[meteorite-list] Wanted: Meteorites from Mercury

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 8 Jan 2012 15:44:26 -0600
Message-ID: <8C3C0F61ACE547BAA3F7E2510550BA80_at_ATARIENGINE2>

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
---------------------------------------------------------------
----- Original Message -----
From: "Galactic Stone & Ironworks" <meteoritemike at gmail.com>
To: "Stuart McDaniel" <actionshooting at carolina.rr.com>
Cc: <baalke at zagami.jpl.nasa.gov>; "meteoritelist meteoritelist"
<meteorite-list at meteoritecentral.com>
Sent: Sunday, January 08, 2012 2:54 PM
Subject: Re: [meteorite-list] Wanted: Meteorites from Mercury


> Hi Pete and List,
>
> There is really no evidence that supports the Mercury-angrite
> connection. However, if a meteorite from Mercury is ever confirmed,
> it is expected to be similar to angrites. Because angrites are so
> unusual (in comparison to other meteorites) and they possess
> properties that would be expected from a Mercury meteorite, they are
> the leading candidates. But as far as I know, nothing definitive has
> ever come to light that makes a solid connection between angrites and
> Mercury (or any other parent body).
>
> Best regards,
>
> MikeG
>
> --
> *************************************************
>
> Galactic Stone & Ironworks - Meteorites & Amber (Michael Gilmer)
>
> Website - http://www.galactic-stone.com
> Facebook - http://tinyurl.com/42h79my
> News Feed - http://www.galactic-stone.com/rss/126516
> Twitter - http://twitter.com/galacticstone
>
> ***************************************************
>
> On 1/8/12, Stuart McDaniel <actionshooting at carolina.rr.com> wrote:
>> That is what was mentioned in the article.
>>
>>
>>
>> Stuart McDaniel
>> Lawndale, NC
>> Secr.,
>> Cleve. Co. Astronomical Society
>> IMCA #9052
>>
>> http://spacerocks.weebly.com
>> -----Original Message-----
>> From: Pete Pete
>> Sent: Sunday, January 08, 2012 3:12 PM
>> To: baalke at zagami.jpl.nasa.gov ; meteoritelist meteoritelist
>> Subject: Re: [meteorite-list] Wanted: Meteorites from Mercury
>>
>>
>>
>>
>> Hi, All,
>>
>>
>>
>> I know there's been only scattered remarks about the Messenger
>> mission, but
>> is the current consensus that angrites do not originate from Mercury?
>>
>>
>>
>> Best,
>> Pete
>>
>>
>>
>>> From: baalke at zagami.jpl.nasa.gov
>>> To: meteorite-list at meteoritecentral.com
>>> Date: Fri, 6 Jan 2012 10:20:11 -0800
>>> Subject: [meteorite-list] Wanted: Meteorites from Mercury
>>>
>>>
>>> http://www.skyandtelescope.com/news/Wanted-Meteorites-from-Mercury-136803313.html
>>>
>>> Wanted: Meteorites from Mercury
>>> By Kelly Beatty
>>> Sky & Telescope
>>> January 6, 2012
>>>
>>> During a recent science conference discussing Messenger's results
>>> from
>>> Mercury, investigator Shoshana Weider (Carnegie Institution of
>>> Washington) commented, "Short of landing on the surface, picking up
>>> a
>>> rock, and bringing it home, the instruments on Messenger that
>>> characterize chemistry are the best we're going to get."
>>>
>>> Well, Shoshana, you might still get to hold such a rock someday.
>>>
>>> According to a 2008 analysis
>>> <http://arxiv.org/ftp/arxiv/papers/0801/0801.4038.pdf> by Brett
>>> Gladman
>>> and Jaime Coffey (University of British Columbia), chunks of Mercury
>>> should be lying somewhere on Earth right now. The dynamicists
>>> conclude
>>> that 2% to 5% of the debris blasted by impacts off the surface of
>>> Mercury at or above escape velocity (2.6 miles per second) should
>>> reach
>>> Earth within 30 million years.
>>>
>>> Their numbers suggest that Mercurian meteorites should be roughly
>>> one
>>> third as common as those from Mars, for which the count now stands
>>> at 60.
>>> Gladman conservatively suggests that at least a half dozen stones
