Hi, Larry, List,
As usual, I grabbed an idea and ran off the cliff
with it; now Larry has handed me the anvil, just
like I was the well-known cartoon Coyote. And also,
as usual, Larry is right. Must be gratifying, having
someone who has to keep posting that you are right,
Larry...
Larry said
The presence of hydrated silicates on asteroid
2 Pallas dates back to the early 1980s
Larry is referring modestly to:
Feierberg, M. A.; Larson, H. P.; LEBOFSKY, L. A. (1982).
"The 3 Micron Spectrum of Asteroid 2 Pallas.".
Bulletin of the American Astronomical Society 14: 719.
Unfortunately, the ADS system only gives the page with
the title at the bottom of the page and then cuts off the
article which starts on the next page...
Although, in my defense, I could cite:
http://www.lpi.usra.edu/books/AsteroidsIII/pdf/3031.pdf
in which there is a table that shows Pallas (B-class)
with ZERO absorption in the 3-micron band (water,
in other words). Also has "Lebofsky, L. A." as an author.
Links to all or part of Larry's 304 articles:
http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?return_req=no_params&author=Lebofsky,%20L.%20A.&db_key=AST
Looking for water (or anything like it) by peering through
the wet sodden atmosphere of Earth is a chancy business;
the data needs to massaged. I'm not suggesting that the
data isn't reliable, just that it's likely to have fuzzy edges.
Just an abstract, but summarizes well:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4731CCX-DV&_user=10&_coverDate=12%2F31%2F1983&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_searchStrId=1720558577&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b3a90d3f66329ead2085b10dd7dbde6b&searchtype=a
"High resolution spectroscopic observations of
asteroid 2 Pallas from 1.7-3.5 μm are reported.
These data are combined with previous measurements
from 0.4-1.7 μm to interpret Pallas' surface mineralogy.
Evidence is found for low-Fe-2+ hydrated silicates,
opaque components, and low-Fe-2+ anhydrous silicates.
This assemblage is very similar to carbonaceous chondrite
matrix material such as is found in type CI and CM
meteorites, but it has been subjected to substantial
aqueous alteration and there is a major extraneous
anhydrous silicate component. This composition is
compared to that of asteroid 1 Ceres. Although there
are substantial differences in their broad band spectral
reflectances, it appears that both asteroids are genetically
related to known carbonaceous chondrites."
These folks thinks it's drier than Larry's studies:
Sato, Kimiyasu; Miyamoto, Masamichi; Zolensky, Michael E.
(1997). "Absorption bands near 3 m in diffuse reflectance
spectra of carbonaceous chondrites: Comparison with asteroids"
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1997M%26PS...32..503S&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf
More new looks. These guys think Pallas is smaller
than previously thought, they say, and they have refined
that strange shape (very nice graphics):
http://www.eso.org/sci/activities/santiago/projects/PlanetaryGroup/journal_club/slides/ESO.JournalClub-2007.08.14-BenoitCARRY.pdf
And if it were smaller but the mass is correct, then Pallas'
density would be higher. That would have implications
for trying to mentally reconstruct it...
And of course in Larry's second reference, Pallas is
bigger than we thought and hence less dense. This
suggests we have a way to go in order to pin this down.
It should be explained (if anybody is still following this)
that Pallas is not easy to observe -- it dark and its
eccentric orbit carries it far enough away to be very
dim except at those short intervals when it's close to
the Sun and the Earth passes it at its nearest approach.
Is there a general trend toward our perceiving primitive
meteorites as drier than we thought?. See:
"Primitive Meteorites Depleted in Volatiles "(press release)
quotes from Phil Bland and Monica Grady:
http://www.pparc.ac.uk/Nw/meteorite.asp
Obviously, Pallas is not "dry" in the same sense as the
Moon or Mercury and I was wrong to imply that,
although it might be less than 10%. The Sato paper
suggests it's more like Renazzo than like Larry's
suggestion of Murchison, or about half as "wet."
5%?
There's no substitution for actually going there and
looking it over for yourself, which someday we'll be
able to. Until then, we'll have to have fun guessing
and peeking through the wet murk of Earth.
Sterling K. Webb
---------------------------------------------------------------------------------
----- Original Message -----
From: <[email protected]>
To: "Sterling K. Webb" <[email protected]>
Cc: "metlist" <[email protected]>; "MEM"
<[email protected]>
Sent: Saturday, April 16, 2011 11:27 AM
Subject: Re: [meteorite-list] Cold Asteroids May Have A
SoftHeart(AllendeMeteorite)
Hi Sterling
Sorry for taking so long in responding, but I am still catching up from
being out of email access for three days this weekend and I missed this
one.
