[meteorite-list] Questions about accretion.

[Erik Fisler]

Field Guide to Meteors and Meteorites, Norton, Page 36.
"There are two models that could describe the interior of
a chondritic asteroid parent body.  The origional body is
accreted as it orbits in the protoplanetary disk.  The 
result is a homogeneous body with its mineral components 
evenly distributed throughout the interior.  Internal 
heating by the short-lived radioisotope Aluminum 26 
provides the energy to heat the interior from the deep core
of the body to the near surface.  Thermal metamorphism 
slowly heats the interior to a petrographic type 6 at the
core.  The heat makes its way through the body, slowly
converting various regions of the interior to different 
petrographic types from type 6 to type 3.  The result is
a layered structure something like an onion's interior,
thus, the onion  shell model."
 
enjoy,
[Erik]
 

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> Date: Sun, 5 Apr 2009 12:52:46 -0700
> From: eric at meteoritesusa.com
> To: GeoZay at aol.com; meteorite-list at meteoritecentral.com
> Subject: Re: [meteorite-list] Questions about accretion.
>
> Thanks for the responses thus far...
>
> I've studied lots of material and scientific papers on accretion, but
> still have some questions. The gravity explanation is great, but it's a
> little vague. I want to know what causes it I guess at the molecular
> level. What physical forces and interactions cause the iron to migrate
> into such a solid mass at the core?
>
> If gravity alone were the case, why is it we have H and L chondrites at
> all? Everything would be one big clump of mixed material. Has the iron
> not had a chance yet to migrate out of this layer of rock to the center
> of the asteroid? I know H and L chondrites are meteoroids that have
> broken off the parent bodies but my question is simply, had they not
> been blasted off the main body, how long would it take and in what
> manner would the iron have migrated from these layers of rock to the
> core? Iron doesn't just move through stone without some sort of catalyst
> or outside force does it? Gravity itself is not sufficient to move iron
> through a stone matrix no matter how much time passes is it? If there
> are no impacts or outside forces acting upon the body how does the iron
> loose itself from the grasp of the stone matrix to move through toward
> the core? Impacts?
>
> At the beginning of the formation of a meteoroid is it electrostatic
> attraction that causes it to get larger? At what size does it produce
> it's own gravity? Or does it? How does and asteroid become so dense? If
> asteroids are super dense, and comets are loosely bound material and
> gases, would that mean that asteroids are dead comets?
>
> Wow! I know that a lot of questions. sorry... ;)
>
> Eric
>
>
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