[meteorite-list] Its official! NWA 6291 "The King ofAngrites"forsale - AD
From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 24 Jul 2010 00:28:51 -0500 Message-ID: <CF52E38CCFDF499090989B78C1E616B1_at_ATARIENGINE2> Actually, I was not addressing the specific question of the origin of this angrite (or any angrite), but the more general problem of the "universal assumption that every sizeable body in the solar system currently resides at the same address where it accreted originally." If things move around, it complicates the picture considerably. I used Vesta as an example of a body that can't have accreted in place. If there is only enough available iron at 1.5 AU for Mars to accumulate a core that is only 8% of its volume), how could Vesta, at 2.35 AU, have accumulated enough iron for a core 17.5% of its volume, or 56% of its original, uncratered diameter? The Earth has a core of 17% of its volume, or just a hair less than Vesta. Mercury has a core that's 43% of its volume. Both the Earth and Mercury have acquired part-corers from encounters with impactors though. Iron is a moderately refractory element. It will be vaporized in the solar nebula only relatively close to the Sun. The temperature will drop by the square of the distance out in the protoplanetary disc and iron will soon condense into the materials from which grains will form, get sticky, form particles, accrete, etc. How you gonna get that much iron vaporized out at 2.35 AU? The answer to that question is the same one I gave before: No Way. And for the same reason. If you want to know what should accrete out there, you can compare Vesta to Ceres. Ceres is in essentially the same region as Vesta, at 2.7 AU compared to Vesta's 2.35. AU. Ceres seems to have no core at all, although Ceres is certainly large enough to have differentiated. Ceres likely did accrete in place from rock and ice, as it is the largest body in the asteroid zone, six times the volume of the original, uncratered Vesta. We can identify Lunar and Martian meteorites only because we have composition data gathered by humans and robots. That's the only reason. Without a sample or a set of readings from Mercury, or Venus, or anywhere, the means of reasonable proof are absent. When the Dawn mission gets to Vesta, we will likely be able to nail down the HED identification with that body. I quote the mission parameters: "This mission was designed to verify the basaltic nature of Vesta inferred both from its reflectance spectrum and from the composition of the howardite, eucrite and diogenite meteorites believed to have originated on Vesta." Failure to find the expected HED terrain on Vesta would be.... interesting. Dawn will be the first test of the entire effort to "reason out" parent bodies. It will provide evidence where they has mostly been speculation. The paper you cite (by Chambers) is a good summary of the problems in planetary formation theory. There are lots of those. I used Vesta as an example because it's an obvious example of the sort of thing he discusses in the section on "planetary embryos." Vesta would be at the smallest end of their size range -- not too hard to toss around. Until there is evidence enough to settle the question, it remains speculation. we've had definitions of Science and of Faith on the List recently. Let me add another one more: Speculation. Speculation is what you do while you're waiting for evidence, because there isn't enough evidence yet for proof. Sterling K. Webb ------------------------------------------------------------------------------- ----- Original Message ----- From: "Shawn Alan" <photophlow at yahoo.com> To: <meteorite-list at meteoritecentral.com> Sent: Friday, July 23, 2010 10:33 PM Subject: [meteorite-list] Its official! NWA 6291 "The King ofAngrites"forsale - AD Hello Sterling and Listers, Sterling, thank you for your input about Angrites "might" have a connection with Mercury by saying Vesta quote un quote...... "Vesta did not .....form where it is. No Way." Know I am kinda confused with Vesta and your connection or lack of connection to this topic, but I am going to make an educated guess of why you might have suggested Vesta in the first place. This whole topic pulls from Angrites and the possible connections they might have with Mercury. I am going to zero in on one meteorite, NWA 2999 because it seems that there has been more research done on this meteorite compared to other Angrites. One observation of why some scientist feel that NWA 2999 "might" be from Mercury is that NWA 2999 meteorite has gone through a vertical tectonics process, which occurs on Earth and Mercury. In