>>> should
>>> be
>>> lying around somewhere on terra firma.
>>>
>>> Meteorite collectors would value a Mercurian meteorite above all
>>> others,
>>> likely fetching $5,000 or more per gram, so they've been on the
>>> lookout
>>> for one. A few years ago, prior to Messenger's arrival,
>>> meteoriticists
>>> had speculated that the best existing match to Mercury were a rare
>>> handful of ancient, basalt-rich stones known as angrites
>>> <http://research.jsc.nasa.gov/PDF/Ares-1.pdf>.
>>>
>>> But even before Messenger's arrival, ground-based astronomers had
>>> concluded that Mercurian surface rocks contained very little iron -
>>> strange indeed, given that the innermost planet has an iron core
>>> that
>>> takes up 80% of its diameter and more than half of its volume!
>>>
>>> "At that time," comments geochemist David Blewett (Applied Physics
>>> Laboratory), "people were expecting Mercury to have a composition
>>> more
>>> like a lower-iron version of the lunar highlands. We now know that
>>> it's
>>> much different than that." After nearly a yearly scrutinizing the
>>> planet
>>> from orbit, Messenger has confirmed that iron is in short supply at
>>> the
>>> surface.
>>>
>>> Instead, the compositional clues suggest that a Mercurian meteorite
>>> would
>>> be an igneous rock - or perhaps a fused breccia of different rock
>>> types -
>>> rich in magnesium and volatile elements (especially sulfur and
>>> potassium).
>>> This closely matches the composition of another rare meteorite
>>> group,
>>> the aubrites. Also known as enstatite achondrites, aubrites are
>>> igneous
>>> rocks dominated by the iron-free mineral enstatite (Mg_2 Si_2 O_6 ).
>>>
>>> But aubrites aren't from the innermost planet. For one thing,
>>> they're
>>> too reflective - anything coming from Mercury would be much darker,
>>> tinted by some yet-to-be-identified compound that's seen widely
>>> <http://photojournal.jpl.nasa.gov/catalog/PIA14492> in Messenger's
>>> images. It might also smell faintly of sulfur, appear heavily
>>> shocked,
>>> exhibit significant exposure to cosmic rays, and might even be
>>> slightly
>>> magnetic. Such characteristics would certainly have come to the
>>> attention of hunters and collectors, and it's safe to say that none
>>> of
>>> the world's 40,000 well-documented meteorites are from Mercury.
>>>
>>> Yet dynamical probabilities argue otherwise, so why haven't such
>>> samples
>>> been found? Gladman and Coffey didn't address how chunks of rock
>>> might
>>> get blasted off the Mercurian surface, only that the high collision
>>> velocities of asteroids and comets should make it easy to do so.
>>>
>>> Maybe the launch mechanics aren't understood well enough, suggests
>>> Jay
>>> Melosh, an impact specialist at Purdue University. "Perhaps at the
>>> very
>>> high speeds required for direct transfer, the fragments are simply
>>> too
>>> small," he says. "These ejecta have to be launched from the surface
>>> very close to the impact point - and perhaps our current models do
>>> not
>>> give very good results here." However, Messenger finds that big
>>> impacts
>>> on Mercury are accompanied by clusters of secondary pits, created by
>>> tossed-out debris, that are generally much larger - not smaller -
>>> than
>>> those around comparable lunar craters. "This fact is one of the
>>> current
>>> big puzzles about the Mercurian cratering record," Melosh concedes.
>>>
>>> And so the search goes on for what will almost certainly be the most
>>> celebrated meteorite discovery since the finding of stones blasted
>>> from
>>> surfaces of the Moon and Mars a few decades ago.
>>>
>>> ______________________________________________
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Received on Sun 08 Jan 2012 04:44:26 PM PST