Dear Al and Bernhard,
It's true that, beside the 12 distinct chemical groups, we have about 80 ungrouped
iron meteorites which - following the existing models of asteroid formation and
differentiation ("core formation") - must be derived from 80 different parent bodies
(PBs).
As Gero Kurat (Naturhistorisches Museum Wien) has pointed out in a recent paper (see
ref below), this is quite strange, as there are only a "hand full" of parent bodies
known for stony and stony-iron meteorites. He, therefore, has come up with a very
interesting - and I think striking - alternative explanation for the formation of the
PBs: that they have never formed by liquid-phase differentiation, but rather by
carbonyl decomposition reaction and CVD growth of large monocrystals of FeNi
austenite. This process could explain some properties that do not fit into the
liquid-phase differentiation model (e.g. primordial noble gas contents). He also
argues, that smelting and solidification processes can - even at low cooling rates -
hardly explain the large size of observed FeNi single crystal grains, structure and
composition of silicate and intermetallic phases as well as the absence of dendritic
structures in the known iron meteorites. To my opinion, Gero Kurat's model can become
an sound theory of planetesimal formation in the solar system which expains the large
number of ungrouped and chemically exotic iron meteorites.
J�rn / MetBase
Reference:
Gero Kurat (2003) Why iron meteorites cannot be samples of planetesimal smelting. In:
Papers presented to the INTERNATIONAL SYMPOSIUM Evolution of Solar System Materials: A
New Perspective from Antarctic Meteorites, held at the National Institute of Polar
Research, Tokyo, September 3 - 5, 2003. (Abstract #35)
Unfortunately, there is no online link to the abstract, but I can send a scanned image
of this abstract to those who are interested.
See also: http://presolar.wustl.edu/ref/LPSC2003_SanJuan.pdf
> -----Urspr�ngliche Nachricht-----
> Von: almitt [mailto:[EMAIL PROTECTED]
> Gesendet: Mittwoch, 20. Oktober 2004 03:36
> An: Bernhard Rems
> Cc: [EMAIL PROTECTED]
> Betreff: Re: [meteorite-list] There are no silly questions? Wait until
> you haveread that :-)
>
>
> Hi Bernhard and all,
>
> Bernhard Rems wrote:
>
>
> 4) Iron meteorites originate from the core of a large and destroyed
> 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?
>
> AL says:-)
>
> O.K. one other comment from me then I'll give people a brake.
> Most of the
> Iron meteorites come from 12 distinct parent bodies (based on chemical
> classification). We then have an additional 80 some anomalous
> that provide us
> with the remainder of our iron meteorites. Some 86% of all
> iron meteorites
> belong to the 12 main groups.
>
> As McSween says the core of the problem, is iron meteorites
> have pretty plain
> spectra and light coming from them (albedo) is poor. Also
> iron meteorites
> represent a highly differentiated body one that has been
> heated (of course)
> and altered doing a resetting of the isotopes that might help
> us shed light
> on their origin. Silicates we find in iron meteorites
> sometimes help us out a
> bit with this.
>
> --AL Mitterling
>
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