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(meteorobs) Excerpt from "CCNet, 11 November 1999"




------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 11 November 1999
Date: Thu, 11 Nov 1999 09:59:57 -0500 (EST)

CCNet, 11 November 1999
------------------------------

[...]

(4) SERIOUS DOUBTS ABOUT COMETARY DUST LOADING
    Roy Tucker <tucker@noaodot edu>=20

[...]

========================================================

(4) SERIOUS DOUBTS ABOUT COMETARY DUST LOADING

>From Roy Tucker <tucker@noaodot edu>=20

At 12:32 PM 11/8/99 -0500, this was in CCNet:
=20
    "Actually his interpretation of the evidence is more closely=20
    aligned with the suggestion published by Fred Hoyle and N. Chandra=20
    Wickramasinghe in 1978 that the dinosaur extinction was due not to=20
    a cometary impact but rather to a dose call. The logic is=20
    impeccable. The Earth is a tiny target, so for every strike there=20
    are thousands of close approaches.  For asteroids, only impacts=20
    count. But for comets, a flyby results in our planet passing =20
    through the cometary coma, which can be larger than the Moon's=20
    orbit. In such an event, we would accumulate a mass of dust, which=20
    takes years to settle out of the atmosphere. These crossings must=20
    occur on millennial time scales. (Napier and Wickramasinghe are=20
    currently investigating the climatic effects.)"
=20
Dear Dr. Peiser,
=20
The notion that the passage of the earth through a cometary coma can
deposit sufficient dust in the atmosphere to have significant=20
environmental consequences stretches credulity. A major volcanic=20
eruption can introduce many cubic kilometers of silicate particles into =

the atmosphere, perhaps a volume exceeding the dimensions of the=20
average cometary nucleus. Even if a cometary nucleus consisted entirely =

of silicate dust and was totally disrupted to fill the volume of the=20
coma, the earth would sweep up only a tiny fraction of this material=20
even during a central passage.
=20
Let's assume a twenty kilometer diameter cometary nucleus made entirely =

of densely packed silicate particles with a mass of about 10^19 grams.=20
Let us disperse this material uniformly within a spherical volume with=20
a diameter equal to the moon's orbit. The density of material will be=20
about 2 x 10^13 grams/cubic cm. A cylindrical 'core' with a diameter=20
equal to that of the earth through the center of this spherical volume=20
will contain a total of 2 x 10^16 grams of material. This equal to=20
about 7.4 cubic kilometers of the original comet nucleus.
=20
Mount Pinatubo injected about 5 cubic kilometers of material into the=20
atmosphere and produced some beautiful twilight colors. Krakatau=20
produced 18 cubic kilometers. Long Valley spewed 600 cubic kilometers=20
and the Yellowstone caldera dispersed 2000 cubic kilometers
(http://quake.usgsdot gov/VOLCANOES/LongValley/sizes.html).
=20
I think a little more information is required about their hypothesis.=20
Simple introduction of dust into the atmosphere doesn't seem to be a=20
compelling argument for environmental devastation from the skies.
=20
		Best regards,
		  - Roy Tucker

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