How the planets formed?

[Cheap Astronomy]

Hi,

There seems to be 2 theories going around:

1) the solar nebular/Kant model where a big gas cloud collapsed down into a disk with the Sun at the centre and the planets forming from accretion of the remaining materials in the disk; or

2) the gas cloud just collapsed down into the Sun - which, when it reached a critical density and fusion took off in its core, underwent a violent hiccupy sort of explosion throwing out lots of matter which was what accreted down to form the planets.

I had thought scientific consensus was pretty much aligned with theory 1), but have recently seen 2) espoused in some seemingly authoritative places.

Welcome comments. If 2) is prevailing theory, what was the nature of the outflung material? Had it undergone any fusion itself in the "hiccupy sort of explosion"?

Thanks

[astromark]

I would not want to cheapen your argument but I think a combination of both is the answer you seek.
By the forcess of gravitational attraction did the collesing begin and when a stellar mass was formed some material was ejected. A confusing mixture of 1 and 2 perhaps., but is the answer to be found by a compromise.

[Paul Beardsley]

I cannot answer your question now, but I am planning on doing a course on planetary formation with the Open University some time next year. I will try and remember to get back to you if you are still looking for answers.

[Cheap Astronomy]

Thanks Paul, I will keep logging in on an approximately weekly basis awaiting your answer.

[Hornblower]

Hi,

There seems to be 2 theories going around:

1) the solar nebular/Kant model where a big gas cloud collapsed down into a disk with the Sun at the centre and the planets forming from accretion of the remaining materials in the disk; or

2) the gas cloud just collapsed down into the Sun - which, when it reached a critical density and fusion took off in its core, underwent a violent hiccupy sort of explosion throwing out lots of matter which was what accreted down to form the planets.

I had thought scientific consensus was pretty much aligned with theory 1), but have recently seen 2) espoused in some seemingly authoritative places.

Welcome comments. If 2) is prevailing theory, what was the nature of the outflung material? Had it undergone any fusion itself in the "hiccupy sort of explosion"?

Thanks

Can you identify the "seemingly authorative places" and the people who inhabit them?

The Kant model, augmented with electromagnetic forces which Kant could not have anticipated, does a pretty good job of accounting for the distribution of mass and angular momentum.

[Ken G]

Not only have I not heard (2), it is pretty easy to refute it. An important point about the planets is that most of the angular momentum of the solar system is "stored" in their orbital motions. Had they ever been in the Sun, to get them to "hiccup" out, you'd need to get the majority of the angular momentum in the Sun to participate in the hiccup. That doesn't even count the angular momentum in the associated hydrogen gas that would have to come along. It seems to me that any proponent of (2) would have to pretty much not understand conservation of angular momentum, which more or less rules out all reasonably informed astronomers.

[rodin]

I'm with Kant too from what I read here. Also I am interested in a mechanism that accounts for the nature of planets. As a matter of interest, does Kant predict the chemistry and physics of planets as well as size and distribution?

Sorry being lazy - really should read about this more first...

[astromark]

I think we all understand the stellar disk formation from material available to it some 4.5 billion years ago. The relentless force of gravity and rotational velocities doing the obvious. At that moment when the mass and density dictated a ignition of the stellar core meaning the star was born. Was there ever a violent outburst ? I do not think we have proof of that. The general cleaning up of the system took many if not billions of years. The chaos of the early solar system is not the same as your point 2. The mechanism involved is understood. From where does this other theories come ?

[Veeger]

I think one of the puzzling aspects of planet formation is how certain planets ended up with iron cores (or so we believe). Apparently the hydrogen cloud was fairly rich in iron and amazingly a lot of the iron ended up in planets quite far from the sun's core.

[kleindoofy]

... does Kant predict the chemistry and physics of planets as well as size and distribution? ...

Considering all the factors involved, that would be more or less impossible.

Let's look at a smaller but known system to demonstrate, although the comparison it not 1 to 1: the 6 out of 49 lotter system.

In this system, 49 numbered balls drop out of a tray into a rotating drum. One by one, six balls are scooped up, i.e. the winning lottery numbers. Now, given enough data about the tray, the balls, the drum, the scoop, the temperature, etc., mathematics should be able to predict exactly which numbers will be drawn in any given drawing, and in which order.

In reality however, this is presently not possible. The factors involved are so complex and minute, that it is outside of our power to list and measure them in any usable way.

Now, if week by week, the equipment stayed *exactly* the same, even in the smallest of small details and the balls were placed in the tray in *exactly* the same way (they are always in the same position), and all other factors of the drawing remained *perfectly* and *exactly* the same, right down to the atomic level, then the same numbers would come up every week.

This is obviously not the case. Long term observation has shown that the winning numbers are, in fact, totally random. This can only mean that the tiny, tiny, itsi-bitsy differences which enter the system week to week are enough to alter the outcome making it unpredictable. E.g., placement of the balls in the tray, exact position of the tray, dust, moisture etc. on the balls and in the drum, the speed of the drum, the humidity and temperature, etc., etc., etc.

