oriented in the plane of rotation of the star, as is invariably the case?
The increasing knowledge of exoplanets has also thrown up a killer obstacle to the protoplanetary disc idea. Many systems have been found with giant planets orbiting quite close to their star, in positions where the disc just would not provide enough material for their formation.
Wait on, what about images obtained from telescopes which appear to show actual protoplanetary discs? The explanation for this is given below. We know, in our own Solar System, that the eight planets lie in a single plane to an accuracy of about 7 degrees, Why is this?
Equatorial forcing and normalization of planetary orbits
If our solar-system planets originally had orbits of random inclination to the Sun's equatorial plane, how have they been moved down into this plane? The answer is in a gravitational influence called Equatorial Forcing. Briefly, if smaller-mass bodies have orbits about a massive central body, equatorial forcing acts to bring the direction and plane of the smaller body's rotation closer to the direction and plane of the central body.
There is more detail on this in "P1: The Cosmic Smog model for solar system formation" [A]. Equatorial forcing is an aspect of Spin Gravity, covered in Einstein's Theory of General Relativity, where it has been called "Frame Dragging". More detail on Spin Gravity can be found in "BS806: Mass Gravity and Spin Gravity: Adjusting the Universe" [B].
In [A] it is shown how equatorial forcing has its greatest effects closest to the massive central star, these effects diminishing with distance from the star. So all the planets (and asteroids) orbit more or less within the Sun's equatorial plane, while Kuiper Belt objects (the next furthest out) such as Pluto have orbital inclinations up to 20 degrees or more from this plane.
Comets coming from the inner Oort Cloud have even more inclined orbits, and on moving further out into the Oort Cloud, orbits become random with respect to the Sun. Figure F2 shows how this results in the Sun with its closer companions lying in a plane, without any solid bodies in the space above and below it, and more distant bodies orbiting at higher and higher angles, until the more distant Oort Cloud forms a sphere of objects. Such a distribution could not result from a protoplanetary disc.
Fig. SL106-F2. The Solar System, Kuiper Belt, and Oort Cloud. From [A].
So the conclusion is that all the Sun's companions are captured bodies, all formed separately. This includes all the moons of planets. That they are independent captures is shown by their very varied nature and orbits, some of which are retrograde -- they orbit their planet in the opposite sense to the rest, and to the direction of rotation of their planet.
All these moons orbit close to the equator of their planet, having been brought down to this plane by equatorial forcing. Tellingly, no one has suggested that moons formed from a "proto-lunary" disc. So moons, too, have been individually captured, and show a wide variety of compositions and internal structure. There is no fundamental difference between a small planet and a large moon, or between a small moon and a large asteroid, it's just the chance of capture.
So star systems which appear to have protoplanetary discs are just ones where equatorial forcing has brought most of the closer solid bodies down to the equatorial plane of the star -- we are seeing the star after gravitational forces have been active.
Second wrong assumption -- planets formed at their present distance from their star.
Some of the planets may well have formed at roughly their present distance from their star, but this is not necessarily so.
We think of the Milky Way galaxy as a rotating disc, with each star in its proper place in the disc, but in fact individual components (the stars) may have their own quite large movements relative to the rest. Our Sun is moving through its region of galactic space at around 370 km/sec relative to the other stars. Most of the stars in our close vicinity are travellers -- moving relative to their neighbours.
In "OC407: Chaos In Oort" [C] it is shown how a small star (and its companion) passed through our own Sun's Oort Cloud as recently as 70,000 years ago (Figure F3).
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Fig. SL106-F3. Scholz's Star passing through our Oort Cloud. From [C].
So as well as planets and other bodies formed in the immediate vicinity, stars may capture or harvest other bodies which they move close by to in their travels. Our Solar System has a radius of about 100 AU (Astronomical Units, the Sun-Earth distance). In [C] it is calculated that if the Sun acted as a net, scooping up bodies falling within a 100 AU radius cylinder in its travels, it could sieve through the volume of the entire Oort Cloud in about 217 million years -- less than a twentieth of the Earth's lifetime.
Answers to a few puzzles
The Late Heavy Bombardment (LHB) is a period of intense asteroid and comet impacts that occurred in the inner Solar System, roughly 4 billion years ago. Earlier ideas for the cause of the LHB suggest movement of the giant planets within the Solar System; these ideas mostly lack credible physical-law support or evidence.
The explanation for solar system formation given above leads to a natural explanation of the Late Heavy Bombardment. Spin Gravity is much weaker than Mass Gravity (Newtonian gravity), and so shows up mostly over extended times or distances.
In the current model, from a birth time of about 4.7 billion years, the first 0.7 billion years was a period in which planetary and asteroid orbits were being brought down into the equatorial plane of the Sun. This concentration would naturally lead to increased collisions, and hence increased impact of debris on the planets.
It's of interest that Pluto's elliptical orbit, more than 17 degrees from the solar-system plane, at times takes it within the orbit of Neptune, the furthest planet. At present Neptune and Pluto cannot collide, because their orbits do not overlap and a phenomenon called resonance keeps them apart. But as equatorial forcing brings Pluto's orbit down into the equatorial plane, Pluto and its moons will end up captured as moons of Neptune.
Planetary Rotation Periods. The Earth and Mars each rotate in around 24 hours, and the outer planets rather faster, Jupiter taking just under 10 hours. But Venus and Mercury each take fractions of a year to rotate, with Venus actually retrograde (rotating in the opposite sense to other solar-system objects). Why is this so?
The simple answer is, that as Equatorial Forcing applies to planetary rotations as well as planetary orbits, when Venus and Mercury were captured, each had their own fairly rapid rotation, but in a retrograde manner. Equatorial forcing has sucked out most of this rotation, over many millions of years.
Planetary Tilts. All the planets have rotation axes tilted with respect to the equatorial plane, from 3 degrees for Jupiter up to 30 degrees for Neptune, with Uranus lying almost on its side (82 degrees and retrograde) and Venus also retrograde. This mishmash can naturally be expected from the capture of individually formed bodies with random axial tilts.
Mercury. Mercury is a rather poor fit into the general pattern, with a notably high inclination (7 degrees), a notably elliptical orbit, and an unexplained relatively high density.
All these points are explicable if Mercury is a relatively recent capture which originated at a later time than most of the solar system material. Equatorial forcing has had less time to work.
Ockham wins again
The picture of solar system formation presented here is logical and realistic, and is also simple. It stands without relying on unexplained encounters and giant collisions between bodies.
Applying Ockham's Razor logically leads to its acceptance -- at least until such time as an even simpler explanation is found.
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AOI articles with relevant evidence
[A]. P1: The Cosmic Smog model for solar system formation, and the nature of 'Dark Matter' .
[B]. BS806: Mass Gravity and Spin Gravity: Adjusting the Universe
[C]. OC407: Chaos In Oort .
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SL106 Commenced writing 2025 Apr 19. First version 1.0 on Web 2025 Apr 23.
