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" <[EMAIL PROTECTED]>
To: "Chris Peterson" <[EMAIL PROTECTED]>;
<[email protected]>
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" <[EMAIL PROTECTED]>
To: <[email protected]>
Cc: "AL Mitterling" <[EMAIL PROTECTED]>
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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