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Re: (meteorobs) Excerpts from "CCNet 123/2001 - 22 November 2001"
In a message dated 12/6/01 3:36:11 PM Eastern Standard Time,
l.stachowicz@btinternet.com writes:
<< Just thought i might add - a graphic demonstration of how fragile cometary
material is,was the Tunguska event of 1908 where a cometary fragment exploded
when it entered the atmosphere. As far as i know,despite this being a large
meteor,no meteorites were ever recovered.
On June 30th, 1908, *something* exploded 8 km high on the river Stony
Tunguska, destroying about 2150 square kilometre of Siberian taigà.
Tunguska's seismic tremors caused by the blast were picked up 893 kilometres
away at the Irkutsk Magnetic and Meteorological Station. About 45 minutes
later the same meteorological station recorded the passage of the blast wave.
Thats a far cry from some "space stones" ending up in someones backyard.
<< It's generally accepted that the fragment belonged to the Taurid meteoroid
stream,... >>
What ever hit Tunguska I feel was hardly a fragment of the Taurid meteroid.
This would have to be a comet or a large part of a comet (Encke maybe?) or a
low density asteroid such as Matilda.
<< ... and the meteors which enter the atmosphere have a substantially lower
entry velocity compared to Leonids,which would make them more lightly to
survive the journey to the ground -and yet none were recovered (although
there is still the possibility that currently undiscovered fragments did
make it to the ground)! >>
As per the Tunguska Meeting of 2001, nothing as been recovered.
<<Having said all that i will now contradict myself,and site the more recent
case of the Tagish Lake Meteorite (January 18 2000) which was also
attributed to a cometary fragment. Although it also exploded after entering
the atmosphere,some fragments were recovered,well preserved from the frozen
surface of the lake. So i guess cometary material can survive intact,albeit
exceptionally rare! >>
From my readings, Tagish Lake not comet debris but a chunk of asteroid. It
was classified as a carbonaceous chondrite.
These quotes are from the Meteorite Studies web site:
". After calculating an orbit for this meteoroid [Tagish Lake], the aphelion
was found to lie in the outer asteroid belt, possibly associated with the
Apollo asteroid group; in particular, the low-albedo D type asteroids. "
"It is spectrally most similar to the D-class asteroids located in the outer
belt region, the first such match ever made to this asteroid class. Among the
D-class asteroids with similar spectra to Tagish Lake, 368 Haidea provides
the best match. "
<<Both of the examples I've given are of events much larger than "standard"
Leonid fireballs,but i guess the same principals would apply ??? >>
Larger? I would say so - I think we're trying to compare apples and oranges
here. A "typical" Leonid particle is guessitmated to be the size of a grain
of sand or smaller.
Tagish Lake was estimated to have been ~6 m (~18 ft.) in diameter with a
preatmospheric weight of ~200,000 kg, approached at ~16 kilometers per second
and exploded at an altitude of 25 km with an energy equivalent to 5 kilotons
of TNT.
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