[meteorite-list] [2] Asteroid Or Comet Sutters Mill

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Thu, 3 May 2012 00:04:45 -0400 (EDT)
Message-ID: <8CEF6F902A1CC7A-C0C-78876_at_webmail-d007.sysops.aol.com>

Or NEO (175706) 1996 FG3 !

(MPOD 24 Oct 2011)

Kindest wishes
Doug

-----Original Message-----
From: lebofsky <lebofsky at lpl.arizona.edu>
To: aerubin <aerubin at ucla.edu>
Cc: meteorite-list <meteorite-list at meteoritecentral.com>
Sent: Wed, May 2, 2012 11:47 pm
Subject: Re: [meteorite-list] Asteroid Or Comet Sutters Mill


Hi Again:

One other place that seems to have abundant CM-like material, the
surface
of Vesta. There are dark areas on Vesta that seem to be composed of
carbonaceous chondritic material (based again on albedo and spectrum). I
do not know all of the details (missed some of the papers at the Lunar
and
Planetary Science Conference), but my impression is that the dark
material
did have the spectral signature of material altered by water, implying
that Vesta has been hit over time by C-class asteroids. This is
consistent
with what Alan is saying about clasts in howardites (which a thought to
come from Vesta).

To answer your question, Mike, once you alter (hydrate) the silicate
material and make a phyllosilicate, it is not that easy to get rid of
the
water (need temperatures that are in the hundreds of degrees centigrade.
You just needed temperatures low enough when the asteroids formed for
water to condense out, probably the middle of the present asteroid belt.

Larry


> CM chondrites are also ubiquitous. The most abundant foreign
> component of the lunar soil is chemically similar to CM chondrites.
> If i recall, many fireballs also seem to be CM like, although other
> list members would be better able to address this point. More CM
> chondrites would be in our meteorite collections if they weren't so
> friable. There are also many CM clasts in meteorite breccias, both
> ordinary chondrite regolith breccias like Abbott, Plainview, Dimmitt
> and Fayetteville, and howardites such as Kapoeta. This ubiquity
> mandates a reliable local source, i.e., not a comet but an asteroid.
> Some of the clasts in ordinary chondrites are unshocked, meaning that
> they came in at low relative velocities, also very un-comet like. As
> the asteroid guys say, the CM chondrites are probably from some types
> of C asteroids located at the outer reaches of the main belt; at those
> places ambient temperatures are low and volatiles are more likely to
> remain on the parent body. That is why CMs contain about 9 wt.% water
> (within phyllosilicates) and CI chondrites contain appreciably more.
>
>
> Quoting Michael Gilmer <meteoritemike at gmail.com>:
>
>> Hi List,
>>
>> This is great stuff. Thanks to Alan and Larry for enlightening us on
>> this.
>>
>> There has been some talk of the volatiles content of CM meteorites.
>> So, is it safe to assume that CM meteorites also originate from the
>> darker outer reaches of the asteroid belt where Tagish Lake hails
>> from? Meteorites rich in volatiles presumably come from that region
>> where solar effects are minimized?
>>
>> Best regards,
>>
>> MikeG
>>
>> --
>> -----------------------------------------------------------
>> Galactic Stone & Ironworks - MikeG
>>
>> Web: http://www.galactic-stone.com
>> Facebook: http://www.facebook.com/galacticstone
>> Twitter: http://twitter.com/GalacticStone
>> RSS: http://www.galactic-stone.com/rss/126516
>> -----------------------------------------------------------
>>
>>
>>
>> On 5/2/12, lebofsky at lpl.arizona.edu <lebofsky at lpl.arizona.edu> wrote:
>>> Hi Alan:
>>>
>>> I would agree with you on the consensus that CMs would appear to
come
>>> from
>>> asteroids. Based on spectra and albedo, CM meteorites look like
C-class
>>> (and possibly several other low-albedo classes) asteroids (very
common
>>> in
>>> the Main Belt). These are asteroid that have surface compositions
>>> showing
>>> that they have been exposed to liquid water, phyllosilicates.
>>>
>>> There is no (or little) evidence that comets have had interiors warm
>>> enough to melt ice and create the water necessary to form
>>> phyllosilicates.
>>>
>>> Larry
>>>
>>>> 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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>>>>
>>>> ______________________________________________
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>>>
>>> ______________________________________________
>>>
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>>
>
>
>


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Received on Thu 03 May 2012 12:04:45 AM PDT