[meteorite-list] Re: hot meteorites (on other Lists)

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:09 2004
Message-ID: <20010213031654.73605.qmail_at_web10406.mail.yahoo.com>

For those that are interested, here is a URL that is a
compilation of recent discussions (on another List)
regarding this subject:

<http://groups.yahoo.com/group/meteorobs/messagesearch?query=hot%20meteorites>

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Date: Mon, 12 Feb 2001 18:52:38 -0700
From: Mike Mazur <mazur_at_geo.ucalgary.ca>
To: Sharkkb8_at_aol.com
Cc: meteor.dealer_at_gte.net,
meteorite-list_at_meteoritecentral.com
Subject: Re: [meteorite-list] hot meteorites

A chondritic meteorite in freefall has a terminal
velocity of something on the order of 80 m/s (10cm
diameter, sg=3). Time of dark flight is then on the
order of 3 minutes from a height of 15km. If you're
creative you could even get it up above 10 minutes for
low density material at greater heights. The fusion
crust is typically only a fraction of a mm in
thickness with very little heating interior of the
crust. Surely 3 to 10 minutes is long enough to cool a
silicate melt of such a thickness to the ambient air
temperature. Not having done it myself I'd be curious
to know if a naked skydiver would be chilled to their
core if they jumped
from only 3 or 4 km. I'm sure that they'd be
shivering, at least.
Something to try I guess. In the case of an object
that retains a significant component of its entry
velocity, however, things would be different due to
frictional
heating occuring until the time of impact. Irons,
having high thermal conductivities and potentially
lower terminal burst altitudes, could conceivably
under
some circumstances retain some heat but this is likely
a rare occurence.

Mike Mazur

Sharkkb8_at_aol.com wrote:

> << There are too many reports of meteorites being
hot to the touch and singing objects to say they are
cold when they fall...........There was even a stone
from the Portales Valley fall with a piece of plastic
melted to it after landing on a plastic object. >>
>
> I would think that the exterior of the stone would
be hot at the moment of impact, but that the
interior99.9% of the rock, which is still essentially
deep-space frozen at that point, would cool that thin
exterior down extremely quickly (contraction cracks?).
 It would seem plausible enough that the Portales rock
could melt some plastic upon immediate contact with
it, but I'd
bet that the chance of someone picking up a fresh fall
virtually on impact, like the Portales/plastic contact
would have to have been, is highly unlikely. It
seems to me that the uniformity of reports of falls
being cold to the touch, betray the fact that they
have been on terra firma for several seconds or a
minute, surely enough time for the frozen mass to cool
its crust> veneer. Unless a rock were picked up
virtually immediately upon impact, I betcha most of
those reports of them being red-hot are just wishful
thinking and/or sensationalism, like that story of the
one that was "glowing underwater". ;-)
>
> Gregory
>
>
>

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Received on Mon 12 Feb 2001 10:16:54 PM PST