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Blob
2006-Mar-21, 10:16 PM
Two British astronomers, Paul Cresswell and Richard Nelson, will present new computer simulations of how planetary systems form.
They find that, in the early stages of planetary formation, giant protoplanets migrate inward, locked into mutual orbital resonances, towards the central star.

Their simulations show that in about 2% of cases, a lone protoplanet is ejected a great distance from the central star, thus lengthening its lifetime. But 98% of the simulations show that many of the protoplanets are locked into orbital resonances and migrate together inwards. Some may even merge with the central star.
Cresswell and Nelson thus claim that gravitational interactions within a swarm of protoplanets embedded in a disc cannot stop the inward migration of the protoplanets.
The "problem" of planetary migration still remains.

IMAGE (http://static.flickr.com/34/116021650_9b53ce78e5_o.gif) (46kb, 560 x 578 - this link will be deleted)

Their research will be published in an upcoming article in Astronomy & Astrophysics.

Abstract:
Planets form from the gaseous disc that orbits a protostar. Dust grains embedded in the disc grow through collisions, accumulating first through electrostatic forces and later by gravity. The resultant objects pass through mm-, cm-, metre-sizes etc. until planetary cores of several hundred kilometres are formed. Once beyond a critical mass (around 10 Earth masses, ME) the protoplanet begins to accrete gas on neighbouring orbits, a process that takes a few million years to form a Jupiter-sized planet.
The gaseous component of the disc remains present during this process, and the imbalance of gravitational torques interior and exterior to a protoplanetary coreís near-circular orbit result in the core migrating inwards through the disk. An object the size of Jupiterís rocky core (about 10ME), starting from Jupiterís current orbital radius in a typical disc will spiral into the central star in only a few thousands of years. Hence a mechanism is needed that can halt (or even reverse) migration to prevent the destruction of protoplanets; moreover, it must be allowed to operate at a distance from the central body.

Read more (http://www.maths.qmul.ac.uk/postgraduate/anncook/cresswell04.pdf) (PDF)

Blob
2006-Mar-21, 10:33 PM
Hum,
now on the Astronomy & Astrophysics website...

The locked migration of giant protoplanets:
Press release (http://www.edpsciences.org/journal/index.cfm?edpsname=aa&niv1=others&niv2=press_release&niv3=PRaa200607)

01101001
2006-Mar-21, 11:14 PM
The "problem" of planetary migration still remains.

Are the quotes because the problem appears to be that their model doesn't reflect reality?

Edit: Oh, the quoted text is sort of from the press release The locked migration of giant protoplanets (http://www.edpsciences.org/journal/index.cfm?edpsname=aa&niv1=others&niv2=press_release&niv3=PRaa200607):


The “problem” of migration remains and requires more investigation, although the astronomers propose several possible solutions. One may be that several generations of planets form and that only the ones that form as the disc dissipates survive the formation process. This may make it harder to form gas giants, as the disc is depleted of the material from which gas giant planets form. (Gas giant formation may still be possible though, if enough gas lies outside the planets’ orbits, since new material may sweep inward to be accreted by the forming planet). Another solution might be related to the physical properties of the protoplanetary disc. In their simulations, the astronomers assumed that the protoplanetary disc is smooth and non-turbulent, but of course this might not be the case. Large parts of the disc could be more turbulent (as a consequence of instabilities caused by magnetic fields), which may prevent inward migration over long time periods.

That says a little more clearly that the problem is likely theirs and not reality's.

Blob
2006-Mar-22, 12:31 AM
Hum,
The Earth and the other terrestrial planets are the problem; they should have been swallowed up by Neptune sized protoplanets as they fell in towards the Sun.

i personally would go with the idea that the planets were the last generations of planets formed.
But it's a simplified simulation that, as they imply, didn't account for turbulence due to the proto Star and the influence of the star forming region it was born in.

Fr. Wayne
2006-Mar-22, 03:32 AM
What mechanism besides gravity could draw together a Neptune or any gas giant? Solids could bump and grind there way into bigger rocks, but gas would need not only a "long stable period" to "gell" but a trigger particle or magnetic field I would guess.

