Here you will find posts that I've selected based on their excellent content.

Pairing S-Type Asteroids to OCs (from Arkansas)

From: Mexico Doug
To: Meteorite List
Subj: Pairing S-Type Asteroids to OCs (from Arkansas)
Date: Jul 09 11:45:00 '08

http://www.sciencedaily.com/releases/2008/07/080710103903.htm The press release was confusing to me at first, highlighting the Fayetteville H4 (fall, Arkansas) meteorite. Perhaps they did because of being fresh and closer to the surface (?) in the parent body model. Not sure why the 1270 Datura family, etc., would be expected to be from the relatively rarer surface of the original parent body vs more common heat altered interior). In any caseit seems they are NOT claiming that (1270) Datura is the parent body to any of our meteorites (how could it be - don't virtually all ordinary chondrites have CRE's of floating around as meteoroids well over 1 million years?) However, it seems they are pointint out that because it is an S-type asteroid that has apparently suffered a collision only 450,000 years ago(which was shown by other researcher a studying the probabilities of members' orbits couple of years ago), it gives an opportunity to study fresher material of this most common high silicate asteroid type by telescopic spectroscopy, and they had an opportunity to take the spectra. I guess they only look at the 0.5 and 1 um peak because it is more sensitive to space weathering (?), but this isn't too clear either. (the authors didn't extend it to the typical 2.5 microns where some good stuff is visible - at least not in figure in the press release). In any case, their proposed contribution seems that they measured spectra of theyoung Datura family and compared it to ordinary chondrite spectra and got a better match than ever before helping to solve the conjecture that the common asteroid class (second only to supposed carbonaceous chondrites typed asteroids) should be paired to common meteorites. Hopefully they make a case for a trend in asteroid reflectance spectra vs. age, vs. a one hit wonder, but there still seem to be more complexities to be ironed out regarding what meteorite is appropriate to compare to what asteroid in the clan, IMO. Maybe Fayetteville was just selected because it is what they had access to... Article sounds like it will be a good one. Comments? Best wishes, Doug PS Interestingly, Wikipedia (at this moment - no doubt it will be fixed by someone reading this) says the Datura cluster formed 450 MILLION years ago and a probable source of zodiacal dust.... Maybe Wikipedia can't be trusted yet again, once the dust has settled :)

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Lunar origin of tektites

From: Marc Fries
To: Meteorite List
Subj: Lunar origin of tektites
Date: May 27 11:23:26 '05

Howdy

For the glass cooling bit, this scientist also happens to make glassware. I needed a hobby. :) The catastrophic breakdown you're talking about here isn't from rapid crystallization, but rather from uneven cooling. The finishing steps of making glassware subject the glass to rather fast cooling rates (for a glass), and the change in volume that comes with the change in temperature is enough to shatter your work. We get around that by placing the work in an annealing oven and slowly reduce it to room temperature, allowing the work to slowly change size without breaking. For lumpy shapes like tektites (or Prince Rupert's drops),

http://glassworker.bravepages.com/2003symp/competitions.html

this effect is much less important because the shape is massive relative to its surface area and roughly spherically symmetric.

Here's my thoughts on tektite formation. Silicates were melted and blasted out of the source crater into a vacuum on a suborbital trajectory. They remained molten or at least cooled very slowly, since they only had radiative cooling available to cool off. When they dropped back through the atmosphere, they simultaneously cooled on contact with the atmosphere (conductive cooling was re-established), were heated somewhat by friction, and it was shaped into ...whatever it ended up looking like. Note the competing thermal effects; which one dominates depends on the temperature of the tektite at that point, I suppose. That would explain Australian buttons - they had cooled to the point that frictional heating dominated upon atmospheric interface, and so they partially re-melted. This is in keeping with their far distance from the source crater.

The pic posted earlier of the tektite with the dimples was impressive; I'd agree that those might be from volatile exsolution. In general, however, if you jam a piece of glass in the dirt for tens of thousands of years to millions, it will turn to powder no matter how little water there is in it. I think the grooves in the edges of moldavites are a good example - radial cracks from cooling were more susceptible to devitrification. Makes 'em pretty. Now - the whole issue of volatile exsolution raises some problems. If tektites formed by condensation from a very hot, dense, short-lived silicate vapor, then there should be no volatiles left to come out of the tektites. SO - if there are bubbles, then the tektites probably formed as a liquid slush splashed out of the crater (or nearby?). BUT most tektites don't have exolution bubbles, so did most tektites form by condensation? Could there be two types - condensation and liquid-splash? It seems to me that such a thing is likely, and represents tektite formation at varying distance from the source crater center.

