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(meteorobs) re: meteorite temperatures

Hi,

A few days ago there was some discussion on this list about free fall
temperatures of meteorites and reports of warm to the touch fresh falls. I
have a partial explanation  to offer.

Physically, these hot meteorites upon impact should not be possible. During
dark flight the meteorites' velocity is well below the speed of sound and
the airflow should actually cool the object rather than warm it. Still there
are many of such reports (but, please note, also some of icy cold, even
frost covered meteorites!!) so we should not neglect it. Perhaps something
else is going on.

But there also is a very down to earth explanation of at least some of these
reports. I literally touched upon this some years ago when I photographed a
fussion crust covered fragment of Mbale. For that purpose I placed it in
bright sunlight and made my photographs. When I took up the fragment I
almost dropped it again: it felt very warm and my initial response was to
retract my fingers in order not to burn them. A second touch reveiled the
meteorite to be warm, but not as "hot" as my initial nerve system reaction
suggested. Mind you, this was some 2 years after this fragment had
fallen.....

The solution is simple. Fussion crusts are black. They absorp sunlight and
radiate that as warmth. Only a few minutes of exposure to a summer sun is
enough to warm it noticably. It is the same effect well known to those who
go sit on a dark painted park bench in summer, or tread on tarmac bare feet
in summer.

This explains at least some of the reports, although perhaps not all.

By the way, in my task of checking meteorite falls and finds reported to the
Dutch Meteor Society I have had a report of an object being "hot too the
touch" upon a presumed fall once or twice, most recently last October (with
the dog reportedly burning its nose) - but in all cases, the material was
not a meteorite but terrestrial. Imagination does a lot, especially if
people expect something to be hot.

- Marco Langbroek

---
Marco Langbroek                    private: marco.langbroek@wanadoodot nl
Leiden University                     work: m.langbroek@arch.leidenunivdot nl
Faculty of Archaeology
P.O. Box 9515
NL-2300 RA Leiden
The Netherlands

"What seest thou else
  In the dark backward and abysm of time?"

William Shakespeare: The Tempest act I scene 2
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