[meteorite-list] Re: Mercury Meteorite Puzzle

From: colin wade <ceweed_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:50 2004
Message-ID: <002101c20081$216d7d40$02000003_at_colinwad>

Hi folks & greetings
re the pallasite Q

2 ryals worth from Qatar
from the frequency of fals /vs size , it appears to me that the majority of
impacts are smaller ( why should impacts elsewhere be different from our
observations (appart from a million reasons ))
If the majority of meteorite ejecting impacts are lighter , then the surface
layer would be the most affected
since pallasites inhabit the boundary region of larger bodies, their total
mass/ impact cross section ,would be more limited again reducing the
frequency.
If the meteor generating flux is considered uniform for our solar back yard
& after allowing for gravity differentiation by other planets & the sun , &
allowing for the probability of recognition , size of impact for meteorite
escape &,& ......does the meteorite type distribution tell us the rock
distribution of the solar system ie more mass ( or impact area ) for
chondrites form smaller bodies,?

puzzled & off to work now
allthebest
colin

----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Monday, May 20, 2002 11:51 PM
Subject: Re: [meteorite-list] Re: Mercury Meteorite Puzzle


> >>While it is still possible the parent body for the E chondrites and NWA
011
> >> may be Mercury or Venus, you can't rule out asteroids just yet either.
>
> >
> > Both of these statements are incorrect. Both Mercury and Venus are
> > differentiated bodies. Neither can be the source of "chondrites" of
any
> > kind. They could however the the source of various "achondrites".
>
> Since the planets are formed from chondritic asteroids, I don't think you
can
> rule them out just because the meteorite is a chondrite.
>
> > If people are interested in a mystery here is a big one. Pallasites are
> > generally
> > assumed to be from the core / mantle boundry.
>
> That is correct.
>
> >There are quite a few
> > pallasites
> > so their formation doesn't appear to be an unusual occurance.
>
> Actually, pallasites are on the rare side, particularly when you compare
them to the
> stony chondrites.
>
> >There are
> > also a
> > lot of irons from the core side of the boundry.
>
> In terms of number of falls, irons are also somewhate rare (but not
> as rare as pallasites), but they are common in terms of total known
weight.
>
> >There are however no, as in
> > zero, meteorites with pallasitic type olivine crystals with out an iron
> > matrix.
>
> Since the olivine crystals are only found in an iron matrix, that should
> be your first big hint. Olivine is a common mineral in stony chondrites,
though
> not in crystalline form, as you noted. Since olivine is common in the
stony chondrites,
> then you would assume that the olivine was somehow converted to
crystalline form
> when it became a pallasite.
>
> > The mantle by volume would be larger than the core of most
differentiated
> > bodies. So where are the olivine meteorites? One would think they
would be
> > at least as abundent as the pallasites. Is the pallasite theory
incorrect?
>
> My guess would be the olivine crytals came about when the chondrite layer
interacted
> with the molten iron core. Since the olivine is intermixed with the
nickel-iron, that
> implies that they were mixed together when the metal portion was in a hot
molten form,
> which futher implies the chondritic material was exposed to high
temperatures and
> probably some pressure as well. Due to the exposure to the high
temperatures,
> the olivine was converted to a crystalline form. That would explain why
you only
> see the olivine crystals only in pallasites, the boundary layer between
the
> metal core and the chondritic mantle.
>
> Ron Baalke
>
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Received on Mon 20 May 2002 10:40:08 PM PDT