[meteorite-list] Cometary meteorites

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Wed, 24 Nov 2010 19:02:10 -0800
Message-ID: <AANLkTin9t0paxYQrQPHWrcp60ax8X8ZnzR7wBBatN1sx_at_mail.gmail.com>

E.P., All,

We know quite a bit about comets' interiors based on the knowledge
that we have of where and how they formed, to say nothing of the
chemical and isotopic data that we've collected from analyses of
samples. These aren't finer details - you're stating that high
abundances of heavier elements for some reason existed in the Oort
Cloud/Kuiper Belt region.

You might as well state that CI-chondrites likely formed at the core
of externally CV-chondrite bodies.
To a layman, that might kind of make sense. CV-chondrites have more
metal in them and are generally more dense and depleted in volatiles
compared to CI-chondrites. But that's not how things worked in the
solar nebula. CV-chondrites formed a little closer to the sun, where
there was less volatile material available for incorporation (and more
heavier elements), and CI-chondrites generally formed farther from the
sun. And when those chondritic bodies formed, they were generally
homogeneous.

In order to get complex structures like the ones you're talking about
(core, "crust," etc.), you require differentiation.

There were no large chunks of rock out there upon which comets might
"nucleate." Comets formed at the same time as all of the other
smaller bodies in our solar system, and there were no large masses of
rock out there.

This is basic stuff.

http://adsabs.harvard.edu/full/1983A%26A...122..171Y

Comets *are* composed of some silicate material, because the volatiles
did nucleate about those silicate minerals. The trouble with your
theory is that silicates that far from the sun never accreted into
larger solid bodies, and the silicate cores I'm talking about (that
we've seen from comets) are measured in microns. That's the sort of
material that was accreting out there when comets were forming.
Theoretically you could try to say that bodies that formed in the
inner solar system could have been gravitationally flung out and into
the fringes of our solar system, where they could slowly accrete icy
shells of their own, but I'm pretty sure that you're not trying to
suggest such a process.

> If Tunguska can be associated with Comet Encke, then the spherules there might be some indication, but only of what's left of that particular comet.

We don't even know if the Tunguska impactor was related to a comet in
any way. It could have been asteroidal. To say that the Tunguska
body is associated with Comet Encke is akin to saying that Mazapil is
associated with the Andromedid meteor shower. The evidence is
circumstantial, at best.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6T-3T0T8W8-8&_user=10&_coverDate=03%2F31%2F1998&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1555037280&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5a790f2b98b8acb2cdb55072b77d74c1&searchtype=a

And if the body was cometary, it says nothing of whether or not comets
have solid, rocky cores, since no sizable fragments have been
recovered and all of the spherules and microscopic fragments yet found
point towards the entirety of the body being composed of (assumed)
volatiles and microscopic siliceous grains.

> If I remember correctly, Moss Lake is also associated with Comet Encke.

I can only assume that you're referring to Lake Cheko. Those claims
were made and fairly promptly refuted by a number of sources - this
gives you the basics.

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3121.2008.00791.x/full

> Aside from that, there is the "KT fossil" meteorite.

The fragment found by Frank T. Kyte has been determined likely to be a
fragment of a carbonaceous chondrite. Which says nothing about
whether or not it actually came from the K-T impactor, or if the
impactor was a comet. Meteorites fall all of the time - they were
falling when the K-T boundary layer was forming as well. It could
well be a piece of an unrelated meteorite.

But since most recent studies have determined that the K-T impactor
was likely a carbonaceous chondrite (not a comet), your argument here
is kind of unrelated.

http://www.sciencemag.org/content/282/5390/927.abstract

>There are several large circular holes in the surface of the Earth, surrounded by impactites, which have not been fully examined yet and which are likely to also contain comet samples.

You'll have to forgive me if I don't take your word for the existence
of craters or samples of comets that can't be verified by real
academics...

> In any case, we're likely soon to learn a whole lot more about Comet Schwassmann Wachmann 3, with very large (and very fast) samples possible in 2022.

I found quite a few articles referring to the comet and its break-up,
but nothing stating that there would be any possibility of fragments
coming much closer than seven to ten million miles from earth. There
have been talks of increased meteor shower activity due to it, but
that's because the solar wind has a much greater effect on smaller
particles over shorter periods of time.

I just don't understand where you're getting these ideas from. What
you're saying that doesn't outright disagree with accepted science is
at best conjecture.

