[meteorite-list] Cali chondrite fell extremely cold!

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 28 Jul 2007 22:55:54 -0500
Message-ID: <05d501c7d194$5daad430$ac2ee146_at_ATARIENGINE>

Hi, Elton, List,

    But "too hot to COMFORTABLY hold" is not
very hot compared to the ablative temperature of
a minimum of 3000 C (for slow entry) to 5000, or
even 8000 C. for fast.

An iron going from 100,000 meters down to 10,000
meters, starting at 25,000 m/sec to slow to 100 m/sec is
"averaging" 12,500 m/sec in a flight that lasts less
than 6 seconds if vertical and 9-10 seconds if angled.
The extreme heating occurs during only half of the
flight. Then it gets to "fall" for 20 or 30 or 40 seconds
of cooling flight at 0 C.

    Much of the heat applied to the exterior of the iron
meteorite is "used up" melting the iron to a liquid phase,
and that heat is removed with the hot ablative melt as it
is "blown off" the surface of the iron. Perhaps as much
as 90% of the heat of ablation is transferred to the "melt."
Of course, it that keeps up, there is no iron meteorite left!

    Despite the high thermal conductivity of iron, the
heat does most of its work on the exterior, no matter
how intense. I don't disagree with your conclusion that
irons can be (may mostly be) warm, but I doubt that they
can be "hot" enough to be more than "uncomfortable."


Sterling K. Webb
----------------------------------------------------------------
----- Original Message -----
From: "Mr EMan" <mstreman53 at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Saturday, July 28, 2007 10:30 PM
Subject: Re: [meteorite-list] Cali chondrite fell extremely cold!


If memory serves--One on the Martian stones was
analyzed for its magnetic orientation and the reset of
its magnetic field post fall and was found to never
have reached 140?F deeper than 3-5 mm, indicating very
little heat transfer to the interior and only a
shallow intrusion.

During the ablation phase, heat is carried off much
like evaporative cooling is carrying off heat from
swamp coolers. Stones have a very low thermal
transfer coefficient. Irons et.al. have have high
thermal transfer coefficent as well as an ample heat
storage capacity. Given both start from a deep freeze
(no pun) it is amazing they warm up at all.

Other creditable reports mention irons as "too hot to
comfortably hold". In my mind this supports that the
thermal transfer coefficent is the key factor and that
stones will be cold and irons will be warm immediately
after landing. I don't think the atmospheric chilling
plays as much a roll as does the meteoriod's ability
to store heat in during the ablation phase. Which is
again poor for stones and high for irons.

This comes close to settling the hot vs cold debate,
in my mind.

Elton
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Received on Sat 28 Jul 2007 11:55:54 PM PDT