One thing is clear, not the least of which from earlier posts - tektites don't come from the moon.

If I can offer a suggestion about your lenticular tektite, could it have a gradient of chemical composition from its' center? That may create the features you described.

There are plenty of questions left in tektites. Good stuff.

Cheers, MDF

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When I'm 64 ... Part1 of 2

From: Mexico Doug
To: Meteorite List
Subj: When I'm 64 ... Part1 of 2
Date: Mar 28 05:02:57 '05

Bernd kindly comments:

>As a result, we're going >to get a once-in-a-millennium naked-eye asteroid show.

2029? Hola Bernd, List, No need to be handy mending a fuse when the lights are gone (Astronomers do it more passionately in the dark), we can still break out the valentine, birthday greetings and bottle of wine if you can't wait until two-oh-two-nine, no need to dream of naked-eye asteroids through the millenia of your afterlife, nor having to travel to exotic destimations for a cloudcover in that crucial hour.... You can have a date with your regular true naked-eye asteroid partner when Vesta comes by around 1 June 2007. BUT, this will not be an ordinary Vesta show! Vesta will reach 5.4 magnitude within 2 months after her 200th anniversary of discovery in 1807 29 March, and will remain naked eye visible for over a month, even at the 5.4 maximum brightness for about a week.

The good news is Vesta is not only at her opposition with us (aligned with Earth on one side of the Sun for maximum illumination and proximity), but she will be at here PERIHELION, the closest she ever gets to the Sun, being over twice as bright as other best times. And as usual, OPPOSITION means that Vesta will be raising hereself high, high in the sky wherever you be on Earth and time you make your date. So please don't forget your eyeballs for the Vesta Party Bicentennary with the naked-eye celestial body of honor, which really only will occur once in a lapse of forever!

The only bad news is there will be a full Moon at opposition, but a small amount of flexibility ojn the part of the observer with all the observation opportunity, will be fine to get the best naked view in town - your town.

And in the "Did you know..." category, Did you know that Asteroid (9969) Braille is a Vestoid HED dumb-bell shaped asteroid of over 2 kilometers long which will eventually collide with Earth, the Moon or Mars as it's orbit possibly gets more elongated by its Jupiter oppositions? If that is too long to wait, meteorite chasers get ready for this prediction: On or about 29 June 2010 there will be an HED meteor shower and a new HED strewn field loaded with fresh crusted brHED. Braille will be less than a half AU from Earth at its perihelion, well crossing within Mars' orbit, and a good telescope or CCD imager ought to let you not be blinede by Braille, a little before Earth impact from the Braille rubbish stream. Meanwhile, Braille goes to over 2/3 the distance at aphelion to Jupiter in the outer portion of the Asteroid belt before coming so, well, relatively, close.

Saludos, Doug

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A trip report by Adam Hupe for the second annual Team LunarRock Mojave hunt

From: Adam Hupe
To: Meteorite List
Subj: Cool Trip Report
Date: Dec 12 08:16:02 '04

Dear List Members,

I wanted share some details from the second annual Team LunarRock Mojave hunt.

Last year, Team LunarRock consisting of six members was successful in discovering three completely crusted meteorites in a very small strewnfield. This was a new find from a very recent fall (less than four years according to estimates provided by scientists). A name has not yet been assigned but the latest word is that it likely will be called Fort Irwin after the nearest post office box.

This years expedition was attended by nine meteorite hunters and success was demonstrated by the recovery of two new finds. Over 100 miles of hiking by each team member covering Coyote, Calico, Soda, Ivanpah and Jean dry lake beds was required in order to secure the new finds.

The first stop was Coyote Dry Lake where Steve Drummond's truck became stuck in the mud trying to access the south side of the lake. With the help of Jim Strope pushing the truck sideways and some plywood we were on our way again. After making it to the lake bed we had a difficult time searching because it was somewhat muddy after the recent rains. As can be seen in the image below, it is a very hard area to search because of all the black volcanic stones present on the surface: http://themeteoritesite.com/Coyote1.jpg

The second stop was Calico Dry Lake that produced nothing but trash. The third stop was Soda Lake which is covered by white evaporative making it impossible to search, don't waste your time.

