AW: [meteorite-list] There are no silly questions? Wait untilyouhaveread that :-)
From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Wed Oct 20 14:38:55 2004
J?rn provocatively wrote:
>where is all the crust gone? Why don't we have many more
>at least 92) different types of achondrites in our
>meteorite collections? If it was possible to break
>up the parent bodies down to the metal core, and to
>deliver samples of these cores down to earth as
Thank you for forcing us to think about this puzzling question. It was one question I can identify with, but carelessly swept under the rug somewhere along the line and forgot.
Please send me your abstract for the Kurat paper, and kindly comment on this alternate view I might suggest as an enthusiastic amateur:
1. Iron meteorites we all know are disproportionately represented vs. achondrites because both recognize and also find so many of them after achondrites have long crumbled...so there is a much larger diversity represented is part of your answer.
2. Achondrites especially such as Winonites, possible Ureilites and even brachinites, Acapulcoites-Lodranites share ages similar to most of the 92 odd- "distinct" irons you are mention. These achondrites all seem to have an age similar to irons, 4.5 billion years old.
3. While we are in a pleasant thinking-out-loud discussion on alternate theories to iron meteorite genesis, how about considering the planet Mercury. The hot world it is, the temperature would seem to be a driver of this. Do you know what is the crust to iron core fraction of Mercury? It is tiny. No doubt in the Solar System's Beginning, there were a few huge body smashes. Now a little more "food for thought". It seems very plausible to me that a protoplanet of a Mercury like composition I call "Merky" for convenience, smashed into bits (this is much more likely than not, as the solar system's current "9" planets certainly has not been the story since day 1), and continued sweeping (aggregating) for some changes in composition. The main results of such a collision, might very well be a Merkyoid Family, principally iron, if one considers the composition as such, which is not unlikely in my opinion. Perhaps all the terrestrial planets have higher iron ratios than the accepted iron content of the primo
rdial matter - I didn't check) Then, it becomes an easy exercise to produce all the irons "types" one wants, just by varying the distance (orbital radius) they are to the Sun and exactly what time frame they happened, to get the deramping of temperature to produce all the forms we are discussing...Oh and at this early stage of the Solar System, it is quite clear to me that plenty of meteoroids would aggregate at high temperatures to some of these larger chips to help create differences in composition, not to mention that in a large proto-parent high iron core % body like Merky, doesn't have to be uniform like well mixed water in a glass ... more onion skinny with plenty of local variation to keep researcher busy for a long time.
Do we need pressures to get the Widmanstatten patterns or just initial smelting and later temperature as this model provides in profusion...Now, perhaps we will learn more from Messenger, and it would be wonderful to get some closeups of a few representative all-iron asteroids in situ to study their surface geology...
Sure there are plenty of whole to polk in the above scenario, but I feel the general ideas presented in this light may have some merit? What do you think?
Just a little correction: of course, there are iron meteorites which come from differentiated parent bodies (so called magmatic group). IIIAB is such a group.
If all ungrouped iron meteorites are derived from the cores of differentiated bodies, the question is:
J?rn / MetBase
> -----Urspr?ngliche Nachricht-----
> Von: J?rn Koblitz
> Gesendet: Mittwoch, 20. Oktober 2004 17:44
> An: almitt; Bernhard Rems
> Cc: Meteorite-list_at_meteoritecentral.com
> Betreff: AW: [meteorite-list] There are no silly questions? Wait until
> youhaveread that :-)
> 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
> 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:almitt_at_kconline.com]
> > Gesendet: Mittwoch, 20. Oktober 2004 03:36
> > An: Bernhard Rems
> > Cc: Meteorite-list_at_meteoritecentral.com
> > 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
Received on Wed 20 Oct 2004 02:38:32 PM PDT