Ara Pacis
2006-Mar-22, 04:34 AM
I was under the impression that gas giants were simply terrestrials get got so big that they started holding more and more gas.

Fraser
2006-Mar-22, 05:11 AM
SUMMARY: Astronomers think they've got a handle on many aspects of planetary formation. But two British researchers have discovered a problem with the formation of gas giant planets. Under their model, the cores of these massive planets should be drawn inward by their parent star in only 100,000 years - not nearly enough time to form into a stable orbit. It could be that the first generations of planets never get past the "clump" stage before they're destroyed. It's only the later generations that actually survive long enough to become planets.

View full article (http://www.universetoday.com/am/publish/giant_protoplanet_mig.html)
What do you think about this story? post your comments below.

antoniseb
2006-Mar-22, 01:11 PM
This study seems to be looking at the build up of a giant planet from nothing. I think they should consider the situation where the giant planet starts as a second starless core that loses the race to accumulate material in the star forming process, and then has too much mass to spiral in to the star that won the race.

jlhredshift
2006-Mar-22, 01:48 PM
It very difficult for any computer simulation to embrace the full scope of the chaos of a planetary formation scenario. What role would passing stars, blackholes, or dark matter have. There are other simulations that suggest that large planets form close in and migrate out to more distant orbits. As we have discovered with every new body we examine every formation situtation will be different providing us with an endless list of formation scenarioes.

As to planetary migration, in or out, was Velikovsky right or is he still "gloriously wrong"?:wall:

mantiss
2006-Mar-22, 02:10 PM
As to planetary migration, in or out, was Velikovsky right or is he still "gloriously wrong"?

He's still gloriously wrong, sorry. :boohoo:

jlhredshift
2006-Mar-22, 02:50 PM
He's still gloriously wrong, sorry. :boohoo:

An open mind is a terrible thing to waste, don't be sorry.

Now, back to being serious, the chaotic nature of any forming system will be sure to include more degrees of freedom than current computational power allows. The history of our system shows strong interaction between major extant bodies of the time on all the planets and smaller bodies we've studied. The theory of our own moon's formation, the rotation of Venus, that Mercury could be the remaining core of a larger body, the tilt of Uranus, and the list goes on. This history, whatever it may entail, will be specific to here. Others, obviously, will be specifically different, but I feel that it is apparent that collisional attributes will factor in to the development of all systems, on a major scale, due to the migration of large mass within that system. I will also point out that the collisional nature that we see indicates regular baryonic matter and not dark matter.

Things change, they always do. "And what if Galooka thought the Yulles were to ugly to save":lol:

Smitty
2006-Mar-22, 03:50 PM
What critical differences are thought to exist between earlier and later protoplanets which support current notions that later protoplanets would be more likely to survive to become planets?

baric
2006-Mar-22, 04:05 PM
I agree with previous posters that this "problem" exists only in our computer simulations. Observationally, we are finding many systems with large planets in stable orbits at a great distance from their stars.

antoniseb
2006-Mar-22, 04:07 PM
What critical differences are thought to exist between earlier and later protoplanets which support current notions that later protoplanets would be more likely to survive to become planets?

There's less stuff in the protoplanetary disk to be able to exchange momentum with the big planet.

antoniseb
2006-Mar-22, 04:11 PM
I have merged this thread with the parallel thread in the Astronomy section.

Gerald Lukaniuk
2006-Mar-23, 12:18 AM
Why should they be destroyed? What the model seems to omit is that there is more at work in planetary formation than gravity. What to say when a giant rocky protoplanet smashes into a star a significant portion of it isn't blasted out like water drops on a hot griddle to form small rocky planets in close orbits as in our solar system.

Fr. Wayne
2006-Mar-23, 06:38 AM
I'm glad I don't research methane giants.

Jerry
2006-Mar-23, 02:41 PM
I agree with previous posters that this "problem" exists only in our computer simulations. Observationally, we are finding many systems with large planets in stable orbits at a great distance from their stars.
There is another problem emerging: We are seeing heavy metal distribution in the comets we analysis, and also in the Saturn system that is much higher than anticipated by the classic dust condensation model. One reason put forward, is that much more matter has been redistributed via the solar wind and inner solar system collisions. It could be the basic model that is flawed, and not the simulations.