Regards,
Jason

On Wed, Nov 24, 2010 at 4:25 PM, E.P. Grondine <epgrondine at yahoo.com> wrote:
> Hi Jason, all -
>
> What we know about the composition of the centers of comets is near zero.
>
> If Tunguska can be associated with Comet Encke, then the spherules there might be some indication, but only of what's left of that particular comet.
>
> If I remember correctly, Moss Lake is also associated with Comet Encke.
>
> Aside from that, there is the "KT fossil" meteorite. There are several large circular holes in the surface of the Earth, surrounded by impactites, which have not been fully examined yet and which are likely to also contain comet samples.
>
> In any case, we're likely soon to learn a whole lot more about Comet Schwassmann Wachmann 3, with very large (and very fast) samples possible in 2022.
>
> E.P. Grondine
> Man and Impact in the Americas
>
> --- On Tue, 11/23/10, Jason Utas <meteoritekid at gmail.com> wrote:
>
>> From: Jason Utas <meteoritekid at gmail.com>
>> Subject: Re: [meteorite-list] Cometary meteorites
>> To: "E.P. Grondine" <epgrondine at yahoo.com>, "Meteorite-list" <meteorite-list at meteoritecentral.com>
>> Date: Tuesday, November 23, 2010, 7:17 PM
>> Hello E.P. All,
>> We do not have examples of anything that even remotely
>> resembles what
>> actually constitutes cometary material.
>> What follows is an excerpt from an email that I posted to
>> the list on
>> August 11th of this year that addresses the same subject.
>> ---
>> The simple answer is no. ?No meteorites have ever been
>> found that
>> match all criteria for what we believe cometary material
>> should look
>> like.
>>
>> http://www.lpi.usra.edu/meetings/LPSC98/pdf/1004.pdf
>>
>> This is also the sort of topic that has been brought up
>> again and
>> again on the list. ?While I couldn't find any direct
>> references for
>> some reason, I was able to turn these up:
>>
>> http://www.mail-archive.com/meteorite-list at meteoritecentral.com/msg84604.html
>>
>> http://six.pairlist.net/pipermail/meteorite-list/2004-May/000683.html
>>
>> To condense: a few meteorites, namely the CI's, come close
>> to what we
>> think cometary material might look like. ?But those
>> meteorites weren't/aren't
>> associated with any known meteor showers, and are likely
>> just
>> fragments of ?D-class asteroids, which may or may not be
>> remnants of
>> "burned-out" comets (comets that got trapped in the
>> inner solar system
>> and stripped of most of their volatiles).
>> But, based on the above paper, even the CI's are probably
>> not actual
>> "cometary" material, though they fit the bill better than
>> most other
>> meteorites, for sure.
>> ...
>> Some more basic reading:
>> http://www.amsmeteors.org/faqm.html#11
>>
>> Scroll to section before bottom: "Meteorites
>> from Comets?"
>>
>> http://www.pibburns.com/catastro/meteors.htm
>> ---
>>
>> The assertion that CI meteorites are cometary in origin
>> goes against
>> practically every detail of cometary composition that we
>> have learned
>> over the past several decades, and the even more general
>> assertion
>> that cometary meteorites have been found and recognized is
>> thus simply
>> untrue.
>>
>> We may or may not have samples of the other asteroid
>> classes; that is
>> a completely different issue, and if you'd like to start a
>> new thread,
>> by all means do so.
>>
>> Regards,
>> Jason
>>
>> Jason Utas
>> University of California, Berkeley 2012
>> College of Letters and Science
>> Psychology, Geology
>>
>>
>> On Tue, Nov 23, 2010 at 4:46 PM, E.P. Grondine <epgrondine at yahoo.com>
>> wrote:
>> >
>> > Hi Larry -
>> >
>> > And when I started on this list there were no major
>> differentiated parent bodies for other meteorites (following
>> McSween), and now we have what, at least five?
>> >
>> > I suppose that if we knew what comets were, then there
>> wouldn't be any need to spend any money finding out what
>> they are. And then there is that tricky problem of the
>> source for C, B, G (and maybe D) asteroids.
>> >
>> > E.P.
>> >
>> > --- On Tue, 11/23/10, lebofsky at lpl.arizona.edu
>> <lebofsky at lpl.arizona.edu>
>> wrote:
>> >
>> > > From: lebofsky at lpl.arizona.edu
>> <lebofsky at lpl.arizona.edu>
>> > > Subject: Re: [meteorite-list] Cometary
>> meteorites
>> > > To: "E.P. Grondine" <epgrondine at yahoo.com>
>> > > Cc: warnerem at astro.umd.edu,
>> meteorite-list at meteoritecentral.com
>> > > Date: Tuesday, November 23, 2010, 3:48 PM
>> > > Hi:
>> > >
>> > > I have said this to you before that there is
>> about zero
>> > > evidence that
>> > > carbonaceous chondrites are from comets. There is
>> only
>> > > minimal evidence
>> > > that there are hydrated silicates in comets and
>> at least
>> > > the CI and CM CCs
>> > > very much aqueously altered and are consistent
>> with an
>> > > origin from C, B,
>> > > and G (and maybe D) asteroids.
>> > >
>> > > Larry
>> > >
>> > > > Hello Elizabeth, all -
>> > > >
>> > > > The general informal consensus within the
>> meteorite
>> > > community has been
>> > > > that carbonaceous meteorites are cometary in
>> origin.
>> > > That being the case,
>> > > > a few questions:
>> > > > 1) At what compression/temperature will CO2
>> dissociate
>> > > into Carbon and
>> > > > Oxygen?
>> > > > 2) Will Epoxi provide fine spectra data for
>> trace
>> > > elements such as calcium
>> > > > and aluminum? Platinum Group Elements?
>> > > >
>> > > > E.P. Grondine
>> > > > Man and Impact in the Americas
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
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>> > >
>> > >
>> >
>> >
>> >
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Received on Wed 24 Nov 2010 10:02:10 PM PST