[meteorite-list] Moss Meteorite From A Comet?

From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Sun Aug 20 04:23:08 2006
Message-ID: <009301c6c42f$763c5410$81598b90_at_mandin4f89ypwu>

Howdy Bernd, Rick & all,

Just curious because I recently read somewhere (maybe this list actually but
can't remember) that the CH (or CB?) chondrites may now be the best match to
a cometary origin. I think this was after Deep Impact. Anyone remember or
know more?

Cheers,

Jeff

----- Original Message -----
From: bernd.pauli_at_paulinet.de
To: Meteorite-list_at_meteoritecentral.com
Sent: Sunday, August 20, 2006 6:46 AM
Subject: [meteorite-list] Moss Meteorite From A Comet?


Hello Rick and List,

As you are new on this List, I don't really know who I am talking to, how
old or how young you are, how much you know about meteorites and comets,
if you already have any meteorites, whether you have already read any books
about meteorites, etc., etc. Maybe you would like to introduce yourself to
us and tell us a little bit about you. Thank you in advance!

Your question is interesting and intriguing. Theoretically, some meteorites
may have a cometary origin but so far they have not been found or recognized
yet.
If there are cometary meteorites in our collections, scientists expect them
to
have come from the so-called Kuiper belt beyond 30 AU.

Their silicates should be anhydrous, highly unequilibrated, their chemistry
would
resemble that of chondrites but there would be a high amount of C and N. But
if
these cometary meteorites were altered through the influence of flowing
water so
far out in our Solar System, the most likely candidates here on Earth would
be
the CI carbonaceous chondrites.

Some xenolithic inclusions in ordinary chondrite regolith breccias are also
suspects for a cometary origin.

You will probably have seen a Perseid fireball but no matter what you saw,
some scientists say that many shower meteors can be as dense as carbonaceous
chondrites or even as dense as ordinary chondrites.

Especially interesting is the fall of the CI chondrite Revelstoke because it
could be an example of a weak cometary meteorite. A fireball was observed
for
hundreds of kilometers and atmospheric effects were measured nearly 1500 km
away. The fireball must have been as energetic as the Sikhote-Alin
meteorite.
The SA fireball produced several craters and tons of meteoritic irons but
all
that was found of the Revelstoke fireball was less than a gram of friable
black
rock.

If there are cometary meteorites in our collections,
here are some of the criteria they should meet:

a) as rare as CI carbonaceous chondrites
b) dark + weak
c) highly porous + low density (ca. 2 g/cm3)
d) nearly solar abundances
e) high abundance of C, N, and organic compounds
f) anhydrous silicates
g) highly unequilibrated silicates
h) very large abundance of interstellar grains
i) chondrules and CAIs should be rare or absent

It is so difficult to identify cometary meteorites in case they already
exist
in our collections because they could easily be misclassified as
achondrites.
There are indeed achondrites like the acapulcoites, lodranites, brachinites,
winonaites that have chondritic chemical abundances, and there are C-rich
achondrites, for example the ureilites.

And now back to your question: Is the Moss meteorite from a comet?

Let's *suppose* some cometary meteorites do contain chondrules, then C-rich,
highly unequilibrated CO, CV, or ordinary chondrites might be good
candidates
according to:

CAMPINS H. and SWINDLE T. (1998) Expected characteristics
of cometary meteorites (MAPS 33-6, 1998, pp. 1201-1211).

In other words, in that case even the Moss meteorite - if it should really
be classified as a CO.x (preferentially "x" should be 1, 2, or 3) - could
be of cometary parentage.

Hope this helps ;-)


Best regards,

Bernd

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Received on Sun 20 Aug 2006 04:05:51 AM PDT