The lottery machinery is a closed and known system. The outcome is nevertheless unpredictable.

A planetary nebula and the forces involved are infinitely more complex. Even the smallest of factors will influence the outcome.

Although certain generalisations will be applicable, even the exact same nebula with one or two altered parameters will produce a different result.

[korjik]

I think one of the puzzling aspects of planet formation is how certain planets ended up with iron cores (or so we believe). Apparently the hydrogen cloud was fairly rich in iron and amazingly a lot of the iron ended up in planets quite far from the sun's core.

If you assume that the nebula that created the Sun had the same mix of elements throughout, then the composition of the planets isnt remarkable.

Jupiter and Saturn have a composition very similar to the Sun. If you take into account the increasing temperature of the proto-Sun, and that it would blow away alot of the lighter elements from the inner solar system, then the composition of the inner planets is explained.

There isnt an excess of iron, there is a lack of hydrogen and helium.

[astromark]

'Kliendoofy' I liked your analogy...could I have a list of those numbers before Saturday
please...
'korjik' taking what you have explained as true might suggest a solar wind did the clean up more so than a explosion. The chaotic early system would have been 'Dangerous' and temporary. The first half billion or so must have been turbulent. Yet still we are here. As has now been well covered it would be impossible to reconstruct the model of all those variables into a simple explanation. There is not one.

[Jeff Root]

I have never heard (2) either. At the end of its formation, the protosun
became a T-Tauri star, very bright and spewing out a solar wind so strong
that it was able to blow away the outer hydrogen and helium atmospheres
of the terrestrial planets. That occurred at about the same time as fusion
was getting started in the Sun's core, I think, but it was not a result of
the fusion. Becoming a T-Tauri star would be what ended the Sun's
accumulation of matter. If it hadn't become a T-Tauri star, it would not
have blown away the dust and gas in the protosolar disk, and it would
have kept on growing in mass.

It is believed that the protosun lost most of its angular momentum to
the protosolar disk via intense magnetic fields originating within the Sun.
The fields accelerated the dust and gas before and while the planets
were forming.

-- Jeff, in Minneapolis

[Ken G]

I think I see what is happening-- the model the OP is probably talking about is the "X-wind" model of Frank Shu and others, which is a well regarded model. However, the material that forms the planets does not come from inside the Sun, rather it is in the disk around the Sun where the angular momentum is. However, it is much closer to the Sun than where the planets form. So some material falls into the Sun, and other material is "flung out", and this model can explain why you get substances appearing at distances that seem way too far out to be hot enough to have the "chondrule" structure they have. It's pretty detailed, but it does have some of the attributes of the OP, but it is still all happening to the disk, not to the Sun.

[Veeger]

Good point, korjik, I had neglected to think about the effect of the solar wind.

If you assume that the nebula that created the Sun had the same mix of elements throughout, then the composition of the planets isnt remarkable.

What exactly do you mean by "the same mix of elements throughout"? Equal proportions of elements or the same proportions as found in the solar system today? Given, that it may have taken millions, perhaps a billion years for the sun to ..er.. fire up, doesn't it seem likely that the heavier elements would have migrated toward the center of mass? That is, shouldn't they be in the sun's core - not the inner planets?

[Jeff Root]

Veeger,

By "the same mix of elements throughout", korjik meant a uniform
composition throughought the pre-solar nebula. As far as I know, there
is no mechanism that would cause heavier elements to preferentially fall
into the Sun. Everything was in orbits. Lighter elements, however, would
have preferentially been blown away from the Sun by solar wind.

-- Jeff, in Minneapolis

[Cheap Astronomy]

Can you identify the "seemingly authorative places" and the people who inhabit them?

The Kant model, augmented with electromagnetic forces which Kant could not have anticipated, does a pretty good job of accounting for the distribution of mass and angular momentum.

For example, a plaque at Deep Space Network visitors centre (implying a NASA/JPL source).

[snowflakeuniverse]

Hi Cheap Astronomy

You asked for some advice about two planetary formation models, ie, the nebular cloud model or the “hiccup model”,

The “hiccup” model is the correct model, contrary to what has been posted so far.

If you have a copy of the undergraduate/graduate course book called “Modern Astrophysics", written by Bradley W Carroll and Dale A Ostlie on page 890 you can find the information about issues relating to the angular momentum distribution which is one of the primary reasons for the “hiccup “ model.

To avoid copyright issues I will briefly summarize the problem described in this excellent text.

If the planets formed as a result of the collapse of a nebular cloud, it would do so with no part of the cloud moving much faster than any other near by part since kinematic collisions would disperse and even out the velocities, ie one part of the cloud would not be spinning 10 times faster than some nearby part of the cloud.

