[meteorite-list] Re: Tektites III (Short)

From: Kelly Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:32 2004
Message-ID: <3B53C954.8A457A26_at_bhil.com>

Hi, Steve and All,

    This really will be short.

    a) K. P. Florensky (1963) and I. T. Zotkin and M. A. Tsikulin (1966)
reconstructed the airburst height of the Tunguska object as 5000 meters,
or about 3 miles. I can't give the titles; they're in Russian. Terminal
velocity at which cascade fragmentation and airburst occurred: about
3350 meters/second. Dynamic pressure: about 200 kilograms per square
centimenter. If the whatever it was had been just a little heavier
(denser or fatter) or could have taken a little more dynamic pressure,
there would been one helluva hole in Siberia.
    The Russians seem to be very lucky this last century. Shikote-Alin
broke up at the last minute, too.

    b) "Comet Linear C/2000 A2... broke up under the influence of solar
wind pressure, and as it heated up. Comet Kehotek (sp) did the same."
The suggestion that solar wind pressure broke up these comets is unique
to you as far as I can tell. The heating of volatiles and the resultant
gaseous evisceration of the nucleus is the excepted explanation for the
breakup of comets rounding the Sun. Solar wind may possibly be a cause,
but you are introducing a new hypothesis.

    c) "I DID NOT say that they are anywhere as insubstantial as you are
claiming. You have created a "straw man" and are running with it."
    Steve misses the point entirely when he acuses me of creating a
"straw man." My point is that airbursts are only possible when an
impactor cannot penetrate the atmosphere to the surface of the Earth. He
specified a 10 km impactor that airburst, a situation that could only
happen if the impactor had a density less than the atmosphere itself, an
impossibility in a real universe. Above a certain mass, ground impact
must occur.
    The point is that they would have to be that low in density to be
that size and still airburst. The type of this argument is the "reducio
ad absurdum" (lousy spelling) and it means if you take all his claims
together and they imply an absurd result.
    The "math" (really arithmetic) is simple, straightforward, 8th
grade. Now, he says, "solid ice with probably trace or measurable
quantities of dust scattered within," which would imply a density of 0.2
to 1.2 gm/cm^2, or back to a conventional and real-world object which
would penetrate the atmosphere and reach the surface (fail to airburst)
at any size over 160-200 meters or so.

    d) "Your step-by-step density reduction argument is faulty. It has
assumptions that do not take into account the obvious physical nature of
comets. Nor do they take into consideration the fact an object such as
a comet moving at hypersonic velocity will respond in the same way than
a much more solid body such as an asteroid will respond given the same
speed and angle of attack."
    You get so mad, Steve, that you get it turned around. My point was
just that, that they would behave like any object of similar mass and
velocity. I said that over and over again.
    Then, a few pages further on, I say that: "In a sufficiently
energetic event, nothing matters but the raw parameters of energy,"
meaning mass and velocity, and Steve hollers, "WRONG!"
    Which is it, Steve?


    e) See RAHE, VANYSEK, & WEISSMAN, "Properties of Comet Nuclei," in
HAZARDS DUE TO COMETS AND ASTEROIDS, pp. 597-635 on densities,
structural strength, tidal disruption, and fragmentation of comet
impactors. This one selection happens to discuss most of the issues
about comets you have raised. The minimum strength of the comet body can
be estimated from their rotation periods (too weak and they fly apart).
They discuss the fragmentation of comets, which they attribute to
heating, and which only occurs in 1% of short period comets and 4% of
long period comets. The discuss how far apart the fragments of a comet
that breaks up on the way down can fall from each other (the craters are
so close that they overlap or are inside each other).

    f) True, trinitite was not formed in the exact conditions of
tektites, but the sand at and around the base of the blast tower was in
physical contact with a little patch of the universe whose thermometer
suddenly read 30,000,000 degrees that July dawn! If that won't create a
tektite, just how energetic do we have to get? (The glasses from 15
megaton boosted fission bombs don't look like tektites either.)

    g) Far easier to build pyramids that make tektites.

    h) "Just because a cosmic body has such and such a mass DOES NOT
mean that when it hits our atmosphere it will also hit the ground."
    I really hate to disappoint you, Steve, but that's exactly what it
means. Above a certain mass, it's inevitable.
    But look, you are not going to take my word for it; I can tell that.
Why don't you just take the question to someone whose knowledge you
trust and ask them?

Sterling K. Webb
Received on Tue 17 Jul 2001 01:12:54 AM PDT