[meteorite-list] Cold Asteroids May Have A SoftHeart(AllendeMeteorite)
From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 16 Apr 2011 15:31:29 -0500 Message-ID: <B4294A4B1F4B4E41A2E11ACEB931AD1C_at_ATARIENGINE2> 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 ?m are reported. These data are combined with previous measurements from 0.4-1.7 ?m 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: <lebofsky at lpl.arizona.edu> To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net> Cc: "metlist" <meteorite-list at meteoritecentral.com>; "MEM" <mstreman53 at yahoo.com> 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" <sterling_k_webb at sbcglobal.net> > To: "MEM" <mstreman53 at yahoo.com>; "Richard Montgomery" > <rickmont at earthlink.net>; "metlist" > <meteorite-list at meteoritecentral.com> > 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" <mstreman53 at yahoo.com> > To: "Richard Montgomery" <rickmont at earthlink.net>; "metlist" > <meteorite-list at meteoritecentral.com> > 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 <rickmont at earthlink.net> >>> To: Ron Baalke <baalke at zagami.jpl.nasa.gov>; Meteorite Mailing List >>><meteorite-list at meteoritecentral.com> >>> 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 >>> >> ______________________________________________ >> Visit the Archives at >> http://www.meteoritecentral.com/mailing-list-archives.html >> Meteorite-list mailing list >> Meteorite-list at meteoritecentral.com >> http://six.pairlist.net/mailman/listinfo/meteorite-list >> > > ______________________________________________ > Visit the Archives at > http://www.meteoritecentral.com/mailing-list-archives.html > Meteorite-list mailing list > Meteorite-list at meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > > ______________________________________________ > Visit the Archives at > http://www.meteoritecentral.com/mailing-list-archives.html > Meteorite-list mailing list > Meteorite-list at meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list at meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list Received on Sat 16 Apr 2011 04:31:29 PM PDT |
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