[meteorite-list] Asteroid Or Comet Sutters Mill

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Wed, 2 May 2012 14:50:53 -0700
Message-ID: <0001336CEC624DB7AE49FE11A1CF9BEC_at_igpp.ucla.edu>

I guess I've been goaded into responding.
First, at this point we don't know if the meteorite is a CM chondrite or
not. No meteorite researcher has completed an analysis of it yet (perhaps
tomorrow or Friday) and I have not seen a piece.
But, on the more general question of CM chondrites, most researchers believe
that the carbonaceous chondrites all are derived from asteroids. There is
more or less a continuum in properties across the chondrite groups; it is
difficult to imagine that they are from different classes of parent bodies,
i.e., asteroids vs. comets. All chondrite groups (except CI) contain
chondrules, CAIs, matrix, metal and sulfide although the abundances of these
phases can vary a lot among the groups. Even CI chondrites contain a few
olivine and pyroxene grains that seem to be chondrule fragments, a few
refractory mineral grains that seem to be CAI fragments, and even one
reported intact CAI. Furthermore, the isolated olivine and pyroxene grains
in CI chondrites have the same olivine Fa vs. CaO distribution as in CM
chondrites suggesting that they are from a similar source.
I think that the CM chondrites are from an asteroid that was fairly porous
and had a fair amount of water, present either as ice or in phyllosilicates.
Stochastic impacts on this asteroid caused fracturing in some regions more
than others and during subsequent aqueous alteration (probably caused by
impact mobilization of water), the more fractured regions retained more
water and became more altered.


Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA 90095-1567
phone: 310-825-3202
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html


----- Original Message -----
From: "Matson, Robert D." <ROBERT.D.MATSON at saic.com>
To: "meteorite-list" <meteorite-list at meteoritecentral.com>
Sent: Wednesday, May 02, 2012 2:16 PM
Subject: Re: [meteorite-list] Asteroid Or Comet Sutters Mill


> Hi Paul,
>
> Probably not a misquote -- Dr. Jenniskens is interested in deciphering
> the
> nature of the original asteroid (meteoroid) body that produced the
> meteorites. The original body was large enough that it may not have been
> a monolithic body; as with 2008 TC3 (Almahata Sitta), the pre-encounter
> body may have been a rubble pile, consisting of more than just CM2
> material. In any case, I don't think the parent body (or bodies) for CM2
> is cometary. Would be interested in hearing Dr. Rubin's theory on the
> nature of the CM2 parent. --Rob
>
> -----Original Message-----
> From: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Paul
> Gessler
> Sent: Wednesday, May 02, 2012 2:08 PM
> To: meteorite-list
> Subject: [meteorite-list] Asteroid Or Comet Sutters Mill
>
> In the LA times article it reads in part:
>
> We want to learn about this asteroid," said Peter Jenniskens, an
> astronomer and senior research scientist at the Carl Sagan Center at the
> SETI (Search for Extraterrestrial Intelligence) Institute and the NASA
> Lunar Science Institute. "This is scientific gold."
>
> I hope/probably they miss quoted him?
>
> I vote comet
>
> Paul G
>
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Received on Wed 02 May 2012 05:50:53 PM PDT