addition to this vertical tectonic process....... Papike et al. [9] suggested that angrites might be samples from Mercury based on volatile depletion, and systematics of plagioclase compositions and Fe/Mn ratios in mafic minerals. http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1344.pdf Now Sterling, is this the reason why you brought Vesta into this equation, because its a differentiated body and the vertical tectonic process might have happened on Vesta? Or its because you feel that Vesta some how moved from one side of the hood to the other side because of the iron core being too big for where Vesta is located at? Lets change the topic and focus on your statement on how you feel about Vesta, quote un quote ...... "Vesta did not .....form where it is. No Way." Now this would be a perfect example to use this quote Greg Lindh....... This reminds me of a quote by Mark Twain. The quote follows: "There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact." Something to think about.... Iron meteorites tell their own tale. These meteorites come from asteroids that became hot enough to melt and differentiate. The most plausible source of heat was the decay of short-lived isotopes, especially 26Al. Melting must have occurred while was still abundant, which means these asteroids took something like 2 Myr to form [19,20]. Why did some asteroids melt when others did not? Presumably, different stages of planet and asteroid formation occurred concurrently in the same region of the nebula. Some objects formed earlier than others, and their subsequent thermal evolution was different as a result. http://groups.csail.mit.edu/mac/users/wisdom/extrasolar/chambers.pdf I think this pulled abstract could explain your educated guess of why you think Vesta had accreted somewhere else besides where it is :) My guess is that when differentiation occured, that with some parent body the process was more prevalent because there might have been an abundant amount of 26Al , which this short lived isotope produces alot of heat which would be a good environment for differentiation to take place aka in Vesta :) but thats my suggestion and some science to back it up :) Shawn Alan [meteorite-list] Its official! NWA 6291 "The King ofAngrites"for sale - ADSterling K. Webb sterling_k_webb at sbcglobal.net Thu Jul 22 17:03:44 EDT 2010 Previous message: [meteorite-list] Its official! NWA 6291 "The King of Angrites"for sale - AD Next message: [meteorite-list] Its official! NWA 6291 "The King of Angrites" for sale - AD Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] Martin, Jason, Shawn, &c., The fly or flaw in the ointment, the paper, and the responses is an unspoken but apparently universal assumption that every sizeable body in the solar system currently resides at the same address where it accreted originally. What about a body that accretes in the 0.50 AU block, then moves 'way up the street and out to the 2.35 AU neighborhood? Like say, Vesta. Now, I'm not saying Vesta did that, you know, fled from the 'hood and moved to the suburbs... I just saying Vesta did not form where it is. No Way. Models that "fit" Vesta propose a iron core of about http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2129.pdf 300 kilometers out of an original spherical body of 540 km. diameter. Such a body HAS to have accreted much, much closer to the Sun. I repeat, No Way. So, isotopic data that tell you where a body accreted MIGHT tell you everything you need to know about the place or it MIGHT tell you nothing of any use whatsoever. Even the old notion about the distribution of iron cores in the inner solar system is wrong. Decades ago, we assumed bigger iron cores in close, getting smoothly smaller as you moved out from the Sun. Then, we discovered that Venus' core is proportionally much smaller than the Earth's, and that Mars core is puny. Then, when we moved to the theory of the Moon being formed by a giant "impact," or graze, or embrace, all the models said we had two cores -- our original core and the core captured from the big proto-Moon. Mercury too shows evidence of such a collision (although no moon resulted). All of a sudden, Venus and Mars have "normal" cores. The Earth is cheating -- it's packing an extra halfcore in its hip pocket, and Mercury has two cores-worth of core. Venus and Mars that are normal respectable planets, and Earth and Mercury are "core-snatchers." A simple question like "what should a meteorite from Mercury be like?" is not a simple question. First, if Mercury suffered a giant impact early on, then its present crust (and upper mantle and maybe more) is derived from