What smacked Uranus on its side? Something icy and as massive as Earth, scientists say.

rod

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FYI, Uranus big smack has been in the news over the years. In 2011, this report came out, https://www.sciencedaily.com/releases/2011/10/111006084235.htm, "...However, the simulation threw up an unexpected result: in the above scenario, the moons displayed retrograde motion -- that is to say, they orbited in the opposite direction to that which we observe. Morbidelli's group tweaked their parameters in order to explain this. The surprising discovery was that if Uranus was not tilted in one go, as is commonly thought, but rather was bumped in at least two smaller collisions, then there is a much higher probability of seeing the moons orbit in the direction we observe. This research is at odds with current theories of how planets form, which may now need adjusting. Morbidelli elaborates: "The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk. They should have suffered no giant collisions. The fact that Uranus was hit at least twice suggests that significant impacts were typical in the formation of giant planets. So, the standard theory has to be revised."

I note *tweaked their parameters in order to explain this*. Keep on tweaking the giant impacts. The current report has interesting items in it too for the model, here is another example. https://phys.org/news/2020-04-uranus-oddities-japanese-astronomers.html, "The origins of Uranus' unusual set of properties has now been explained by a research team led by Professor Shigeru Ida from the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology. Their study suggests that early in the history of our solar system, Uranus was struck by a small, icy planet roughly one to three times the mass of the Earth, which tipped the young planet over and left behind its idiosyncratic moon and ring system as a smoking gun."

My observation, like Theia, this 3 earth mass object is an NOO, non-observable object and the impact event, I call a UE or unobserved event. Perhaps a UOE, an unobservable event. Here is something from the abstract, https://www.nature.com/articles/s41550-020-1049-8, "The ice-giant planet Uranus probably underwent a giant impact, given that its spin axis is tilted by 98 degrees1,2,3. That its satellite system is equally inclined and prograde suggests that it was formed as a consequence of the impact. However, the disks predicted by the impact simulations1,3,4 generally have sizes one order smaller and masses two orders larger than those of the observed system at present. Here we show, by means of a theoretical model, that the Uranian satellite formation is regulated by the evolution of the impact-generated disk. Because the vaporization temperature of water ice is low and both Uranus and the impactor are assumed to be ice-dominated, we can conclude that the impact-generated disk has mostly vaporized. We predict that the disk lost a substantial amount of water vapour mass and spread to the levels of the current system until the disk cooled down enough for ice condensation and accretion of icy particles to begin."

More NOOs and UE or UOEs used in the model. Keep *tweaking* :)
 
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Catastrophe

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"I’m wondering if Earth could have smacked Uranus taking a large volume of water and leaving Uranus on its side. Is it possible????"

(It just says "as massive as Earth" not actually Earth.)

I think this unlikely. A Mars size object (Theia) hit Earth about 4 billion years ago and produced the Moon. Presumably your collision with Uranus must have been before this. If Earth. When was this suggested to happen and where would the water have come from? Whilst there may be some water in the mantle, hydrogen, helium and methane compose the atmosphere. The heat of a major collision would have substantially reduced such atmospheric volatiles.
 
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rod

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Catastrophe, it looks like in your model, we have an Earth smack down event with Uranus that allowed Earth, perhaps the proto-earth to carry off plenty of water from Uranus. Then the proto-earth migrating inwards, parked itself into a 1 AU orbit around the Sun. Theia shows up and we have another smack down event to create the Moon.

Okay, giant impact events in new computer models for rocky type planets can create the synestia phase of matter, a new phase of hot matter not seen yet in astronomy, Planetary collisions can drop the internal pressures in planets

I see various studies now on the synestia phase from planetary impacts. It seems to me, no water would remain though.
 
Astronomers have worked out details of the giant impact that knocked Uranus so famously askew.

What smacked Uranus on its side? Something icy and as massive as Earth, scientists say. : Read more
There has been several models for Uranus system formation recently, which were not very convincing. If you have a collision your moon system will be disturbed so need more in the model to predict everything associated with Uranus. And if you have tilt changes from orbital forcing the models get max 60 - 70 degrees of tilt so need an impactor anyway [ https://aasnova.org/2020/03/10/a-new-approach-to-tilting-uranus/ ].

