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Re: (meteorobs) Meteorites and Terminal velocity

GeoZay wrote:

Subject: (meteorobs) Meteorites and Terminal velocity


>
> There was a recent discussion about meteorites heating up during the free
> fall phase of dark flight. Last night while watching the History Channel,
> there was a segment about Joe Kittinger jumping from a balloon at an
altitude
> of 20 miles. His velocity during the free fall reached over 700 mph before
> reaching the denser part of the atmosphere with a slower terminal
velocity.
> His free fall lasted over 4 minutes and 30 seconds. Apparently his fall
> didn't generate enough heat to damage his fragile human body. It wasn't
> mentioned, but I believe I read somewhere else that he lost a glove on his
> way up and suffered frost bite on a part of his exposed hand. I haven't
come
> across anything yet to indicate that he was hot to the touch upon landing
> either. Although Joe isn't a meteorite, it should give some idea about
what
> temperatures a meteorite can expect to produce during free fall.
> GeoZay

 George:
    Your comparison is not the same thing at all.  With a meteoroid, maximum
deceleration takes place in a region from 50 km to around 10 km.  (Your
ballon jumper jumped from over twice the altitude, where ablation stops, and
at zero velocity until gravity accelerated him)  Ablation ceases at around 3
km/sec (6750 mph) and the meteoroid in most cases will cease to be luminous.
At such a high supersonic velocity friction heating is still be taking
place.  The SR-71 does not come close to that velocity and its skin
temperature is not cold as you seem to suggest.  When the meteoroid drops
below subsonic velocity cooling can take place but cooling will be time
dependent on the duration of this subsonic fall.  Meteorites can thus be
cold or warm at impact depending on this time.  Dr. Ian Halliday
investigated the Abee meteorite fall and he reported that this meteorite was
visable as a red glow, down to an altitude of around 1.6 km above sea level.
Dr. Peter Millman investigated the Benton, N.B. fall which was picked up
immediately after landing and this meteorite was hot.  It was reported to be
like a hot potato that you couldn't hold comfortably in your hand but could
toss it from one hand to another.  Other meteorites are cold on landing.
Dr. Halliday refered me to a paper with the title, "Temperatures of
Meteoroids in Space" by Clay P. Butler from the U.S, Naval Radiological
Defence Laboratory in San Francisco, which was published in the Journal,
METEORITICS, volume 3, 1966 pages 59-70.  Meteoroids in a near Earth
enviroment aren't as cold as one would think.
    Believe what you like George, but I think I will accept what the
professionals say until observational evidence indicates otherwise.

Ed Majden


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