[meteorite-list] hot meteorites

From: Mike Mazur <mazur_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:09 2004
Message-ID: <3A889366.FE362C0E_at_geo.ucalgary.ca>

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 interior 99.9% 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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--
_________________________________
Department of Geology and Geophysics
University of Calgary
2500 University Dr. NW
Calgary, AB T2N 1N4
phone: (403)220-8969
email: mazur_at_geo.ucalgary.ca
URL: http://www.ucalgary.ca/~mjmazur

Received on Mon 12 Feb 2001 08:52:38 PM PST