The presence of hydrated silicates on asteroid 2 Pallas dates back to the
early 1980s and has been confirmed numerous times and spectrally matches
Murchison.
So unless you imply low water as being only about 10% water by mass,
Pallas is not dry!
Larry
http://www.lpi.usra.edu/meetings/LPSC98/pdf/1310.pdf
http://adsabs.harvard.edu/abs/2008DPS....40.2204S
It shows signs of olive and pyroxene,
I meant OLIVINE, of course.
when we got their...
and THERE. Spell checkers don't catch
these mistakes, only working brains, so...
New rule: No more Posts after midnight.
Sterling K. Webb
---------------------------------------------------------
----- Original Message -----
From: "Sterling K. Webb" <[email protected]>
To: "MEM" <[email protected]>; "Richard Montgomery"
<[email protected]>; "metlist"
<[email protected]>
Sent: Thursday, April 14, 2011 1:21 AM
Subject: Re: [meteorite-list] Cold Asteroids May Have A
SoftHeart(AllendeMeteorite)
Hi,
Way too much stuff here to deal with all,
but I have a word about 2 Pallas as a
"Carbonaceous parent body."
Pallas has a silicate spectrum. A great many
bodies do. It shows signs of olive and pyroxene,
with low iron and water. If it resembles any
Carbonaceous chondrite, it's a CR with no
hydrated minerals or very little.
Pallas is very dark, with an albedo of 12%-14%,
almost as dark as our moon, whose albedo is
7% to 8%. Yes, when we look at the Moon
at night, it looks BRIGHT, but in reality, the
Moon is about the color and reflectivity of
a huge lump of black anthracite coal.
The fact that it doesn't look like a lump of coal
in pictures taken on the Moon or looked to the
astronauts as a very light grey demonstrates
the ability of the human mind to scale image
intensity to the Earth norm and to expose film
to achieve similar results.
Pallas is a little brighter than the Moon but
some darker than Mercury which is about 15%
to 16% albedo. Of course, if a human eye was ON
Mercury, the planet would appear to us as blazing
white under sunlight more than 2.5 times brighter
than here at Earth.
The density of Pallas is about 2.8. The similar
sized Vesta is 3.43, our Moon 3.35, Mercury . For
comparison, Earth's crustal rocks, mostly silicates,
have a mean density of about 3.0. It seems unlikely
that Pallas has an iron core. Like the Moon and
Mercury, it seems to be essentially waterless.
The spectral "classifications," both the Tholin and
the 2Mass, classify a great many asteroids as varieties
of "Carbonaceous," but we see far fewer Carbonaceous
meteorites than they see asteroids!
We spent many decades trying to analyze the surface
of the Moon spectroscopically, it being so conveniently
close and all, but none of it told us that much about
what we'd find when we got their. Similarly, spectral
studies of Mars from Earth are largely forgotten for
the same reason: they were wrong.
I expect Pallas to be excessively dry and waterless,
made of excessively dark rock, primitive in composition,
likely has little plagioclase on the surface, probably
isn't "differentiated" and lacks basalt melts. But hey!
I'm just guessing.
There is a chance that we may get a look at Pallas.
When the Dawn mission is mission is finished at Ceres,
if all systems are functioning and fuel supplies are
within parameters, it COULD be sent on a flyby of
Pallas. Dawn couldn't orbit it, but it could grab a lot
of lovely snapshots on that pass.
Of course, we'd have to get it funded by Congress...
Groan.
Sterling K. Webb
--------------------------------------------------------------------------
----- Original Message -----
From: "MEM" <[email protected]>
To: "Richard Montgomery" <[email protected]>; "metlist"
<[email protected]>
Sent: Wednesday, April 13, 2011 9:31 PM
Subject: Re: [meteorite-list] Cold Asteroids May Have A Soft
Heart(AllendeMeteorite)
Let me play politician and ask to "revise and extend my remarks".
There are
asteroid gurus on the list who are more likely able to address this
and I'd like
to hear from them. Your theory/question is partially in the right
direction so
let me re-frame it. I believe we have "likely" detected all the
existent
asteroids in our inner solar system which are large enough to have
formed
basalt/cores--aka differentiated. That size is hard
overlook(100-300km
minimum?). I read somewhere that as many as 12-20 major/minor planets
would
have formed in the early solar system that are no longer with us as
major/minor
intact bodies.( i.e. absorbed or ejected)
As to meteorite parent bodies, what we have yet to inventory and, for
which we
have not had a specimen drop by Earth for comparison, are these long
ago
disrupted bodies. These bodies which now are represented only by
minor,
irregular, slivers, slices, and rubble piles within certain swarms of
asteroids
in different sectors of the solar system.
