Hi Guys, great contributions;
Could we possibly be talking a 944 Hidalgo or something closer to an
(old friend of Larry) 733 Irmintraud ? Hidalgo specifically, Iis any
possible path from it that leads to an intersection with Earth ...
Hidalgo being historically a unicorn of a cometary/asteroid object with
low albedo
Kindest wishes
Doug
-----Original Message-----
From: lebofsky <lebof...@lpl.arizona.edu>
To: aerubin <aeru...@ucla.edu>
Cc: meteorite-list <meteorite-list@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 <meteoritem...@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
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On 5/2/12, lebof...@lpl.arizona.edu <lebof...@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: aeru...@ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html
----- Original Message -----
From: "Matson, Robert D." <robert.d.mat...@saic.com>
To: "meteorite-list" <meteorite-list@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-boun...@meteoritecentral.com
[mailto:meteorite-list-boun...@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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