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borman
2008-Nov-07, 01:29 AM
Do comets come from planets?

There seems to be some evidence and new theories that may have a bearing on the question.

Press releases:
Meteorites’ magnetism holds clues to planet birth

http://astronomynow.com/081105meteoritesmagnetismholdscluestoplanetbirth.h tml

Dwarf planet's body parts litter outer solar system
http://space.newscientist.com/article/dn14954-dwarf-planets-body-parts-litter-outer-solar-system.html
ICARUS paper abstracts:
Stardust findings favor not only the planetary origin of comets but the underlying close-binary cosmogony of the Solar System as well

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4S9G97H-1&_user=10&_coverDate=09%2F30%2F2008&_rdoc=18&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236821%232008%23998029998%23696420%23F LA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=32&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=19f47a0356f37c54a89cce258ee34e33

The formation of the Oort cloud in open cluster environments

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4S7BDJF-2&_user=10&_coverDate=09%2F30%2F2008&_rdoc=20&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236821%232008%23998029998%23696420%23F LA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=32&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4f0df4f2797342bec04a40c90ad6600e

Origin of three-dimensional shapes of chondrules I. Hydrodynamics simulations of rotating droplet exposed to high-velocity rarefied gas flow
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4SJG6BR-6&_user=10&_coverDate=09%2F30%2F2008&_rdoc=24&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236821%232008%23998029998%23696420%23F LA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=32&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5e47e3d9bce11aa1268b495ee9841756

timb
2008-Nov-07, 03:39 AM
No.

triclon
2008-Nov-09, 04:26 AM
Comets come from the outer solar system and are presumed to have formed out there in the cold depths beyond Neptune from the remains of the solar nebula that created the sun and the rest of the solar system. Most comets have orbits which lead beyond Neptune. Plus how are planets supposed to cough up comets? Nobody has ever seen a comet pop out of a planet before.

timb
2008-Nov-09, 04:51 AM
I think the idea is that there is a planet way "out there", let's call it Uribin, that somehow fires comets at us as a result of huge explosions on its surface. If that were true then there should be plenty of unbound comets observed, but there aren't. Exactly how Uribin sustains a series of massive explosions over billions of years I don't know and don't care to be informed.

cran
2008-Nov-09, 02:42 PM
Do comets come from planets?

Perhaps the question wasn't worded in the best way - hence the derisory replies ...

I believe there are a number of papers, articles, etc regarding short-period comets and their relationship with the Kuiper Belt ...

I believe there are also a number of studies of planetary formation, which include the concept (supported by observations) that protoplanetary objects, etc, have been struck sufficiently to separate all or part of the pre-impact mass ... and that some of the resulting debris has accreted onto other forming objects ... and some has remained in variously eccentric orbits ...

I believe that Kuiper Belt Objects are not classed as planets per se ...

borman
2008-Nov-09, 11:43 PM
Comets come from the outer solar system and are presumed to have formed out there in the cold depths beyond Neptune from the remains of the solar nebula that created the sun and the rest of the solar system. Most comets have orbits which lead beyond Neptune. Plus how are planets supposed to cough up comets? Nobody has ever seen a comet pop out of a planet before.

The essential question is that of presumption or a priori assumptions made about how comets formed. According to some theories that have been around for some time, it is thought that comets formed directly from primordial materials and did not go through a phase where the ices first accumulated into a planetismal that may have undergone differentiation upon reaching a radius of 160 km only to crash into another planetismal and have various parts scattered about. The presence of magnetic fields in some small leftover parts only favors but does not yet prove the later. But the former, while being around for a longer time, is still an untested hypothesis nevertheless. The longevity of a speculation does not prove it is right.

One way to get some ground truth to test the various speculations, regardless of how long they have been around or well they have have been received, is to send a mission to a comet and bring back samples to finally begin to test which, if any, of the theories can pass reality tests. This is why such missions are undertaken; they are to test the theories.

So far, the initial results appear to challenge the viability of the older theories that were around longer and were, up to now, thought to be the leading concordance theory. Of course, others will be given the opportunity to independently confirm the initial findings using the same data returned by the experiment.

For example, even a short lived internal magnetic field in a small planetismal will do better than gravity alone in attracting and sweeping out its area of ices if the metals in those cores can be attracted by magnetism. The EM force is some 39 orders stronger than gravity.

borman
2008-Nov-09, 11:56 PM
Perhaps the question wasn't worded in the best way - hence the derisory replies ...

I believe there are a number of papers, articles, etc regarding short-period comets and their relationship with the Kuiper Belt ...

