[meteorite-list] Temperature of meteorites

From: JoshuaTreeMuseum <joshuatreemuseum_at_meteoritecentral.com>
Date: Tue, 23 Nov 2010 16:22:04 -0500
Message-ID: <9C6854A55BEB4F9AAB82026E5346CBF4_at_ET>

I was under the impression that it's a myth that direct friction from O and
N molecules on the surface of a meteorite create the heat that causes
ablation. I thought that ram pressure in front of the meteorite was the
main factor in generating heat. The KE and PE would create a hot shock
layer which would flow back around the meteorite causing its outer layer to
melt. I would think that friction is a minor factor, unless you're talking
about ram pressure as a kind of friction.

Phil Whitmer
-------------------

Some points for the debate:

The rapid flight through the atmosphere is very brief --
1-2 seconds. This is not much time to change the
temperature of the stone.

The rate at which the friction-generated heat is
transferred to the interior of the stone is determined
by the thermal conductivity of that rock, and rock's
thermal conductivity is very low, so low that virtually
none of the heat will affect temperatures deeper
than a few millimeters or a centimeter into the stone.

Most of that heat generated by friction on the outer
surface goes into melting rock which is then is removed
from the meteorite by on-going ablation. The molten
material stripped from the stone takes that heat with it
as it becomes the particles in the trail (which have their
own thermal evolution that does not affect the stone).
Only a small fraction is "wasted" by warming the stone
itself.

That said, thermal equilibrium of the stone is likely
achieved (or nearly) within a very short time once it
lands. Its temperature will be more-or-less whatever
it was before it encountered this obstructive planet.
Apart from some rough treatment of the surface, the
stone's temperature is the same as it always was.

So, what temperature WAS the meteoroid in the many
thousands or millions of years that it orbited the sun?

That depends on what its orbit was, or more precisely,
WHERE its orbit was and its emissivity and reflectivity
and so on. Take a look at the following chart of Meteoroid
Temperature vs. Solar Distance, supplied by MexicoDoug:
http://www.diogenite.com/met-temp.html

It is a model derived from fairly complete and reasonable
assumptions, which were discussed on this List long ago:
http://six.pairlist.net/pipermail/meteorite-list/2005-January/007521.html
This is the first of three parts; follow the links for #2 and
#3. Those with more factors to include are welcome to
refine the model, I'm sure.


Sterling K. Webb
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Received on Tue 23 Nov 2010 04:22:04 PM PST