I thought this would be another model with explicit finetuning problems - it presumes an icy impactor - but the model results are astoundingly convincing! They can reproduce the entire architecture of the main moons in the Uranus system - moon orbit tilts, ring tilts, number of moons, moon masses, mass ordering (outer larger moons) - from simple hierarchical growth models. They also mention more detail problems they may solve.

So, some finetuning in the type of impactor, but icy ones would be typical out there. It's mass would be ~ 0.1 Earth mass or Mars massed. Like Theia.

I note two immediate problems, but also some possible solutions:

- The model implies the 5 major moons formed around a planet that did not have moons before the collision. (Or at least lost them latest at the collision.) C.f. the circumplanetary disk that Jupiter's Galilean moons seem to have originated from.

But the same applies to Earth, presumably Mars' moons and maybe Saturn's earliest moons (which moons are a mess). So that can't be a killer as much as a new mystery to solve.

- They don't explicitly explain why Uranus rotates as fast as Neptune, I think. The orbit tilt model - rightly - made a huge deal of that they expect that as the planets formed from the circumstellar disk. On the other hand a 1/100 mass impactor may not change angular momentum much apart from tilt.

Specifically here, the model gets the impactor end velocity (~20 km/s) solely from Uranus gravity acceleration. Not much external momentum delivered. (Also: likable model null constraint!)
 
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Catastrophe

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Catastrophe, it looks like in your model, we have an Earth smack down event with Uranus that allowed Earth, perhaps the proto-earth to carry off plenty of water from Uranus. Then the proto-earth migrating inwards, parked itself into a 1 AU orbit around the Sun. Theia shows up and we have another smack down event to create the Moon.

Okay, giant impact events in new computer models for rocky type planets can create the synestia phase of matter, a new phase of hot matter not seen yet in astronomy, Planetary collisions can drop the internal pressures in planets

I see various studies now on the synestia phase from planetary impacts. It seems to me, no water would remain though.
NO NO NO NO NO That is NOT my view. I think you mean Jackthehack!
 
I’m wondering if Earth could have smacked Uranus taking a large volume of water and leaving Uranus on its side. Is it possible????
That is an uninformative question in general, since very little is explicitly forbidden in physics - even "forbidden" transitions among particles happens at some (very low) frequency. So it is "possible".

More interesting is to ask if it is likely.

First, not likely in comparison with more accepted models for Uranus tilt formation, which aim to predict only that.

Second, Uranus orbits tens of Sun-Earth distances out. How did Earth go out there and back here? (Never mind the two collisions (with Uranus and with Theia) and surviving them both et cetera. Catastrophe mentions even more problems.)

But again, since it is "possible" we can always think idly on these things from time to time ... it trains our hypothesis building skills.
 
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Catastrophe

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Let me make this QUITE CLEAR.

I never suggested that Earth hit Uranus.
I would as soon suggest that Pluto hit Mercury and robbed its mantle
and I am NOT suggesting that either.
 
My observation, like Theia, this 3 earth mass object is an NOO, non-observable object and the impact event, I call a UE or unobserved event. Perhaps a UOE, an unobservable event. Here is something from the abstract, https://www.nature.com/articles/s41550-020-1049-8, "The ice-giant planet Uranus probably underwent a giant impact, given that its spin axis is tilted by 98 degrees1,2,3. That its satellite system is equally inclined and prograde suggests that it was formed as a consequence of the impact. However, the disks predicted by the impact simulations1,3,4 generally have sizes one order smaller and masses two orders larger than those of the observed system at present. Here we show, by means of a theoretical model, that the Uranian satellite formation is regulated by the evolution of the impact-generated disk. Because the vaporization temperature of water ice is low and both Uranus and the impactor are assumed to be ice-dominated, we can conclude that the impact-generated disk has mostly vaporized. We predict that the disk lost a substantial amount of water vapour mass and spread to the levels of the current system until the disk cooled down enough for ice condensation and accretion of icy particles to begin."

More NOOs and UE or UOEs used in the model. Keep *tweaking* :)
I think we agree on the models finetuning. But I do find the new model convincing. (I have said as much my initial comment.) See their image with the simulated moons and their theoretical explanation and fit to that.