I believe there are also a number of studies of planetary formation, which include the concept (supported by observations) that protoplanetary objects, etc, have been struck sufficiently to separate all or part of the pre-impact mass ... and that some of the resulting debris has accreted onto other forming objects ... and some has remained in variously eccentric orbits ...

I believe that Kuiper Belt Objects are not classed as planets per se ...


Since there seems to be heated debate about what a planet is or is not, it is probably better to avoid diverting into this problem and sort the problem into whether comets come from undifferentiated growth from icy kernals and have remained so from primordial times or whether they were derived from collisions between bodies that may have differentiated before collision and so represent an icy leftover piece of a more complex object.

The subtle chemical differences between the two ideas would need to be tested in the lab after acquiring a piece of a comet.

cran
2008-Nov-10, 02:04 AM
Since there seems to be heated debate about what a planet is or is not, it is probably better to avoid diverting into this problem and sort the problem into whether comets come from undifferentiated growth from icy kernals and have remained so from primordial times or whether they were derived from collisions between bodies that may have differentiated before collision and so represent an icy leftover piece of a more complex object.

The subtle chemical differences between the two ideas would need to be tested in the lab after acquiring a piece of a comet.
there is a danger with drawing conclusions based on a single sample -
if all meteoroids were defined in this way, we'd be wrong ...
if all life on Earth were defined by what we find on the surface, we'd be wrong ...
so why presume a single source/definition for comets?

borman
2008-Nov-10, 02:34 AM
Most tests are not done to try to prove a theory right, but rather to falsify a theory or an aspect of a theory. The only data we have is from the one comet particle gathering mission.

What appears to be case is that we have the counter-example that falsified any universal notion that the concordance theory as regards solar system evolution with respect to comets. While it is true that it is only from one comet, it is also apparently true that this comet represents a counter-example to the prevailing theory. How many counter-examples are needed to falsify a theory?

cjameshuff
2008-Nov-10, 03:32 AM
For example, even a short lived internal magnetic field in a small planetismal will do better than gravity alone in attracting and sweeping out its area of ices if the metals in those cores can be attracted by magnetism. The EM force is some 39 orders stronger than gravity.

Magnetism is a dipole field, falling off with the cube of distance, and the magnetic fields of individual magnetized particles embedded in an accreting iceball will tend to largely cancel each other out on the scale of the object as a whole. Electrostatic charges will quickly neutralize. Gravity, on the other hand, always adds.

Comets have a large portion of their volatile elements remaining. They may incorporate magnetized dust blown out from the inner system, but it is clear they were not hot enough to be partially liquid, long enough to have a magnetic field that affected their accretion. In addition, they come from the outer system...the sheer volume of space and sparseness of matter means that collisions won't happen as often as they did in the inner system.

Look at Earth and its magnetic field...a big spinning and convecting core that's been largely liquid for billions of years. Earth's magnetic field is stronger for its mass than that of any other object in the solar system (disregarding artificial objects and the occasional magnetized iron dust particle). And yet...it's the gravitational force of its mass that dominates, to such a degree that we rarely even have to think about the magnetic field.

cran
2008-Nov-10, 04:12 AM
Most tests are not done to try to prove a theory right, but rather to falsify a theory or an aspect of a theory. The only data we have is from the one comet particle gathering mission.

What appears to be case is that we have the counter-example that falsified any universal notion that the concordance theory as regards solar system evolution with respect to comets. While it is true that it is only from one comet, it is also apparently true that this comet represents a counter-example to the prevailing theory. How many counter-examples are needed to falsify a theory?
the bold bit seems to be an incomplete statement - "any universal notion that the concordance theory [what?] as regards ..." etc please supply the appropriate verb ...

I wasn't aware that there was a prevailing theory which requires a single source of material for comets - seems a bit silly when the short-period and long-period comets were thought to originate in different parts of the solar system (I've lost count of how many) years ago ...


... and sort the problem into whether comets come from undifferentiated growth from icy kernals and have remained so from primordial times or whether they were derived from collisions between bodies that may have differentiated before collision and so represent an icy leftover piece of a more complex object.
the whole "either/or" concept is the problem I have here -

what happens to the "or" theory when it turns out that some comets are one type, and some comets are the other?

PraedSt
2008-Nov-10, 07:07 AM
The EM force is some 39 orders stronger than gravity.


...falling off with the cube of distance...Electrostatic charges will quickly neutralize. Gravity, on the other hand, always adds...

Why do so many here, there, and in ATM, have problems with this? :confused:

(Meant kindly, Borman, I enjoy your posts. Just curious...)