George
2006-Mar-23, 07:49 PM
Is it generally believed many protoplanets get swallowed?

But in most cases (98%), many of the protoplanets are trapped into a series of orbital resonances and migrate inward in lockstep, sometimes even merging with the central star.What happens when a proto Jupiter-class planet slams a protostar?

------

Several months ago, I remember reading about hot regions and turbulence expected from a given model.

Large parts of the disc could be more turbulent (as a consequence of instabilities caused by magnetic fields), which may prevent inward migration over long time periods.
Has Spitzer been able to address internal disk dynamics much?

Gerald Lukaniuk
2006-Mar-23, 08:34 PM
He's still gloriously wrong, sorry. :boohoo:
All lot of rare conditions would have to be met for two passing stars to exchange a planet. Their poles would need to be parallel. So that their planetary disks align. The planet would have to be precisely between them in such away its momentum is tranferred to a path around the other planet since the net gravitational force of its new home would be only slighly larger than the old at that moment. If Gn were too strong the planet would fall into new. as would both stars outer planets into the other star. That moment there would be peak 2x normal stellar radiation assuming the luminance of the stars verses the inverse square of the planet's distance was the same. Then the planet could remain in a safe orbit and life that had evolved at that level of luminance could survive if it could handle the heatwave and tidal disruptions. It would be a very narrow window of opportunity and unless there was something else synchronizing and aligning the poles stars in a cluster like planets in a solar system it would be an enormously rare. But its a big unverse and what the hell somebody wins the lottery.

cress
2006-Mar-24, 01:42 AM
Hello all. Can you guess from my name who I am? It's late at night, I'm meant to be working, I stop for a quick browse and, to my surprise, follow a trail of links here. Should I take it as an insult that this first appeared in the 'Bad Astronomy' section, or a compliment that it was moved here? ;)

There seems to be a little confusion as to what was being said in the paper. Modern planetary formation and migration theory is still pretty new, there's not much written about it yet, so let me lend a hand to your debate. I was a bit unsure if it's really ethical for me to say anything at all, but I guess posting to the second non-sticky thread down isn't really much of a bump :think:

As some of you have pointed out, the problem is theoretical, not physical. Thirty years ago a very clever guy realised that planets in smooth discs (pretty much the only sort of disc, back then) should migrate. Lots of other clever people worked on more theory and simulations, but to everyone's annoyance, he was right. :p

So when we say there is a "problem" of planetary migration, we mean that all the theory we - as in, all astronomers - have predicts it, but clearly it doesn't happen or else something is stopping it (at least, some of the time). I say clearly, because we are sat on a planet orbiting a star. That's the sort of evidence I don't like to argue with. :)

The paper set out to test one possible theory of stopping it. It didn't work. We didn't expect it to. But it needed testing, nontheless. Personally, I found the copious production of resonant and co-orbital systems a much more interesting though unexpected outcome. I should probably stress that more in future.

And for my money, the more common answer is turbulence, not 'last generation' planets, Blob. But it's probable that both happen, in different systems. Maybe even a combination of the two. And I am biased, of course!

Oh, and before some wag asks if it's really me, there will be a story about this on Space.com sometime soon. The writer will be Ker Than. Hopefully that will be proof enough.

Goodnight, all!

antoniseb
2006-Mar-24, 01:53 AM
I was a bit unsure if it's really ethical for me to say anything at all

You are most welcome to participate. This is discussion not debate. If you're up to answering questions, there will be many. Some mainstream, some from Alternative ideas, and some from untrained hobbyists. You can choose to answer none, some, or all, or just make comments as you see fit.

cress
2006-Mar-24, 02:22 AM
Well, I just meant that I didn't want to come across as if I was only here to pimp my own stuff. To be honest I'm a bit bewildered at 'all' the attention (which is a lot for a theorist!). And I have no intention of coming here regularly - time just doesn't allow. But I'm happy enough to pop by every now and then and answer a few questions - knowledge and education should be open and accessible to all, not something for researchers to hide away for their own private entertainment. Just don't swamp me with them all at once, eh? :naughty:

antoniseb
2006-Mar-24, 02:56 AM
I'm happy enough to pop by every now and then and answer a few questions

How about my question concerning larger planets (such as Jupiter) forming as co-developing starless cores, until the winning core takes over. This could explain why the Jupiter isotope and element ratios more closely match the intersteller media, and solar values than do the inner planets. It also might explain why Jupiter didn't spiral all the way in.