For context, I like to have my concepts testable. Scientists use to describe their personal opinion of some models by using the concepts "direct" and indirect", which I never seen a testable definition of. (Akin to how laymen may suggest that 'it's just a theory' for a testable theory, 'it's an assumption' for a testable constraint and 'need a proof' for not accepting evidence, but in these cases their erroneous claims are precisely testable.) I would therefore opinionate [!] that your "non-observable object", "unobserved event. " and "unobservable event" are opinions that may or may not be arguable and/or shared.

To move to more testable ground, since these models are precisely testable I would call their method of modeling events observations in case 1) they are well tested and 2) the competing models are less likely. We are not there yet, but I don't think they are "tweaking" this model (aside from the composition of their impactor, but it is rather likely composition out there). It is very unbiased and do not even need any specific initial impactor velocity.

And even if they were still "tweaking" in some other general case, it is not a problem with the scientific method. "Tweaking" and other means of improving are strengths.

[Some context: If I see a shadow of a tree falling from behind a house, it is most likely a tree that I observe (through recognizing the shadow). Whether or not I observe the tree or its shadow, it is done by reflected light and assessing the light properties (spectral and/or image et cetera). All observations are "indirect" as far as I can see, they are measurements of properties. The other option would be that asked for property measures are somehow inserted into our databases (which is a testable but meaningless definition of "direct").]
 
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Let me make this QUITE CLEAR.

I never suggested that Earth hit Uranus.
I would as soon suggest that Pluto hit Mercury and robbed its mantle
and I am NOT suggesting that either.
'
I hope you didn't read my comment as if I think you thought that Earth hit Uranus. If you did, I wrote it poorly - I tried to point out that you mentioned how there is very little time for the complicated chain of events suggested by Jackthehack.
 
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rod

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I think we agree on the models finetuning. But I do find the new model convincing. (I have said as much my initial comment.) See their image with the simulated moons and their theoretical explanation and fit to that.

For context, I like to have my concepts testable. Scientists use to describe their personal opinion of some models by using the concepts "direct" and indirect", which I never seen a testable definition of. (Akin to how laymen may suggest that 'it's just a theory' for a testable theory, 'it's an assumption' for a testable constraint and 'need a proof' for not accepting evidence, but in these cases their erroneous claims are precisely testable.) I would therefore opinionate [!] that your "non-observable object", "unobserved event. " and "unobservable event" are opinions that may or may not be arguable and/or shared.

To move to more testable ground, since these models are precisely testable I would call their method of modeling events observations in case 1) they are well tested and 2) the competing models are less likely. We are not there yet, but I don't think they are "tweaking" this model (aside from the composition of their impactor, but it is rather likely composition out there). It is very unbiased and do not even need any specific initial impactor velocity.

And even if they were still "tweaking" in some other general case, it is not a problem with the scientific method. "Tweaking" and other means of improving are strengths.

[Some context: If I see a shadow of a tree falling from behind a house, it is most likely a tree that I observe (through recognizing the shadow). Whether or not I observe the tree or its shadow, it is done by reflected light and assessing the light properties (spectral and/or image et cetera). All observations are "indirect" as far as I can see, they are measurements of properties. The other option would be that asked for property measures are somehow inserted into our databases (which is a testable but meaningless definition of "direct").]
Interesting points Torbjorn. Today we have more than 4200 exoplanets confirmed. UOE or unobservable event, how many giant impact events have been observed among the more than 4200 exoplanets that created moons orbiting them? My answer is none. The same applies to Theia. If Theia existed, it is clearly not observable today in the solar system and neither is the giant impact event with Theia. This is not a direct observation like Galileo used to argue against the geocentric astronomy with his telescope but interpretation using various modeling assumptions.
 
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Interesting points Torbjorn. Today we have more than 4200 exoplanets confirmed. UOE or unobservable event, how many giant impact events have been observed among the more than 4200 exoplanets that created moons orbiting them? My answer is none. The same applies to Theia. If Theia existed, it is clearly not observable today in the solar system and neither is the giant impact event with Theia. This is not a direct observation like Galileo used to argue against the geocentric astronomy with his telescope but interpretation using various modeling assumptions.
I think we agree on the generals, but maybe not on impacts. We can't see exomoons yet. But we know from our system as well as other systems that collisions are ubiquitous over cosmic time scales. Pluto-Charon is a fair copy of Earth-Moon, with the same impact history creating the smaller object.

