[meteorite-list] Wanted: Meteorites from Mercury

From: Carl Agee <agee_at_meteoritecentral.com>
Date: Mon, 9 Jan 2012 06:55:03 -0700
Message-ID: <CADYrzhoL1x3sJ6Q61cq7LyC0OVdtGxSyKNWtOEf33TOZ8u+EQA_at_mail.gmail.com>

Sterling makes some good points. The other thing besides trapped
atmospheric gases that make the SNC's "planetary" is their relatively
young igneous crystallization ages (except for ALH84001) -- indicating
geologically long-lived volcanism on a large parent body. All angrites
have ancient crystallization ages, in fact SAH99555 has perhaps the
oldest crystallization age of any igneous rock in the known solar
system. It is assumed that a body of Mercurian size would have at
least a billion years of igneous activity and probably longer (like
the Moon). If so it might take several 10's of millions of years to
form a permanent crust from which to derive meteorites. Hence the
"zero age" of angrites do not fit this picture well, more likely a
smaller body, but not definitive. On the other hand, neither do the
aubrites. As much as I would like our "low-FeO" 1-ton Norton County
aubrite to be a Mercurian meteorite, this also seems unlikely because
of it ancient age ~4.55 BY. The color argument is a tricky one because
we have no idea what causes the Mercurian regolith to be darker than
say an aubrite, and this is because of the intense stream of solar
wind on rock surfaces which may have a huge on surface coloration.
Another thing to remember is that none of the orbiters at Mars have
ever spotted a terrain on the martian that is exactly the same as SNC
meteorites, so based just on orbital data you would never know SNCs
are from Mars -- dust coating is a big problem. There probably isn't
as much dust on Mercury, but keep in mind that the interpretation of
spectral data from orbit is as much art as it is science and
ground-truth calibrations are hard to come by, so knowing the Sun's
interaction with the Mercurian regolith maybe just as problematic.
This is definitely a work in progress! Of course a NASA sample return
mission would be my recommendation! I'm not picky, Mercury, Venus,
Mars...

Carl Agee


---------------------------------------------------
Message: 7
Date: Sun, 8 Jan 2012 15:44:26 -0600
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
Subject: Re: [meteorite-list] Wanted: Meteorites from Mercury
To: "Galactic Stone & Ironworks" <meteoritemike at gmail.com>, "Stuart
       McDaniel" <actionshooting at carolina.rr.com>
Cc: baalke at zagami.jpl.nasa.gov, meteoritelist meteoritelist
       <meteorite-list at meteoritecentral.com>
Message-ID: <8C3C0F61ACE547BAA3F7E2510550BA80 at ATARIENGINE2>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
       reply-type=original

Hi,

You may or may not remember that what made
possible the positive identification of Martian
meteorites AS Martian meteorites was that we
had samples from the Martian surface.

No, not rock samples, nor any returned samples,
but the isotopic composition of rare gases in the
Martian atmosphere, which made a distinctive
and unusual signature (particularly for Argon).

The SNC's shared this unique signature. It was
like a fingerprint. And possible only because we
had a lander on the surface.. Mercury has no
atmosphere of any consequence and we have
no lander there.

It's always possible that our present sensing
capacity will turn up something as definite, but
I can't think of what it could be. Believe me, I've
tried.


Sterling K. Webb

-- 
Carl B. Agee
Director and Curator, Institute of Meteoritics
Professor, Earth and Planetary Sciences
MSC03 2050
University of New Mexico
Albuquerque NM 87131-1126
Tel: (505) 750-7172
Fax: (505) 277-3577
Email: agee at unm.edu
http://meteorite.unm.edu/people/carl_agee/

Received on Mon 09 Jan 2012 08:55:03 AM PST