[meteorite-list] Re: Mercury Meteorite Puzzle

From: Treiman, Allan <Treiman_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:49 2004
Message-ID: <9CBE44BF7DE9D511960300500424D7D0112248_at_cassnt2>

Hi, all --=20

  Here's my two cents on NWA 011.=20
  I think Mercury is unlikely. Reflection spectra of=20
Mercury seem to say that its crust is nearly free of=20
iron in its minerals, except perhaps as iron metal.=20
That would rule out NWA 011. Some folks have
suggested that aubrites might be from Mercury, as=20
their minerals are nearly iron-free.=20
   Venus seems unlikely too. Its surface is so hot, and
its atmosphere so rich in sulfur dioxide, that all its=20
surface rocks ought to be altered form sulfates. Especially
plagioclase feldspar ought to be altered to form anhydrite
(CaSO4).=20
   So I vote for an asteroid.

  Allan

> -----Original Message-----
> From: Norbert Classen [SMTP:trifid_at_timewarp.de]
> Sent: Thursday, May 16, 2002 5:28 PM
> To: Robert Verish
> Cc: meteorite-list
> Subject: AW: [meteorite-list] Re: Mercury Meteorite Puzzle
>=20
> Hello Rob, hello Mercury enthusiasts,
>=20
> 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...
>=20
> 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.
>=20
> 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.
>=20
> 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...
>=20
> Best regards,
> Norbert Classen
>=20
> --------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 =B1 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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>=20
>=20
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Received on Fri 17 May 2002 03:17:58 PM PDT