Also, Theia has now been observed on the element level [ https://www.sciencealert.com/we-may-have-finally-found-a-chunk-of-theia-buried-deep-inside-the-moon ].

**********

An aside: I just read something that you may be interested in, You have been discussing planetary disks, and unless I am mistaken how they seem depleted of material when we observe them.

I don't know if you have seen this yet, maybe there is a Space article I will get to later. It is a result from the first (they claim) integrated gravitation and magnetism effects on protoplanetary disks.

"With the aid of the "Piz Daint" supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano, these scientists have now simulated the development of the protoplanetary disk both under the influence of gravity and in the presence of a magnetic field, thereby discovering a completely new mechanism that could explain previously unexplained observations.

One such unexplained observation is that planets in our solar system today rotate much more slowly than the protoplanetary disk from which they must have once emerged. During the formation of planets, as well as of stars and black holes, enormous amounts of angular momentum must be lost, but how they lost this momentum has remained unclear. This so-called angular momentum problem is well-known in astrophysics. "Our new mechanism seems to be able to solve and explain this very general problem," says Mayer."

"The newly developed method led to surprising results concerning the interaction between GI and the magnetic field. It was shown that the spiral arms formed by gravity in the protoplanetary disk act like a dynamo, stretching and strengthening the magnetic seed. As a result, the magnetic field grows and gains strength. At the same time, this process generates much more heat in the protoplanetary disk than previously assumed. Most surprising for the researchers, however, was the fact that the dynamo seems to have a significant influence on the motion of the matter. The dynamo pushes it vigorously both inward, to accrete on the star, and outward, away from the disk. This means that the disk is evolving much faster than previous theories had suggested.

"The simulation shows that the energy generated by the interaction of the forming magnetic field with gravity acts outwards and drives a wind that throws matter out of the disk," Mayer says. This would cause 90 percent of the mass to be lost in less than a million years. "If this is true, this would be a desirable prediction, because many of the protoplanetary disks studied with telescopes that are a million years old have about 90 percent less mass than predicted by the simulations of disks formation so far," explains the astrophysicist."


[ https://phys.org/news/2020-04-simultaneous-simulation-gravitation-magnetism-protoplanetary.html ; my bold.]

So their timescales fit, their angular momentum fits, and as a plus this may be a generic outcome as the fields looks vaguely analogous to the weak zonal fields that are dynamo generated in the interstellar gas of spiral galaxy disks.

But wait! There's more! From a 2014 paper I was reminded of:

"Now researchers at MIT, Cambridge University, and elsewhere have provided the first experimental evidence that our solar system's protoplanetary disk was shaped by an intense magnetic field that drove a massive amount of gas into the sun within just a few million years. The same magnetic field may have propelled dust grains along collision courses, eventually smashing them together to form the initial seeds of terrestrial planets."

"The researchers then measured the magnetic strength of each grain, and calculated the original magnetic field in which those grains were created. Based on their calculations, the group determined that the early solar system harbored a magnetic field as strong as 5 to 54 microteslas — up to 100,000 times stronger than what exists in interstellar space today. "

""Explaining the rapid timescale in which these disks evolve — in only a few million years — has always been a big mystery," says Roger Fu, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences. "It turns out that this magnetic field is strong enough to affect the motion of gas at a large scale, in a very significant way.""

"It's unlikely that chondrules formed via electric currents, or X-wind — flash-heating events that occur close to the sun. According to theoretical models, such events can only take place within magnetic fields stronger than 100 microteslas — far greater than what Fu and his colleagues measured."

"Jerome Gattacceca, research director at the European Centre for Research and Education in Environmental Sciences, says the solar system would have looked very different today if it had not been exposed to magnetic fields. "Without this kind of mechanism, all the matter in the solar system would have ended up in the sun, and we would not be here to discuss it," says Gattacceca, who was not involved in the research. "There has to be a mechanism to prevent that. Several models exist, and this paper provides a viable mechanism, based on the existence of a significant magnetic field, to form the solar system as we know it.""

[ http://news.mit.edu/2014/strong-magnetic-field-early-solar-system-1113; my bold. ]

The model paper show an averaged field strength within a 0.3 Gauss range in their model set [figure 6], which is a 30 micro Tesla range.