There is a "diogenite-like" spectrum coming from an outer-belt
asteroid whose
orbit proves it cannot be related to Vesta. I mentioned the caveat
that there
may be some remnants of asteroids which were differentiated in the
early solar
system and for whatever reason are no longer in tact. We may only
have a
fraction of the original large body such that while we have located
all the
differentiated intact ergo larger asteroids, we may need to be
looking for
shards of former bodies to match meteorites from our collections. The
reason
all our "HED"s are from Vesta is probably that Vesta is on our "mail
route" and
quantum transport from Vesta to Earth is a favorable happenstance.
"1459 Magnya: Orbits in the outer main belt, too far from Vesta to be
genetically related. May be the remains of a different ancient
differentiated
body that was shattered long ago." Spectrum is diogenite-like
Another candidate which may be the source of olivine-diogenites but is
a chunk
off Vesta:
"2579 Spartacus - contains a significant portion of olivine, which may
indicate
origin deeper within Vesta than other V-types."
See list at:
<http://en.wikipedia.org/wiki/V-type_asteroid>
<http://en.wikipedia.org/wiki/4_Vesta>
Pallas and its family of asteroids is certainly a candidate for one of
the
Carbonaceous parent body, even thought it shows no major excavations.
"2 Pallas is a large and most certainly differentiated body but lacks
evidence
of a deep
excavation and its spectrum shows carbonaceous chondrite affinities.
However
75% of the astrtoids out there whose spectra we've measured fall in
the C or
Carbonaceous class."
<http://en.wikipedia.org/wiki/2_Pallas>
<http://en.wikipedia.org/wiki/Carbonaceous_chondrite>
Also in my reading there is good indication that the Martian moons are
captured
carbonaceous asteroids
<http://en.wikipedia.org/wiki/Moons_of_Mars>
Asteroid types More than I can retain in my head:
<http://nineplanets.org/asteroids.html>
<http://en.wikipedia.org/wiki/Asteroid_spectral_types>
* C-type, includes more than 75% of known asteroids: extremely
dark
(albedo 0.03); similar to carbonaceous chondrite meteorites;
approximately the same chemical composition as the Sun minus hydrogen,
helium
and other volatiles;
* S-type, 17%: relatively bright (albedo .10-.22); metallic
nickel-iron
mixed with iron- and magnesium-silicates;
* M-type, most of the rest: bright (albedo .10-.18); pure
nickel-iron.
* There are also a dozen or so other rare types.
Read more about Asteroids l Asteroid facts, pictures and information
by
nineplanets.org * C-type, includes more than 75% of known asteroids:
extremely dark (albedo 0.03); similar to carbonaceous chondrite
meteorites; approximately the same chemical composition as the
Sun minus
hydrogen, helium and other volatiles;
* S-type, 17%: relatively bright (albedo .10-.22); metallic
nickel-iron
mixed with iron- and magnesium-silicates;
* M-type, most of the rest: bright (albedo .10-.18); pure
nickel-iron.
* There are also a dozen or so other rare types.
Read more about Asteroids l Asteroid facts, pictures and information
by
nineplanets.org
Meteorites and their Parent Bodies 2nd Edition. Harry Mc Sween which I
think us
a google book online.
Elton
----- Original Message ----
From: Richard Montgomery <[email protected]>
To: Ron Baalke <[email protected]>; Meteorite Mailing List
<[email protected]>
Sent: Wed, April 13, 2011 8:39:46 PM
Subject: Re: [meteorite-list] Cold Asteroids May Have A Soft Heart
(AllendeMeteorite)
Ron and List,
This new evidence fits exactly into the recent question I posted,
'Vesta,
for sure?'
I only heard back from Elton (thanks, sincerely!) and yet now with
this
hypothesis, my question lingers as to the absolute recognition of
parent
bodies, with my query as to the yet-undiscovered potential pairings
of
undiscovered asteroids.
MEM pointed out that the largest asteroids (aka Vesta etal) have
already
been located, with tell-tale impact and reflective signatures that
rule out
other parents for our HEDs.
My new question, neophyte layman as I am, is:
Does this new data/theory bring my initial question about
Vesta-for-sure-as-parent-for-HEDs back into play?
-Richard Montgomery
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