To: WSFAlist at WSFA.org
Date: Mon, 14 Jun 2004 04:32:45 -0400
Subject: [WSFA] Re: meteorite question
From: ronkean at juno.com
Reply-To: WSFA members <WSFAlist at WSFA.org>

On Mon, 14 Jun 2004 00:00:40 -0400 "Ted White" <twhite8 at cox.net> writes:

> I find it astonishing that any meteorite's flaming trip through our
> atmosphere would leave it *needing* to be dried out in an oven.
>

At first thought, yes.  But now it occurs to me that a meteorite could
land in a wet condition if it were raining at the time it fell to earth.
Perhaps the experts advise drying a freshly fallen meteorite to arrest
any chemical action which might occur while the meteorite was wet, and to
avoid having contaminants wick into the interior of the meteorite,
carried by the water.  Indeed, even if it were not raining on the ground
at the time, it is conceivable that a meteorite could pick up some
moisture while passing through the atmosphere, if the meteorite were cool
enough to not boil it off before reaching the ground.  Perhaps meteors in
a given range of size and density can cool off while passing through the
cold air a few miles above sea level.  I have heard of a few instances of
meteorites striking and penetrating houses, but I don't recall it being
noted that such meteorites were very hot, or started fires.

The meteorite was 'grapefruit sized', weighing 1.3 kg.  Assuming the
object was a sphere of 6 cm radius, it would have a density of about
1.44, which seems low, for a stony meteorite, and way too low for a
metallic (iron-nickel) meteorite.  Working it another way, assuming a
density of 2.5 for a stony meteorite, the radius would be 5 cm, and that
is just barely consistent with it being 'grapefruit sized'.

Assuming a sphere of 5 cm radius and a density or 2.5, per

http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html#c5

the terminal velocity would be about 71 meters per second or 159 miles
per hour.  It doesn't seem very likely that a 3 pound rock falling at 159
miles per hour would penetrate a typical plywood roof deck, so perhaps
meteorites of that size and weight usually hit the earth at considerably
more than terminal velocity.  In one case I heard of, a meteorite passed
completely through a house and was recovered in the crawlspace underneath
the house.

Ron Kean

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