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

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Mon Jul 4 01:30:57 2005
Message-ID: <42C8C96A.4D95504A_at_bhil.com>

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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Received on Mon 04 Jul 2005 01:30:18 AM PDT