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RE: (meteorobs) Fwd: Meteorite said to start backyard fire
Continuing along this thread...
I'll bet there are several readers who know enough math to do the
calculations (or have ALREADY done the calculations and just expect folks
like me to look it up!). I haven't the time to punch the numbers, but I'm
curious if all the variables have been accounted for.
This morning I quickly did a little back-of-the-envelope (or post-it note in
my case) calculation for the terminal velocity of an impactor. It seems Lew
is right in saying it's between 200-500 miles/hr for iron meteorites between
baseball and boulder size, slower for the lighter carbon or stony types. If
I had the time and the data in front of me, I'd love to double-check the
altitude that the meteor is slowed to this velocity. (<-- this being the
real point in question as to the temperature of the meteorite!) The height
will vary with entry angle, but at least we could get a range to see if it's
possible for the impactor to be hot.
GeoZay and all, the SR-71 and other supersonic jets do have to deal with
frictional heating. In fact, the SR-71 is limited in velocity BECAUSE of
the heating of the wings, windshield, tail, etc. Pilots do not fly it over
2100 MPH except in certain conditions, but it could theoretically go over
4100 MPH if heat and vibrations were not a factor. When authorized by the
Commander, crews are allowed to go over Mach 3.2 if the skin temperature
does not exceed 427 degrees C. In fact, to properly track an SR-71, you
wouldn't use radar, you'd use infrared detectors.
This velocity is far below the 25,000 to 150,000 MPH that meteors can
achieve, but meteors only have this velocity in our atmosphere for a short
time. How high they are off the ground when their velocity drops below the
frictional heating point will determine if they can reach the ground still
hot.
As I said, if someone has done the pencil pushing I'd love to see it. In
the meantime, I hope someone who has better data than I do can provide us
some more information!
--Terry Johnson
www.rcenter.org
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