Seems to fit very, very, very nicely together!
 
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rod

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Torbjorn Larsson, thanks for this new simulation information on the protoplanetary disk and magnetic field. I note "With the aid of the "Piz Daint" supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano, these scientists have now simulated the development of the protoplanetary disk both under the influence of gravity and in the presence of a magnetic field, thereby discovering a completely new mechanism that could explain previously unexplained observations."

Here is a new report on Earth's magnetic field:The existence of a magnetic field beyond 3.5 billion years ago is still up for debate, "In other words, the jury is still out on whether the Earth's magnetic field existed earlier than 3.5 billion years ago. "There is no robust evidence of a magnetic field prior to 3.5 billion years ago, and even if there was a field, it will be very difficult to find evidence for it in Jack Hills zircons," says Caue Borlina, a graduate student in MIT's Department of Earth, Atmospheric, and Planetary Sciences (EAPS). "It's an important result in the sense that we know what not to look for anymore."

Here is more, Reevaluating the evidence for a Hadean-Eoarchean dynamo, "The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown."

In my opinion, it seems the protoplanetary disk with undisclosed mass used in the simulation using a date of some 4.5 billion years ago, the new simulation can reconstruct the primordial magnetic field that formed to solve the angular momentum problem of the planets as they evolved from tiny dust grains in the disk. However, the existence of Earth's dynamo generating its magnetic field before 3.5 billion years ago as well as the existence of the magnetic field *remains unknown*. Very interesting computer simulations used in explaining the origin of the solar system that can accurately model the protoplanetary disk and magnetic field that existed many astronomical units out from the Sun, some one billion years earlier than the new report on Earth's magnetic field.
 
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Sorry for my late entrance here, and I have to admit to a large void in my knowledge of this subject, so don't be too brutal. :)

On reading about the formation of the solar system, it apparently resulted from the gravitational collapse of a fragment of a giant cloud of dust and gas, which then condensed into a disc which gave rise to everything we see now. There is this issue of angular momentum (AM) that is a bit puzzling.

I can understand the collapse under gravity, that is obvious. But where did the AM of the original fragment arise? I find it difficult to imagine it arose after formation of the disc. Indeed I presume the disc formed as a result of AM.

My imagination tells me that the original "fragment" that collapsed was hit "off-center", so to say, giving rise to a rotating collapsing cloud. And this rotation (AM) was conserved and is still driving the stuff orbiting the sun today. Is it that simple, or are other aspects in play? As frequently noted by others, a strong shock wave from a nearby Type II SN seems likely to provide enough energy for imparting such AM to a collapsing fragment, and even initiating it. And couldn't a given Type II SN condense a number of clouds in its vicinity as the ejecta is essentially spherical?

It appears from my reading that the solar system formed in a cluster of stars, and many may have been large enough so that core collapses were occurring on a fairly rapid time frame, (cosmologically-wise). That would suggest there are a number of "solar system siblings" to ours out there, of fairly similar age.

And if this is the case, one imagines that most (if not all) stellar systems were formed in much the same manner. A final issue is then regarding any cloud fragments that might condense with little or no AM, and am wondering if this is known, and what type of object would it form? A single star without a disc, perhaps.

The magnetic field issues that T mentions above regarding rapid formation of the system are very interesting, to be sure. So AM is then superimposed on the gravitational and magnetic drivers of disc formation. Sorry if I missed something in all the above.
 
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Rod, I suspect when we boil most of this stuff down, there are going to be a lot of "issues" to deal with!

I hadn't gotten to read your last post about dynamos as I was drafting mine.
 

Catastrophe

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Sorry for my late entrance here, and I have to admit to a large void in my knowledge of this subject, so don't be too brutal. :)

On reading about the formation of the solar system, it apparently resulted from the gravitational collapse of a fragment of a giant cloud of dust and gas, which then condensed into a disc which gave rise to everything we see now. There is this issue of angular momentum (AM) that is a bit puzzling.

I can understand the collapse under gravity, that is obvious. But where did the AM of the original fragment arise? I find it difficult to imagine it arose after formation of the disc. Indeed I presume the disc formed as a result of AM.