As the cloud collapsed due to gravitational interaction, the sun and planets would form, preserving the angular momentum existing within the nebular cloud.

One would expect that the sun would contain most of the angular momentum, and would be rapidly rotating, just as a spinning skater increases the rate of rotation when the arms are pulled inwards, the sun should increase the rate of rotation as in-falling matter builds up the suns mass.

What is found is that even though the sun contains 99.9 percent of the mass of the solar system it contains less than 1 percent of the angular momentum. The angular momentum is dispersed out towards Jupiter.

Also, compounding the issue is the fact that the axis of rotation of the sun is inclined 7 degrees from the average momentum vector of all the planets.

Something radically disturbed the formation of the solar system.

As an “Against the Mainstream” expert, this observation provided evidence compatible with my model in which the effect of gravity was greater due to the increased density of all systems. My model would predict that stars would be much smaller and evolve much more quickly, even to the point where they would become a mini star supernova. I contend that this mini supernova in our solar system disbursed the angular momentum of the solar system outwards, smashed the planet that was forming near the asteroid belt, responsible for the object that would hit our Earth forming the Earth moon system, flashed some moons to be two toned, tipped the axis of rotation 98 degres of Uranus and produced the Ort cloud, and most of the Asteroids and meteors found in the solar system today.

A rather big “hic up”. But this is an “against the mainstream” explanation for what is observed.

Snowflake

[snowflakeuniverse]

Hi Jeff Root

You stated,
It is believed that the protosun lost most of its angular momentum to
the protosolar disk via intense magnetic fields originating within the Sun.
The fields accelerated the dust and gas before and while the planets
were forming.

This explanation became obsolete or certainly challenged with the discovery of large Jupiter sized planets near their mother stars. How could these large planets form when the radiant pressure and magnetic fields from the their mother star should have blown all their mass outwards? (Which was the explanation given to explain why the inner planets of our solar system contains so little Hydrogen and Helium). (It is my contention that a mini supernova occurred in the past, blowing off all the atmospheres of the inner planets, leaving the heavy cores behind, which then became the new seeds for atmosphere building.)

Snowflake

[Ken G]

The “hiccup” model is the correct model, contrary to what has been posted so far....Something radically disturbed the formation of the solar system.

The latter fact alone does not support the former claim, because it has always been obvious that the nebular model also requires significant modification by transport of angular momentum. Not just to the planets, but out of the solar system altogether. Magnetic fields are generally invoked for that. What's more, the way the "hiccup" model was expressed above is that the material left the Sun itself after it formed, rather than a transport mechanism operating on the disk around the Sun. Even Shu's "X-wind" model does not have that feature, so I'm not aware of a single mainstream model that does. That's why I said I suspect the OP did not mean to talk about moving material out of the Sun after it formed, but rather first forming a disk around the Sun where most of the angular momentum is, and then having complicated angular momentum transport mechanisms move that material around.

Indeed, I wonder if it would even be possible to form the Sun in the first place if the angular momentum we find in the planets was ever in the Sun, though I haven't checked that.

A rather big “hic up”. But this is an “against the mainstream” explanation for what is observed.

...and belongs in the ATM section.

[Ken G]

This explanation became obsolete or certainly challenged with the discovery of large Jupiter sized planets near their mother stars. How could these large planets form when the radiant pressure and magnetic fields from the their mother star should have blown all their mass outwards?

That explanation is far from obsolete, but it certainly needs a lot of fleshing out. The idea about nearby Jupiters is that they may have "migrated" inwards, an idea that also needs a lot of fleshing out. Such is science. We know a lot about stars like the Sun in their early days, and I do not know of a shred of evidence for "mini supernovas", but you should take that to ATM.

[PetersCreek]

But this is an “against the mainstream” explanation for what is observed.

And it is well established that the Q&A forum is not the place to offer ATM explanations. Of course, it's reasonable to discuss competing theories when things aren't completely settled but if you have a model of your own to propose, please do so in the ATM forum.

[Weakly Interacting MP]

Iron sun again snowflakeuniverse? Seems to me this was pretty much shot down already in this forum. I have no intention of hijacking this thread further, but I'ld like to see you re-present your idea in a thread of its own.

C'mon, I dare ya!

[snowflakeuniverse]

Hi Cheap Astronomer

You also asked,

If 2) is prevailing theory, what was the nature of the out flung material? Had it undergone any fusion itself in the "hiccupy sort of explosion"?

There is some evidence of a nuclear explosion 4 to 5 billion years ago. A radioactive form of xenon (called strange xenon) was collected in samples taken from the moon during the Apollo missions. (Other missions in the solar system also found evidence of strange xenon) The only way to produce this element (according to several nuclear physicists) is from a star that has exploded.

Whether or not this material is from our own sun erupting, or some other distant source of ejected material that was ejected into our solar system is debatable.

Snowflake.