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RE: (meteorobs) Temperatures of newly fallen meteorites


	I thought it was very informative, but then again, I'm probably
on the more uneducated end of the spectrum here (as meteor studies go).

Peter

-----Original Message-----
From: owner-meteorobs@atmob.org [mailto:owner-meteorobs@atmob.org] On
Behalf Of joseph_town@attdot net
Sent: Friday, March 12, 2004 2:32 AM
To: meteorobs@atmob.org
Subject: Re: (meteorobs) Temperatures of newly fallen meteorites


Doug,

Ease up. I think most of us are aware of all that.

Bill


Paul and list,

The general literature on meteorites has meteorites as being more
frequently= =20 cold than warm or hot, although all possibilities occur.
Since ablation is=20 mainly a surface phenomenon you are right that a
short atmospheric passage t= ime=20 probably leaves the meteorites core
still cold as it ramps up from generally= =20 frigid outer space.  But
keep in mind that it is really a heat transfer issu= e=20 where on one
hand you can have say a 50 kg ferro-nickel shield shaped orient= ed=20
piece of metal (I.e. the Cabin Creek fall in the 1880's which was quite
hot=20= to=20
touch) getting pretty hot due to its forced frictional interaction (i.e.
an=20 iron meteorite with a parent body having differentiated) and the
other hand,= =20 you might get an oriented elongated nosecone shaped
stone cutting though the= =20 atmosphere and getting quite frosty upon
falling.  Taking into consideration=  the=20 heat transfer coefficient
(iron is higher than stone),=20 orientation/aerodynamics (bullet shaped
minimizes frictional heating, shield=  maximizes and tumbling,=20 the
most common still tends to be cold), and weight/size (a faster fall
for=20= a=20 larger object take more heat conduction and is somewhat
analogous to the=20 question of "what is the right speed to travel in
the rain to minimize how w= et you=20 get after traveling distance X)
you can get a feel for the coldness to touch= . =20 This is undoubtably
covered in O. Richard Norton's Cambridge Encyclopedia of= =20
Meteorites, which I don't have handy at the moment.

Saludos
Doug Dawn
Mexico



I think it's unlikely that a meteorite could cause a fire.=A0 It's my=20
recollection that most meteorites are cold when the hit the ground.=A0 I
rec= all reading=20 somewhere that newly fallen meteorites=A0are
often=A0coated with frost if fo= und=20 immediately after falling.=A0=A0
=A0 Since the transit time through the atmosphere is so short, there is
not=20 enough time for heat to transfer from the surface of the meteor
into the int= erior.=A0=20 Most of the heat generated by friction is
carried away by the ablated=20 material.=A0 Consequently the average
temperature of the mass remains low an= d the=20 meteorite=A0lands cold.
=A0 I'm suspect there is some hard data in the literature on this
subject.=A0=20 Anyone have a reference? =A0 Paul Sharko


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