[meteorite-list] Temperature of meteorites

[MEM]

I recall an objective, quantified study of temperature history in meteorites 
which proved something about the hot/cold debate and internal temperatures.  One 
of the Martians ( Zagami?) was studied for "magnetic domain orientation" in that 
the evidence of a martian paleo-magnetic field might have been preserved.  It 
was.  The study relied on the fact that the orientation of magnetite's "magnetic 
domains" would be reset if the meteorite had been heated above 165°(c or F ?).  
They had not if below 5mm

What was discovered ,was that the magnetite domains more than 5mm deep had not 
been reset to Earth's magnetic field.  What this says for internal temperature 
in this meteorite: any and all heat build up to give the surface a "hot touch" 
is restricted to roughly a zone 3-5mm deep.  The thermal conductivity of 
silicates is low and as was said ablation is a very effective means of keeping 
the internal core temperature from rising at the expense of mass raised to the 
melting point and whisked away.

I do believe that iron meteorites, having a higher heat conductivity 
co-efficient will retain much more re-entry generated heat and could feel warm 
several minutes.  Otherwise I tend to believe the vignette reports such as those 
of the firemen in New England that reported a rind of frost forming on the 
broken meteorite as it lay under the dinning room table.

Elton





----- Original Message ----
> From: "almitt2 at localnet.com" <almitt2 at localnet.com>
> To: meteorite-list at meteoritecentral.com
> Sent: Tue, November 23, 2010 7:00:11 AM
> Subject: Re: [meteorite-list] Temperature of meteorites
> 
> Greetings listees,
> 
> ahhh the hot/cold debate rears it's head again. I  appreciate Bernd's list of 
>falls that seem to indicate warm more so than cold  but there are many factors 
>to consider when compiling data. In Bernd's list, how  many of these warm 
>specimens were observed by laymen?? Often there are other  factors to consider 
>and layman's observations can be often wrong. If a black  specimen sits for very 
>long in the sunlight it will absorb warmth and appear  warm or hot.
> 
> Things to consider, Fall dynamics. The space shuttles build  up a lot of high 
>heat during decent through the atmosphere. Shuttles have to  cool for a while 
>after landing. Meteoroids, depending on their fall speed, only  pass through the 
>atmosphere for a short period of time (seconds before dark  flight) and don't 
>have suffiecent time to build up heat. The ablating process  often removes the 
>molten material as the object falls keeping the specimen more  or less at cold 
>space temperature.
> 
> Catching up or head on collision with  Earth effects speed and temperature and 
>fall dynamics. Spinning or stable flight  (possible oriented specimen) affects 
>temperature. Size of specimen and retention  of cold from space.
> 
> One thing for certain when thinking about the  hot/cold debate. If meteoroids 
>are heated up molten when they fall, then the  chemistry would be altered and 
>isotopes reset. Most meteorites don't have high  heat alteration from falls or 
>our ability to study them would be impossible. The  age would be reset from the 
>heating. The study of meteorites is the study of un-altered specimens from our 
>solar systems past!!
> 
> I tend to be a cold  when they land believer but think a few can come down 
>oriented and there is time  for them to absorb some heat from the fall. Nininger 
>investigated several falls  seen by laymen that were frosted over but he was 
>efficient at determaining facts  based on the story tellers.
> 
> There are a lot more considerations and facts  about falls that are probably 
>still not understood at this time. Fall dynamics  are difficult to study unless 
>you have an expert with equipment the second the  fall occurs at the site when 
>it happens.
> 
> My hot and cold  worth.
> 
> --AL Mitterling
> Mitterling  Meteorites
> 
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