the impacting body. And that Big Whacker accreted... where? Nearby? Faraway? In-between? Then, there is the case of a parent body of some size blasted off the ORIGINAL primordial crust (and mantle) of Mercury by the giant impact, finding a new orbit, and providing enigmatic meteorites for the next billions of years. That original Mercurian crust could have been quite different from the present crust. As Jason pointed out, there were a gaggle of large differentiated bodies in the early system. I go with the "hundreds" rather than 30-40; see the work by SwRI that suggests 100+ of them from the inner solar system ended up in the Asteroid zone. The Zone is made up of "natives" and a horde of refugees, which could have accreted pretty much anywhere and will each have a unique formation history all their own. Present arguments are somewhat simple-minded. It's going to take centuries to sort out the life history of every body big enough to bother with. It's going to be fun. Sterling K. Webb -------------------------------------------------------------------------------- ----- Original Message ----- From: "Martin Altmann" <altmann at meteorite-martin.de> To: <meteorite-list at meteoritecentral.com> Sent: Thursday, July 22, 2010 6:00 AM Subject: Re: [meteorite-list] Its official! NWA 6291 "The King ofAngrites"for sale - AD Huh, I found even a paper, which postulates, that the HEDs are from Mercury and the angrites from Venus.... http://www.lpi.usra.edu/meetings/otp2004/pdf/3012.pdf ;-) Martin -----Urspr?ngliche Nachricht----- Von: meteorite-list-bounces at meteoritecentral.com [mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Jason Utas Gesendet: Donnerstag, 22. Juli 2010 11:27 An: Shawn Alan; Meteorite-list; Adam Hupe Betreff: Re: [meteorite-list] Its official! NWA 6291 "The King of Angrites"for sale - AD Shawn, Well-said - But I can't emphasize enough the fact that such large bodies existed in large numbers in the early solar system. That much is obvious from the large numbers of ungrouped (and grouped) differentiated achondrites that we have in our collections here on earth, as well as from all various types of iron meteorites, which represent the cores of diffeentiated planetismals. All in all, we have meteorites that suggest well over 30-40 such bodies in the early solar system, and computer-run models in some cases suggest hundreds of such bodies. http://www.ucmp.berkeley.edu/education/events/cowen1d.html http://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#For mation_of_planets Note that wikipedia suggests 50-100 such bodies. I wouldn't usually reference wikipedia for something like this, but see references 35-36 for the article - that's actually a decent estimate that's been backed up by some serious work done by experts -- it's not just a crap wikipedia reference. So, angrites may be from Mercury. If we say that, regardless of their composition and history, they just needed to be from a large planetismal capable of some metamorphic activity, then we've got a 1/50 to 1/100 chance that angrites are, in fact, from Mercury. The trouble is that their chemistry and age suggest that they're not from Mercury. I agree. They *might* be from Mercury. And yes, some smart people have said that they *might* be from Mercury. But it seems to me that this article is being deemed credible because of its authors, and not because of what it actually says. >I do not refute Melinda Hutson's article that was never peer reviewed >and contains several errors according to the classifying scientists. I asked scientists about the article and they stated, it is obvious that she didn't read the original peer reviewed abstract carefully, even mistaking the type of petrology that was discussed using formulas that simply do not apply to the texture NWA 2999 exhibits. I'd like to know what these errors were, and how the error might have affected her conclusions. Perhaps Adam or someone else would be willing to explain her errors and how they suggest that angrites are actually from Mercury. Seems like this is the perfect sort of topic for the list... Regards, Jason ______________________________________________ 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 Previous message: [meteorite-list] Its official! NWA 6291 "The King of Angrites"for sale - AD Next message: [meteorite-list] Its official! NWA 6291 "The King of Angrites" for sale - AD Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] More information about the Meteorite-list mailing 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 24 Jul 2010 01:28:51 AM PDT |
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