Also, tell me more about this turbulence explanation.

cress
2006-Mar-24, 11:11 AM
This study seems to be looking at the build up of a giant planet from nothing. I think they should consider the situation where the giant planet starts as a second starless core that loses the race to accumulate material in the star forming process, and then has too much mass to spiral in to the star that won the race.
Well, you're describing a brown dwarf binary. That's certainly plausible. But most of us (at least in the circles I frequent) believe that planets form by first building up a rocky core, and then capturing the surrounding gas. To form something out a 'clump' of gas, you need a very cold and massive disc, much more so than the ones we appear to be seeing planets form in. Personally I would expect a disc that massive to produce a brown dwarf, rather than a planet, but the dividing line between the two is blurry at best. But I don't think it would be too hasty to rule it out for the sytems of super-terrestrial cores I considered here. Of course, brown dwarves are quite common too. But whether you'd consider them a super-planet or a failed star, you'd need to assess on a case-by-case basis, at least for now.

Turbulence, as far as the planet goes, is just when the reaction on the planet from the disc is swamped out by natural fluctuations in the disc. It's still a pretty new idea, as these things go. A very crude analogy, but:

Imagine the planet as a rowing boat on an ocean. When the sea is calm, the oarsmen can row away to their hearts' content and be sure to get where they want, even with a small underlying drift. (In a disc, the drift would be in the same direction anyway.)
Now imagine the sea is choppy, with huge waves washing over the boat. It doesn't matter how hard they row, the effect they're having is negligible compared to how the sea is throwing them around. They might sit more or less still, or they might be sent huge distances one way, then another. It's stochastic.
The middle ground (or fluid, if you prefer) is when the waves are comparable to our sailors' strength. They might still get knocked around, but if you watched them for long enough you'd see they were making slow progress in the right direction. That's the sort of turbulence we might see. But we really need better observations and models.

Of course, by 'rowing' I really mean an angular momentum exchange with the disc; nothing so simple as exerting a straight force on the fluid. But hopefully it gets the idea across.

And, uh, please don't take anything I say in the forum as gospel. This is all for your entertainment here, it shouldn't be quoted or used anywhere else. There will be times when I'm hopelessly wrong. I'm still learning too (if I wasn't, I wouldn't be doing my job properly).

antoniseb
2006-Mar-24, 01:29 PM
Well, you're describing a brown dwarf binary.

Thanks cress. I liked the rowing analogy. Concerning the brown dwarf binary business, I think that's a realistic possibility to explain Jupiter and perhaps Saturn. The difficulty using the term 'brown dwarf' in this case is that it usually connotes an object in the 30 to 80 Jupiter mass range, but the process that would create a brown dwarf could well also work for much smaller objects. I don't know what the limiting case would be, but certainly Jupiter could have formed this way, predating the protoplanetary disk.

I'd be interested in knowing how the model would work with Jupiter preformed at 90% of its current mass before the disk is created.

George
2006-Mar-24, 05:47 PM
Welcome, cress. Delighted you're here.


A very crude analogy, but:
Imagine the planet as a rowing boat on an ocean. When the sea is calm, the oarsmen can row away to their hearts' content and be sure to get where they want, even with a small underlying drift. (In a disc, the drift would be in the same direction anyway.)
Now imagine the sea is choppy, with huge waves washing over the boat. It doesn't matter how hard they row, the effect they're having is negligible compared to how the sea is throwing them around. They might sit more or less still, or they might be sent huge distances one way, then another. It's stochastic.
The middle ground (or fluid, if you prefer) is when the waves are comparable to our sailors' strength. They might still get knocked around, but if you watched them for long enough you'd see they were making slow progress in the right direction. That's the sort of turbulence we might see. But we really need better observations and models.