My imagination tells me that the original "fragment" that collapsed was hit "off-center", so to say, giving rise to a rotating collapsing cloud. And this rotation (AM) was conserved and is still driving the stuff orbiting the sun today. Is it that simple, or are other aspects in play? As frequently noted by others, a strong shock wave from a nearby Type II SN seems likely to provide enough energy for imparting such AM to a collapsing fragment, and even initiating it. And couldn't a given Type II SN condense a number of clouds in its vicinity as the ejecta is essentially spherical?

It appears from my reading that the solar system formed in a cluster of stars, and many may have been large enough so that core collapses were occurring on a fairly rapid time frame, (cosmologically-wise). That would suggest there are a number of "solar system siblings" to ours out there, of fairly similar age.

And if this is the case, one imagines that most (if not all) stellar systems were formed in much the same manner. A final issue is then regarding any cloud fragments that might condense with little or no AM, and am wondering if this is known, and what type of object would it form? A single star without a disc, perhaps.

The magnetic field issues that T mentions above regarding rapid formation of the system are very interesting, to be sure. So AM is then superimposed on the gravitational and magnetic drivers of disc formation. Sorry if I missed something in all the above.

There is some interesting stuff on AM here:

but I should point out that it is automatic translation from the French which, however, is also available. I am not being funny about this. There are a lot of French speakers in the world.
 
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rod

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Introducing the subject of magnetic fields and what they could do to an evolving, *protoplanetary disk* or circumstellar disk, I find various reports on NASA ADS system. Magnetic fields can create havoc in dust disks, growing into planets just like new stars forming. https://ui.adsabs.harvard.edu/abs/2016PASA...33...10T/abstract, https://ui.adsabs.harvard.edu/abs/2020IAUGA..30..130B/abstract, "Numerous numerical studies suggest that magnetic fields influence the transport of dust and gas, the disk chemistry, the migration of planetesimals within the disk, and above all the accretion of matter onto the star. In short: Magnetic fields are crucial for the evolution of planet-forming disks. First indirect comparisons of theory and observations support this picture (Flock et al. 2017); however, profound observational constraints are still pending."

The other problem I observe when reading various reports at NASA ADS, dust disks (protoplanetary, circumstellar, etc) come in a wide range of sizes, some 1-3 earth masses, others like the *protoplanetary disk HD 142527*, considered to be some 49000+ earth masses. This is critical input parameter into computer simulations. If there are magnetic fields in these disks, they likely vary widely too and what the field(s) may or may not do to the evolution of the disk or how long such magnetic fields could last before decay. At the present, I work on my home database (MS ACCESS) documenting issues like this, including disk mass reports periodically published. In the solar system ecliptic today from Mercury out to Pluto or so, we have about 447 earth masses documented in astronomy.
 
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Torbjorn Larsson, thanks for this new simulation information on the protoplanetary disk and magnetic field. I note "With the aid of the "Piz Daint" supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano, these scientists have now simulated the development of the protoplanetary disk both under the influence of gravity and in the presence of a magnetic field, thereby discovering a completely new mechanism that could explain previously unexplained observations."

Here is a new report on Earth's magnetic field:The existence of a magnetic field beyond 3.5 billion years ago is still up for debate, "In other words, the jury is still out on whether the Earth's magnetic field existed earlier than 3.5 billion years ago. "There is no robust evidence of a magnetic field prior to 3.5 billion years ago, and even if there was a field, it will be very difficult to find evidence for it in Jack Hills zircons," says Caue Borlina, a graduate student in MIT's Department of Earth, Atmospheric, and Planetary Sciences (EAPS). "It's an important result in the sense that we know what not to look for anymore."

Here is more, Reevaluating the evidence for a Hadean-Eoarchean dynamo, "The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown."

