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

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Thu, 3 May 2012 10:02:34 -0700
Message-ID: <b04d1ea41d2159fedac45784426aff8d.squirrel_at_webmail.lpl.arizona.edu>

Not guilty!

It was 1.2 AU away from the Earth at the time--nice try! There are,
however other C-type NEOs that are around and could keep our supply up.

By the way, 13 of the 20 largest asteroids in the Main Belt are either
C-type or B-type and I think that all of them have the spectral signature
of hydrated silicates and make up something like 45% of the mass of the
entire asteroid belt (Ceres itself is 1/3 of the entire mass of the
asteroid belt). So lots of potential sources for CM meteorites, though I
think that 10 Hygiea is the best candidate at the moment (spectrum,
location, etc.).

Larry

> 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 01:02:34 PM PDT