Of course, by 'rowing' I really mean an angular momentum exchange with the disc; nothing so simple as exerting a straight force on the fluid. But hopefully it gets the idea across.
Nice analogy. Would blowing hard rain be allowable in the analgoy as a 3rd dimensional force [cloud collapse along z axis]? :)

Also, could T-Tauri tantrums contribute to turbulence in their disks?


And, uh, please don't take anything I say in the forum as gospel. This is all for your entertainment here, it shouldn't be quoted or used anywhere else. There will be times when I'm hopelessly wrong. I'm still learning too (if I wasn't, I wouldn't be doing my job properly).
Yes. Otherwise, they'd had tossed me a long time ago. :) [I am only an amateur.]

cress
2006-Mar-24, 11:52 PM
Glad you liked the analogy. Been waiting to try that one out. :)

antoniseb: Brown dwarves - I don't really think so. It's an idea, but there are a number of problems. Off the top of my head:
1) Earth and friends are there already. So you're already needing core accretion to explain them anyway. Why two mechanisms?
2) The accretion disc had a definite centre, because everything (big) we see now is in nice circular-ish orbits. So either
a) Jupiter was originally formed at the centre, near the Sun, but was flung outwards, which requires anomalous differential accretion rates between the two, or a third body we longer see today; or
b) You have to explain some fairly pecular orbital dynamics to get everything looking nice and tidy today
3) Even if Jupiter formed roughly where it is, you still have to explain Neptune and Uranus, which have nowhere near enough material for a gaseous core collapse model. If they can manage solid accretion processes, J and S certainly can.
4) The Sun doesn't appear large enough for the disc to have been suffiently massive to support a core collapse anyway. Like I said, cold and massive - very massive.

That said, you should know the lowest limit for a BD that most people won't argue over is only 13M_Jup (which is when deuterium burning begins). Free floating 'planets' below that limit are a separate classification problem, as are large bodies around other dwarf stars, where the mass of the 'planet' is comparable to that of the star, even if it's below the burning limit.

Some people have suggested we call things below the limit planets/BDs depending on whether they formed by solid accretion or gasous collapse. It's an idea I like personally, but since it's hard often hard to tell even that much about we see - made even worse when you consider collapsed bodies can then collect a solid core afterwards, so the two are probably indistinguishable - it doesn't really move us on very far.

Putting Jupiter in the simulations - it's been tried. Not with a true hydrodynamic model like I used here, but with a few analytical approximations. I know of at least two groups who get very different results. One excellent paper found that a Jupiter can act as a 'safety net', by catching smaller, migrating planets in resonance (similar to how my planets all ended up in resonances, I suppose. It seems quite common). In truth, I expect it to be quite sensitive to the relative migration rates, and planet and discs masses. But it may well work a lot of the time.

cress
2006-Mar-24, 11:59 PM
And another:

Also, could T-Tauri tantrums contribute to turbulence in their disks?

In the portion of the disc nearest to the star, sure. I'd be quite surprised if they didn't - for turbulence, you're relying on the magnetic fields, and that's the strongest source of them.

Farther out though... depends what you mean by a 'tantrum'. It's most likely all serious turbulence is derived from magnetic fields, which should get locked into the star pretty early on in the collapse. So in that sense, the star is responsible for maintaining the field throughout the disc.

I don't think you could rely on the occasional 'storm' to keep the fields sufficently elevated and/or penetrating (above the usual level, whatever that turns out to be) farther out in the disc, though.

George
2006-Mar-25, 09:22 PM
Thanks. I had been reading a little on the tachocline (http://www.atm.damtp.cam.ac.uk/people/mem/papers/SQBO/solarfigure.html)and a little on T-Tauris. If the solar regions below the tachocline rotate as a solid and above differentially, a protostar might be tempermental enough to heat up the inner disc as it settles in. T-Tauri's do exhibit "tantrums". [I was just curious if this helped in some way with your picture.]

Fr. Wayne
2006-Mar-27, 10:46 PM
Has the disintegration of other companion star(s) off the table in this discussion, since we have 4 gas planets of proportional distance based on their metal content?