[meteorite-list] "Flaming rocks"???

From: Frank Prochaska <fprochas_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:08 2004
Message-ID: <NDBBICFKNKHAAEEJLDALGECECHAA.fprochas_at_premier1.net>

Hello all!

In addition to these examples of meteorites being warm immediately after
landing, I remember reading several citations about meteorites forming a
layer of frost on themselves immediately after landing. It has been a
while, and I don't remember which meteorites these were.

If you look at a fresh type 3 chondrite slice, like the Bovedy L3 for
example, the heat affected zone appears to end immediately at the boundary
of the fusion crust. The matrix and chondrules out to the very edge of the
slice does not appear to be affected by heat at all - the very outside edge
appears exactly as the inside matrix and chondrules. One would expect some
effects of contact metamorphism at temperatures significantly less than the
temperature of the melting fusion crust, but the duration of the fire ball
simply isn't enough. Rock forming minerals conduct heat too poorly and take
too long to heat up. A complete slice of an iron, though, often shows a
heat affected zone as deep as 5 millimeters. This is not only visible to
the eye, but microhardness measurements as well.

Question for those with experience performing microhardness measurements on
meteorites. Are metal flakes in chondrites typically of a size large enough
to do this analysis. If so, and if the flakes are relatively homogenous,
might it be possible to measure the microhardness of flakes at the fusion
crust and then further toward the center to develop a curve similar to those
done for irons?

Frank Prochaska





-----Original Message-----
From: meteorite-list-admin_at_meteoritecentral.com
[mailto:meteorite-list-admin_at_meteoritecentral.com]On Behalf Of
FERNLEA4_at_aol.com
Sent: Saturday, February 10, 2001 8:45 PM
To: rbourlan_at_evansville.net; Meteorite-list@meteoritecentral.com
Subject: Re: [meteorite-list] "Flaming rocks"???


In a message dated 10/02/01 18:44:40 GMT Standard Time,
rbourlan_at_evansville.net writes:

<< The
 outside of the meteorite does get very hot. That's how fusion crust is
 formed. But what's been show to happen is once the material gets hot
enough
 it ablates away leaving the ice cold rock that has been floating around in
 the coldness of space for billions of years. >>

Hi Rhett and list,

ablation is very effective in removing the frictional heat energy as
material
is stripped away from the mass during flight, consequently this heating does
not penetrate to any great depth. We may not have any meteorites at all
below
a certain mass if ablation wasn't so effective.
However, regardless of how shallow or thin it might be, there must surely be
an intermediate layer between the frigid interior of the mass and the
outermost high temperature, ablating surface which could possibly be
described as "hot", but that's thoroughly dependent on interpretation.
The fusion crust itself was once right on the verge of being ablated away at
very high temperature, but it survived and then formed a blanket over any
warmed sub-layer. As retardation is reached, these outermost skins must have
been extremely hot indeed, so the big question is just how effective was the
rush of cold air during dark flight in cooling the mass before it reached
the
ground? Every fall is different, so who knows for sure?
I think there are too many reports of freshly fallen meteorites being "warm
to the touch" or "warm but not hot" to dismiss them all completely. Those
that "kick snow" on "flaming rocks" are obviously building their story for
best effect and can be dismissed easily, but I see no reason to disbelieve
others who have been fortunate enough to pick up meteorites within a few
seconds of their fall and reported them as simply warm.
The Glatton and Noblesville falls spring to mind when both fell within a few
feet of the finders, were picked up within seconds and confidently described
as warm. If the finders wanted to impress and exaggerate their story for
publicity or other reasons, adding that "it was warm to the touch" doesn't
really strike me as much of an astounding additon to what is already an
incredible story of how they were nearly beheaded by a falling space rock
(!!), so why would they bother saying it if it wasn't so?

Now, if they'd said it was warm to the touch, glowing and hissing, that's a
different story!

Cheers,
Rob Elliott....(liking his space rocks like his beer.)
http://fernlea.tripod.com/forsale.html
Fernlea Meteorites,
The Wynd,
Milton of Balgonie,
Fife. KY7 6PY
United Kingdom
Tel: +44-(0)1592-751563
Fax: +44-(0)1592-751991
Email: fernlea4_at_aol.com

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Received on Sat 10 Feb 2001 08:15:46 AM PST