In my opinion, it seems the protoplanetary disk with undisclosed mass used in the simulation using a date of some 4.5 billion years ago, the new simulation can reconstruct the primordial magnetic field that formed to solve the angular momentum problem of the planets as they evolved from tiny dust grains in the disk. However, the existence of Earth's dynamo generating its magnetic field before 3.5 billion years ago as well as the existence of the magnetic field *remains unknown*. Very interesting computer simulations used in explaining the origin of the solar system that can accurately model the protoplanetary disk and magnetic field that existed many astronomical units out from the Sun, some one billion years earlier than the new report on Earth's magnetic field.
rod, Earth's geodynamo is a bit of a sideshow I think, but it is interesting in the context of core heat and plate tectonics. The early geodynamo or its lack thereof and how it affected the atmosphere is a tad self refuting questioning - if there was no early field it can't have been that important - and the role of magnetospheres differ between planets. In Earth case, as for Mars, the latest satellite observations imply it makes the atmosphere erode _faster_ in the current era. For Earth, the field concentrates the solar wind to the poles and creates outflow funnels for the atmosphere [ https://www.space.com/11187-earth-magnetic-field-solar-wind.html ]. Venus, Earth and Mars lies at different distances and have different strength of fields, but looses comparable flows of oxygen (say).

The Jack Hills zircons have been subducted and then incorporated as heat resistant crystals in several hundred million year younger rocks, so they are unbelievably reheated and beat up. Their original crystallization temperature in the Hadean rocks were 900 - 1,100 K [ https://en.wikipedia.org/wiki/Hadean_zircon ], the Curie temperature of magnetite is < 900 K [ https://en.wikipedia.org/wiki/Magnetite ].
 
Sorry for my late entrance here, and I have to admit to a large void in my knowledge of this subject, so don't be too brutal. :)



On reading about the formation of the solar system, it apparently resulted from the gravitational collapse of a fragment of a giant cloud of dust and gas, which then condensed into a disc which gave rise to everything we see now. There is this issue of angular momentum (AM) that is a bit puzzling.



I can understand the collapse under gravity, that is obvious. But where did the AM of the original fragment arise? I find it difficult to imagine it arose after formation of the disc. Indeed I presume the disc formed as a result of AM.



My imagination tells me that the original "fragment" that collapsed was hit "off-center", so to say, giving rise to a rotating collapsing cloud. And this rotation (AM) was conserved and is still driving the stuff orbiting the sun today. Is it that simple, or are other aspects in play? As frequently noted by others, a strong shock wave from a nearby Type II SN seems likely to provide enough energy for imparting such AM to a collapsing fragment, and even initiating it. And couldn't a given Type II SN condense a number of clouds in its vicinity as the ejecta is essentially spherical?



It appears from my reading that the solar system formed in a cluster of stars, and many may have been large enough so that core collapses were occurring on a fairly rapid time frame, (cosmologically-wise). That would suggest there are a number of "solar system siblings" to ours out there, of fairly similar age.



And if this is the case, one imagines that most (if not all) stellar systems were formed in much the same manner. A final issue is then regarding any cloud fragments that might condense with little or no AM, and am wondering if this is known, and what type of object would it form? A single star without a disc, perhaps.



The magnetic field issues that T mentions above regarding rapid formation of the system are very interesting, to be sure. So AM is then superimposed on the gravitational and magnetic drivers of disc formation. Sorry if I missed something in all the above.

Very astute.

Let me try to describe the consensus model as I have grokked it, without giving any references as of yet. This is a topic where the usual entrance points like Wikipedia aren't very comprehensible, I think.

I want to cover this in two pass, first the system formation out of a molecular cloud denser part and a second pass on the formation of such parts.

Having a denser part of a molecular cloud it will at the very least self gravitate, possibly helped by flows but not necessarily so. Physics tell us such a more or less isolated gravitational gas cloud obey the virial theorem which separate the energy into gravitational potential energy and kinetic energy. So, when a disperse cloud attracts it will have flows with momentum that impose angular momentum, and the more it contracts the more it will flow. Potential energy will be converted into kinetic energy (and heat the gas, especially in the center). Think a figure skater doing an accelerated spin simply by folding in arms and legs.

What will set the main angular momentum then is a random sum of smaller flows that will dominate and amplify (mind we are still obeying the virial theorem). Further amplification comes when the spinning cloud compactify towards a disk (and now we can let the theorem go - it is still the law but it may be easier to see how a somewhat "rigid" spinning disk works as such). And here the disk formation models such as the one that integrated gravitation and magnetism effects on protoplanetary disks I linked to in an earlier comment kicks in.

In other words, solar systems should have planetary system plane's that are randomly tilted in relation to the galactic plane. And that is what astronomers see. For instance, our solar system is tilted 60 degrees in relation to its velocity vector.

