[meteorite-list] There are no silly questions? Wait until you have read that :-)

From: star-bits_at_comcast.net <star-bits_at_meteoritecentral.com>
Date: Tue Oct 19 16:27:50 2004
Message-ID: <101920042027.15895.417578C200013DE700003E1722007507849C9B070DD39D0E9B9C_at_comcast.net>

<1) HEDs are from Vesta.

Fine. All of them? How comes that with 50.000+ known asteroids, all HEDs
come from a single one? As far as I know, spectroscopic evidence points
to Vesta, yes - but how large is the chance that HEDs do NOT come from
Vesta.>

----No they don't all come from Vesta. The spectroscopic evidence is an indicator, not a
pedigree. It is a possibility they come from Vesta or a vesta type asteroid, but there
is no guarantee.


<2) Meteorites have been ejected towards earth by collisions between
asteroids.

Fine again. But does this mean that all meteorites result from high
speed collisions of asteroids? Isn't there a chance that some have been
sent on a trajectory towards earth simply by perturbations and chaos?>

----Probably very few are a direct result of impact. Most spend hundreds of
thousands to millions of years floating around after the impact which is a lot
of time for Jupiter, other asteroids or planets to redirect the orbit.

<3) Carbonaceous chondrites are much older than ordinary chondrites.

Ok. Once again: fine. So they must be "leftovers" from the accretion
disk, matter that hasn't formed into larger bodies. So at least they
aren't asteroid material, right?>

----What is your defination of asteroid material? A one meter diameter carbonaceous
chondrite is an asteroid just like its larger cousins. If you mean they didn't get
large enough to become altered that is not true either because there are CK
chondrites throught at least CK6.

<4) Iron meteorites originate from the core of a large and destroyed
planetoid.

Mhm. How large must this thing have been? Or let me put the question
like this: what is the minimum size for a body to be able to create a
metal core? And are those main belt asteroids the remnants of the
"planetary crust" of this planetoid?

Furthermore - there must have been at least two bodies of that size
(because planetoids do not explode, they have to collide to eject core
material into the solar system. Is this assumption right or wrong?>

----Analysis of iron meteorites show there were at least 30+ (maybe somebody
has the exact number) different differentiated bodies that produced iron
meteroites. There was not a planet that formed in the asterorid region because
gravity from Jupiter prevented it. There were many smaller planetoids. How
big an asteroid needs to be to form a core depends on its composition with
radioactive decay playing a major role in heating it up, but generally it needs
to be 400 miles diameter plus or minus.

<5) Pallasites

How did the olivine get into the nickel/iron? >

----One theory is that there is a boundrey layer at the mantle (olivine) and core (iron)
and an impact forces some of the iron up into and between the olivine crystals where
it remains until the metal cools and crystalizes. This would explain the appearance
of fragmented olivines in some pallasites.
    Another theoriy is that as the metal migrates through the mantle to the core as it
reaches the core mantle boundry it solidifies before it joins the core.

<6) Seymchan

>From pictures I have seen on the net, There are pieces of Seymchan which
are just iron, some with very sparse olivine inclusions and some with
lots of olivine. How can it be that such a variety of compositions can
be within one fall? Is the Seymchan iron in the Seymchan iron meteorites
the same iron as in the pallasites?>

----Glorieta Mountain is the same way. If you imagine a semi-merged core mantle boundry
the closer to the core the more metal you would find and the closer to the mantle the
more olivine you would find. So you have 1. all iron, 2. lots of metal some olivine,
Seymchan and Glorieta, 3. Little metal and lots of olivine, Molong and
4. No iron just large pallasitic type olivine crystals, of which there are no examples.

--
Eric Olson
ELKK Meteorites
http://www.star-bits.com

Received on Tue 19 Oct 2004 04:27:46 PM PDT