[meteorite-list] Re: Mercury Meteorite Puzzle

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:49 2004
Message-ID: <3CE6A3F5.DB375123_at_bhil.com>

Hi, Eric, List,

    The generally accepted explanation for the olivine crystals is that only at
the base of the mantle (at the mantle/core boundary) do you find the temperature,
pressure, and most important: the slow cooling times, that make the formation of
pure olivine crystals possible.
    As to their survival on the Earth's surface, pure olivine does not survive
long in the presence of water. Which brings us to another mystery: the detection
of wide distributions of olivine on Mars, which sets a limit for "wetness" far
lower than what we (would like to) think is the extent of Martian water.
Mysteries everywhere. It's what makes being alive in the universe fun...

Sterling
--------------------------------------------------------------------------
Starbits_at_aol.com wrote:

> Ron Baalke wrote:
>
> <Since Mercury and Venus are inside of Earth's orbit, then by the process of
> elimination, that would indicate the parent body for E chondrites are either
> Mercury or Venus. OK, fair enough.>
>
> and
>
> <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".
>
> If people are interested in a mystery here is a big one. Pallasites are
> generally
> assumed to be from the core / mantle boundry. There are quite a few
> pallasites
> so their formation doesn't appear to be an unusual occurance. There are
> also a
> lot of irons from the core side of the boundry. There are however no, as in
> zero, meteorites with pallasitic type olivine crystals with out an iron
> matrix.
> 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?
> Is there
> a yet undiscovered class of meteorites? Is there a mechanism that prevents
> the formation of a pure olivine region or destroys them after formation,
> preventing
> a pure olivine meteorite from reaching earth? There are no answers. The
> big mystery isn't whether we have a meteorite from mecury, it is where is the
> olivine?
>
> Eric Olson
> http://www.star-bits.com
>
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Received on Sat 18 May 2002 02:56:54 PM PDT