Back to the immense molecular cloud and the models of it breaking into smaller parts. That process happens canonically in three stages.

First stage is that sufficiently dense clouds will have some early denser parts that will break and form a first generation massive stars. Such stars live for a few million years and go supernova. These supernovas have been observed, e.g. in the Orion cloud.

Second stage is that the supernovas compress and tear the rest of the cloud so it will generate many more, but still fairly massive stars. They live a bit longer, but they will produce massive solar winds and eject massive gas flows into the surrounding cloud, making bubbles with compressed shells. These stars and their bubbles have also been seen.

Third stage is when the expanding and densifying shells eventually break into isolated gravitationally compactifying parts and produce the third and last generation of stars, which are much less massive and so more long lived. It is estimated that the shells make 400 - 600 stars each, which is the expected number of siblings to our Sun, i.e. stars with almost the same element composition (give or take the later fusion process).

[Note that the supernova stage for Sun's parent cloud is still debated. It was believed that the cloud part our solar system emerged from had seen one or possibly two supernovas in rapid succession seeding it with heavy elements. Recently a much more explanatory binary neutron merger seems to be the main culprit for giving us gold and what not.]

Finally, if the newborn stellar cluster is gravitationally closed it will mostly stay so, If it is open, say by having ejected much gas driven by solar processes (so the virial theorem is broken), the stars will tend to disperse due to interactions with more remote masses (gravitational tides, and what not). Since we aren't in a cluster and we can't find many siblings (aside from a few candidates), it is thought - IIRC - Sun emerged in an open, now scattered cluster rather than being ejected from a closed one. I think the speed versus the average speed of stars in the galactic disk fits. But I'm not sure.
 
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An outstanding overview, T.

Point by point:

I was going to ask you about the spin axis being random throughout the galaxy. Perfect sense. How could it be otherwise?

"...solar systems should have planetary system plane's that are randomly tilted in relation to the galactic plane. And that is what astronomers see. For instance, our solar system is tilted 60 degrees in relation to its velocity vector."

more of your post:

"First stage is that sufficiently dense clouds will have some early denser parts that will break and form a first generation massive stars. Such stars live for a few million years and go supernova."

I understand Rigel could collapse at any time, even as young as it is, as it is a blue giant (like my I.D. image was - SN1987A). In fact SN1987A rewrote the book on SNs. Rigel in SN would be make an impressive sight. Probably read a book at midnight!

A great deal of gas and dust in the OMC, and still forming. Have seen it many times with my C-11 telescope using my Televue space-walk optics!

Second stages , third stages, sounds like a very convincing story. A cascade of gas clouds and star formation.

from your post:

[Note that the supernova stage for Sun's parent cloud is still debated. It was believed that the cloud part our solar system emerged from had seen one or possibly two supernovas in rapid succession seeding it with heavy elements. Recently a much more explanatory binary neutron merger seems to be the main culprit for giving us gold and what not.]

But these elements by stage three as you note should already be seeded of higher elements from SNs as all of these clouds by now would have been "contaminated" to some extent and are involved in this cascade. I do recall the story of gold etc. produced in NS mergers, but now you have me wondering about elements from each. SN (type II) form all "stable" elements above iron, I believe. Is it well modeled as to what range of elements an NS merger is likely to generate? SN nucleosynthesize from the collapsing atmosphere of the star, i.e atoms, if I remember this correctly. How do you get nucleosynthesis from NS mergers?

So if I got the first part right, AM can be generated simply by the vectors generated in the collapsing gas cloud due to density variations, and needs no other source to continue. Some form of shock wave clearly would speed things up dramatically, but likely would evolve a disc regardless.

And the magnetic field aspect of disc formation, if I remember this correctly, is acting on polarized dust grains, driving the disc formation probably orders of magnitude faster than it would otherwise. While I understand this is more theoretical, it makes for a great model.

Much appreciated.
 
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T, let me guess on the nucleosynthesis of gold etc. from NS mergers. Pressures and energy so high that some neutrons are smashed back into quarks, gluons etc, and then can synthesize all the elements your heart desires.

If this is true, did they derive this at the LHC (etc.), or is strictly theoretical? I am big fan of the Standard Model. There is nothing like "bench data" to make a believer out of me.
 
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