[meteorite-list] Meteorites - warm or hot to the touch?

From: Mark Langenfeld <mlangen_at_meteoritecentral.com>
Date: Mon Jul 4 09:36:52 2005
Message-ID: <002601c5809d$66682810$459f7644_at_D5KDJZ51>

Eighty-eight years ago today, a 104 kg. L6 was observed to fall on a warm,
humid July 4th evening in Colby, WI (celestial fireworks!). When recovered
shortly thereafter, the two main mass pieces were found to be covered with
frost.

Mark

----- Original Message -----
From: "Sterling K. Webb" <kelly_at_bhil.com>
To: "Chris Peterson" <clp_at_alumni.caltech.edu>;
<Meteorite-list_at_meteoritecentral.com>
Sent: Monday, July 04, 2005 12:30 AM
Subject: Re: [meteorite-list] Meteorites - warm or hot to the touch?


> Chris,
>
> Read:
> <http://six.pairlist.net/pipermail/meteorite-list/2005-January/148342.html>
> for
> internal ambient temperatures on space.
>
> During ablation (which usually removes 90% or more of the rock, leaving
> the
> inner core only) surface temperatures are 1800 degrees C and up, depending
> on
> angle and initial velocity. Peak temperatures are about 20,000 degrees C.
>
> It requires at least 150 gee's (at 45 degrees) to decelerate a
> meteoroid to
> Earth's surface at median entry velocities. Tunguska air-burst at 200
> gee's
> calculated. Fragmentation and crushing are far more likely, and the
> fragments
> usually vaporize instantly, anyway.
>
> Crushing strength of chondrites is a measly 0.1 to 10 bar; achondrites
> 62 to
> 2700 bar; irons to 4000 bar, but they're very brittle and come apart way
> below
> those lab values. Calculation of crushing in actual observed fireballs, 30
> to
> 50 bars.
>
> The smaller the object is, the cooler on arrival, but even the tiniest
> Pultulsk or Holbrook has crust, or if it's small enough, IS crust.
> Anything that
> has or had crust has reached the melting to boiling point of rock.
>
> It won't cool if still in hypersonic flight, and anything that is in
> hypersonic flight when it reaches the ground won't survive impact, a
> narrow
> window if crushing strength is less than 10 bar.
>
> Impactor vaporizes when impact speed approaches the speed of sound in
> the
> impacting body. Measurement of the speed of sound in meteoritic stones (as
> low
> as 600 m/sec) much less than in well consolidated Earth rocks.
>
> Some are cool, some are warm, but not very cold and not very warm.
>
> Sterling K. Webb
> --------------------------------------
> Chris Peterson wrote:
>
>> Hi Elton-
>>
>> I'm curious about the basis of your assertion that physics suggests a
>> typical meteorite should be hot on the outside and cool on the inside. I
>> would expect a large stone (or iron) to have an internal temperature
>> similar
>> to what it was at in space, which can vary from around -100?C to +60?C
>> depending on the parent's albedo and surface properties. As the object
>> gets
>> smaller, its passage through the atmosphere becomes more important in
>> determining its final temperature. Something fist sized, for instance,
>> will
>> have probably equilibrated its temperature to the atmosphere during most
>> of
>> its fall (-40?C is a good value for this), and then begun warming from
>> the
>> outside during the last minute in warmer air. Depending on the thermal
>> conductivity of the material, I think it will feel somewhere between
>> ambient
>> and slightly cool. I believe that the conditions leading to a warm or hot
>> exterior are not common.
>>
>> Chris
>>
>> *****************************************
>> Chris L Peterson
>> Cloudbait Observatory
>> http://www.cloudbait.com
>>
>> ----- Original Message -----
>> From: "E. L. Jones" <jonee_at_epix.net>
>> To: <Meteorite-list_at_meteoritecentral.com>
>> Cc: "AL Mitterling" <almitt_at_kconline.com>
>> Sent: Sunday, July 03, 2005 5:42 PM
>> Subject: Re: [meteorite-list] Meteorites - warm or hot to the touch?
>>
>> > I personally believe the meteorite surface is very warm slightly hot on
>> > most falls while the interior is very cold. That is what the physics
>> > say
>> > should be. While metal/iron is a good heat conductor,
>> > olivine/silicates
>> > is/are not, and it should take a longer time for the two temperature
>> > extremes to neutralize in a stony fall. Ironically, an iron might
>> > actually
>> > take longer to cool down than a stone becasue it could theoretically
>> > store
>> > up more of the ablation heat internally than a stony could.
>>
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>
>
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Received on Mon 04 Jul 2005 09:36:34 AM PDT