Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
TomC10
sage
Reged: 12/21/04
Posts: 239
Loc: Land of Enchantment
|
|
This began as a response to Dane_B's post on orbital motion. I didn't want to hi-jack his thread.
wrt the accepted theory of accretion from gas and dust..
I recently read a paper that investigated the possibility that gas giant planets may be stunted siblings of their stellar companions. i.e. that they did not actually begin in the protoplanetary disk but in the original stellar nebula. They are then captured by their larger, main sequence sibling. This challenges the assumption that planet formation begins around the "parent" star.
There are admitted problems with the accretion theories for both gas giants and terrestrial planets.
I've wondered about the following for a couple years now; Despite the extremely high pressures and temperatures that pre-supernova stellar material experiences. And the fact that the escape from stellar gravitational confinement would drive this plasma to expand into the vacuum..("vaporize"?) could large chunks of this (probably iron) material stay together or coalesce after the explosion? Neutron star remnants of course retain the gravitational confinement that holds them together. However the lateral kick they often get shows there are non-symmetries in the explosion or material distribution. So a perfect vaporization of all remaining material may be too simplistic. There is more going on.
Basically I've been wondering if large "chunks" (not gas or dust) of refractory material could exist in stellar nebula before stars begin to form? Actually this doesn't sound unreasonable at all. These chunks would be swept up in star formation along with the gas and dust to become part of the protostellar and protoplanetary disk. However, the existence of pre-coalesced chunks or "cores" would significantly change and accelerate the process of planet formation.
This implies that the cores of planets (say.. Earth, Mercury, Venus, etc...) may have existed before the sun began to form. Dating of radioactive material has been used to calculate ages of solar system material, but I wonder if material buried in the molten cores of planets could be of a different age.
Additionally, previous generations of stars (not the first generation of course) must have had planets, and analogs of our Kuiper and Oort Cloud objects that were not totally vaporized during supernova events. Where did these objects go? Frankly, the picture of a messy non-homogeneous mix of gas, dust, and assorted masses in stellar nebulae seems more realistic than the tabula rasa assumption of pure gas and dust.
--------------------
------
Tom C
C10 NGT
|
Pess
(Title)
Reged: 09/12/07
Posts: 1910
Loc: Toledo, Ohio
|
|
I had a wise professor who once said the answer to all such questions was 'yes', 'no' and 'maybe'.
Although it seems obvious now there was much perplexity until recently about bright blue, meaning 'young', suns appearing in many ancient nebulas.
The dilemma was how could these million year old infants still be forming in these billion year old nebulas?
This head scratcher was resolved when it became apparent that older stars had combined recently under gravitational influence or disturbance and formed the hot new blue stars typical of young nebulae.
Stuff in solar systems is getting flung in and out all the time by passing star masses. Local supernova can certainly send disruptive shockwaves through densely packed systems.
It wouldn't be too hard to envision an ancient swarm of metallic rocks the size of mars getting flung on a trajectory through a large brand new nebula and forming the gravitational 'seedlings' of future stars and planets.
Some recent papers have even suggested that certain types of Supernovae can explode repeatedly in a sort of lopsided manner. No reason rather large chunks couldn't be shotgunned out. Of course the larger the piece the less the ejected pressure was and the more likely it'll return to the 'mother' so to speak rendering it unavailable to form mantle material in new systems.
Heck, one of our Voyager spacecraft could, in a few billion years, wander through some dense gas and be just the trigger to start clumping stuff.
Pesse (We'll name the eventual new star V'ger.) Mist
|
llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
|
|
I'm a little doubtful about fragments of stellar plasma condensing to "large" solid bodies in the absence of an accretion environment. But then, I don't know enough to understand the calculations or assumptions required, either.
I like visualizing the idea of millions of orphaned KBO's careening through a dusty nebula, and later getting snapped up by a newly-forming star. I'm sure that happens occasionally, whether it's common -- again I don't have any knowledge or intuition to contribute here.
--------------------
"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
|
matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10022
Loc: Chaville, France
|
|
I believe the idea of matter/gravitational "seeds" from which larger objects form.
It does not mean that's the rule - it means it's one of several ways Nature can cook up large bodies.
And there is little way of knowing after that whether a planet/star comes from one of these "seeds" or is born ex-nihilo, accretion style.
However, the signature of accretion-produced planetary systems is that planets are expected to be all in an "ecliptic" plane around their star - so you would expect the "seeded" planet to be outside that plane and it would be a hint. And such a planet might have disturbing, even fatal, effects on a protoplanetary disk.
--------------------
Matt
CI700 mount with various scopes on top.
|
jupiterzkool
Pooh-Bah
Reged: 05/08/06
Posts: 1341
Loc: Pasadena, CA
|
|
I am also skeptical about stellar plasma "condensing" or even causing "condensation" to occur. However, the "absorbing" of existing solid bodies into the proto-planetary nebula does not sound to off the wall to me.
-S
--------------------
Scott G. Edgington, Planetary Scientist
Cassini-Huygens: Mission to Saturn & Titan
Yes, Asia, John Wetton Fan
|
TomC10
sage
Reged: 12/21/04
Posts: 239
Loc: Land of Enchantment
|
|
I had not thought through the extent of ejected bodies (jetsom?) during planetary system formation. Shostak argued that the "bullets" Jupiter supposedly protects us from were of its own making. That Jupiter basically threw a lot of matter out into the Kuiper/Oort matter reservoirs during the formation of the solar system. Icy KBO "seeds" beyond the snow line would probably be as effective as any for starting Neptune like planets.
Making the case for remnant pieces of iron after a supernova has been the most speculative part of this idea. I know researchers are trying to figure out velocities and elemental compositions of the expanding layers of supernova matter from spectra. It would be interesting to find out if interior layers of the expanding cloud have significantly lower velocities than outer layers. This along with shocks in the inner cloud might keep the iron particles in closer proximity afterwards and lead to fairly 'rapid' re-association of the particles as they cool. Iron would make a very stable seed with a large mass to surface area ratio, and less likely to dissipate from radiation - which drives the fixation on iron.
Excellent point on orbital planes. It would be a great test. One paper I read did a rough calculation on how many passes through an accretion disk it would take to change the orbital plane of a planetesimal skewed to the disk (density/velocity dependent). I'm going to start watching for mention of protoplanetary disk shapes and planarity. There should be a signature visible for a period of time if a seed were to randomly fall into a disk. I believe there is a fair amount of observational data on this already. And yes, this is just one hypothetical way planets *might* start. The idea that planets must always start from pure dust and gas just kept nagging at me as too simple.
an example of the benefits from collaborating on an idea ... thanks! 
--------------------
------
Tom C
C10 NGT
|
llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
|
|
Well, if it'll make you feel any better, the dust itself is hardly "pure".
--------------------
"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
|
TomC10
sage
Reged: 12/21/04
Posts: 239
Loc: Land of Enchantment
|
|
Hmmm, I wonder how the dust in stellar nebulae would rate against Phoenix smog on a summer day? Just imagine an entire nebula of Phoenix or L.A. smog...
CN is quite a forum. Where else will you find a Cassini planetary scientist just when you need one? Thanks Scott. I guess congratulations are in order for the 2 year mission extension? Like the Rovers, when you've got something thats working so well make the most of it.
--------------------
------
Tom C
C10 NGT
|
|
1 registered and 1 anonymous users are browsing this forum.
Moderator: llanitedave
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 212
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 