Our fourth stop brought us to Ivanpah where we spent two days searching and had great success. The first find was made by my girlfriend, Zann. We were pleased that she found one because she came back empty handed last year. This was her very first meteorite find and weighing in at 126.5 grams, it is a nice one. It is about 80% crusted and is oriented. As far as we know, this is the very first find made on this dry lake. Not to be outdone, Dr. Ted Bunch found a completely different looking meteorite later that afternoon. I do not have the weight on Ted's find but estimate it to be about 70 grams with about 20% crust. Here is an image of Zann's find: http://themeteoritesite.com/meteorite1.jpg

If you plan on searching Ivanpah, you must get a permit and plan on hiking. No vehicles are allowed on the surface so plan on hiking at least 16 miles a day if you want to be successful. We were parked on a road just 200' onto the lake bed and were given a ticket by the BLM (watch out for white trucks!). I don't know if it is true or not but the Park Ranger told us the lake bed is highly radioactive because of tailings being dumped there sometime in the past. There is also a large fenced off area where experiments are supposedly taking place. There are some man made structures but I have no idea what is taking place here but would stay away from it so as not to raise any attention to yourself. If anybody knows anymore about this I am very curious.

In the Reed's hotel room we kicked back a couple of cold ones and took this image of the finds: http://themeteoritesite.com/Finds1.jpg

We then took a day off and toured the Valley of Fire. We ran across this scene while on route to explore the many natural wonders found in the area: http://themeteoritesite.com/ValleyFireBus1.jpg

Finally, our last stop was Jean Dry Lake bed where nothing was found except bullets. While on this lake bed we felt and heard several sonic boons. It was kind of eerie like a low level earthquake, hard to explain. It would have been interesting to see the military aircraft that generated the booms. Jean Dry Lake bed is fairly small and a lot of people target practice so be careful. Mark Jackson, now renamed "Action Jackson" after this expedition heard a bullet zing over his head because the backstop a shooter was using was inadequate. Unnerved by this we decided it was time to leave. Here is an image of Jean Dry Lake: http://themeteoritesite.com/JeanDryLake1.jpg

Hope to see more people attend next year. And if you make to Tucson we are gong to try and do a Wilcox Dry Lake hunt Saturday if the weather permits.

All the best,

------------------------------------
Adam Hupe
The Hupe Collection
Team LunarRock
IMCA 2185
raremeteorites@comcast.net

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A post by Jeff Grossman of the NomCom regarding regarding recent changes in the naming of NWA meteorites:

From: Jeff Grossman
To: Meteorite List
Subj: regarding recent changes in the naming of NWA meteorites
Date: Nov 01 01:10:43 '04

Dear all,

Last summer, I requested input from the community on two proposals under consideration by the Nomenclature Committee (NomCom). The first would change the rules by which meteorites from Morocco and surrounding areas are named, allowing well-documented meteorites to receive names other than Northwest Africa (NWA). The second would change the rules for naming paired meteorites from dense collection areas. I received many thoughtful comments from people representing all parts of the meteorite community, including scientists, dealers, collectors, and educators. These comments were reviewed by the NomCom, who, after a rather long and complicated debate, have now revised the Guidelines for Meteorite Nomenclature.

Here is what was done:

1) Meteorites from Morocco and surrounding areas may now receive unique, non-NWA names if they are very well documented as to their geographic coordinates and the circumstances under which they were found. The NomCom will judge each request individually. Meteorites with provisional NWA numbers are eligible for receipt of a non-NWA name. The names of NWA meteorites previously approved by the NomCom may NOT be altered.

2) The rules for handling paired meteorites from dense collection areas were not changed. Each new specimen will continue to receive a unique number and be subject to the existing type-specimen requirements. There was strong support in most parts of the meteorite community AND on the NomCom for changing these rules in some way that would allow the Committee to recognize pairings, which in turn would reduce the type-specimen requirements for certain paired meteorites. However, the Committee was unable to devise a practical way to do this. Of particular concern were potential legal consequences for scientists involved in disputed pairing decisions and the high administrative burden that any new system would place on the NomCom. The NomCom remains open to new ideas about changing these rules, but for now there will be no change.

The revised Guidelines for Meteorite Nomenclature are online at http://meteoriticalsociety.org/bulletin/nc-guidelines.htm.

Thanks to all of you who took the time to send me your opinions. I apologize to those of you getting this message more than once... there is significant overlap of the mailing lists I have to use.

Jeff

Dr. Jeffrey N. Grossman
Chair, Meteorite Nomenclature Committee (Meteoritical Society)
US Geological Survey
954 National Center
Reston, VA 20192, USA
Phone: (703) 648-6184 fax: (703) 648-6383

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