AW: [meteorite-list] Re: Mercury Meteorite Puzzle

From: Norbert Classen <trifid_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:49 2004
Message-ID: <NCBBKMGDKLMGIBALJOFCAEMACLAA.trifid_at_timewarp.de>

Hello Rob, hello Mercury enthusiasts,

It's not okay! I think the statement that "NWA 011 has an
oxygen isotope ratio that indicates it came from a body
larger than a big asteroid" is quite nonsensical. What's the
connection between oxygen isotope ratios and the size of
a planet or an asteroid? If that would be true the aubrites
would qualify as planetary meteorites, too, since they
share the Earth's O-isotopic ratio...

Okay, I'm no planetary scientist, but what I've learned
from my private studies on planetary meteorites is that the
person who wrote this article mixed up some things. The facts
suggesting NWA 011's origin from a larger body are most
probably the unusually high FeO/MnO ratios similar to lunar
values, although they are slightly lower for pyroxenes in
NWA 011.

However, do the other data on NWA 011 suggest a planetary
or Mercurian origin of this peculiar achondrite? I don't
think so. Look at the data, NWA 011 has been described as
"virtually unshocked", a fact making it hard to believe that
this rock has been blasted off a planet. None of its
plagioclase has been converted to maskelynite - the rims of
the plagioclase crystals in NWA 011 aren't even slightly
distorted. From what we know about lunar and Martian
meteorites it seems quite improbable that this strange
rock is of planetary origin at all. Don't get me wrong,
I would be glad if we finally had the first Mercurian rock,
and I would be willing to pay dearly for even a small piece.

Please correct me if I'm wrong. As stated above, I'm no
planetary scientist, but from what I know I must conclude
that the "Mercurian origin" of NWA 011 is nothing but a
wild guess. Has anyone seen data on the REE distribution
in NWA 011 so far? Why don't they show as a nice "S"??
Now, that would be something...

Best regards,
Norbert Classen

--------Rob Verish wrote-------
>
> "NWA 011 has an oxygen isotope ratio that indicates it
> came from a body larger than a big asteroid."
>
> Okay. This article explains to me why this meteorite
> came from a body larger than an asteroid. But it
> doesn't explain how the other "planet-sized bodies" in
> our solar system are being ruled-out in favor of
> Mercury.
>
> Is there an upper limit for the suspect "planet-sized"
> parent body, that would exclude Mars, Venus, or Earth!
> (The 81Kr-Kr age for NWA011 is 39 ± 5 Ma, which can be
> interpreted as an upper limit of the cosmic-ray
> exposure age, which would exclude the proto-versions
> of these inner planets)?
>
> Same-sized planetary bodies? We know enough about the
> Moon to rule out a Lunar-origin, but do we know enough
> about the Galilean moons of Jupiter to rule them out?
>
> It would be interesting to see a matrix showing
> suspect parent bodies vs. NWA 011 data, and to see
> which evidence favors which "planet-sized body".
>
> Here's what we already know:
>
> April12th issue of Science, Akira Yamaguchi (National
> Institute of Polar Research, Tokyo)
> <http://www.sciencemag.org/cgi/content/short/296/5566/334>
>
> Meteoritical Bulletin 84, Table 9
>
> ----------------------------------
> [meteorite-list] MAPS and Mercury
>
> Bernd Pauli HD bernd.pauli_at_lehrer1.rz.uni-karlsruhe.de
>
> Sun, 14 Apr 2002 15:20:10 +0200
>
> Marco wrote:
>
> > By the way, I remember that some time ago a paper on
> the characteritsics and expected numbers of meteorites
> from several parent bodies (including Mercury and
> Venus) has been published in Meteoritics & Planetary
> Science.
> > Sorry I do not have an exact reference ready at the
> moment: that's because I am packing up to move to
> another house currently. But a search on NASA ADS will
> probably reveil it to you.
>
>
> LOVE S.G. et al. (1995) Recognizing mercurian
> meteorites (MAPS 30-3, 1995, 269-278).
>
> ROBINSON M.S. et al. (2001) Ferrous oxide in Mercury's
> crust and mantle (MAPS 36-6, 2001, pp. 841-847).
>
> Best regs,
>
> Bernd
> -------------------------------------------
>
> [meteorite-list] Mercury Meteorite Puzzle
>
> Ron Baalke baalke_at_zagami.jpl.nasa.gov
> Thu, 16 May 2002 10:38:56 -0700 (PDT)
>
> http://news.bbc.co.uk/hi/english/sci/tech/newsid_1991000/1991394.stm
>
> Mercury meteorite puzzle
>
> Is this from Mercury, the planet closest to the Sun?
>
> By Dr David Whitehouse
> BBC News
> May 16, 2002
>
> The first meteorite that may have come from Mercury
> has been identified.
>
> NWA 011 was found in the Moroccan Sahara in December
> 1999 and was immediately regarded as something
> unusual.
>
> It clearly had a molten past and was formed from
> lighter materials than most meteorites. This implied
> it had once been part of a much larger body.
>
> It was originally classified as a eucrite, a group of
> meteorites thought to be from the asteroid Vesta. But
> a detailed analysis of NWA 011 showed it to be
> different.
>
> Now, researchers speculate that it is the first known
> meteorite from our Solar System's innermost planet,
> Mercury.
>
> Rocks blasted off Mercury by a large impactor would
> have a difficult journey to reach the Earth, say the
> researchers - but not impossible. Nevertheless, the
> calculations show such rocks would be an extremely
> rare find on Earth.
>
> NWA 011 has an oxygen isotope ratio that indicates it
> came from a body larger than a big asteroid. Japanese
> researchers say the basalt in NWA 011 suggests the
> body from which it did originate had a core of molten
> iron with an outer covering of silicon and aluminium
> that formed a basaltic crust.
>
> And that means a planet-sized body. Could it really be
> Mercury?
> ---------------------------------------------------
>
>
>
>
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Received on Thu 16 May 2002 08:27:30 PM PDT