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Re: Great Siberian Explosion
Dona Ebert schrieb:
> The theory which I find solves the most question is that it was a
> comet which struck the area.
> Does this theory and findings also support the theory that life on
> earth started when comets struck the earth ...
Hello Dona, hello List,
Whereas some scientists believe that a small piece of an asteroid
struck in Siberia, other scientists favor a cometary impact. The
protagonists in this discussion were Kresak (cometary origin) and
Sekanina (meteoritic origin).
Zdenek Sekanina from Caltech's JPL disagrees with the cometary
hypothesis. He strongly favors a meteoritic origin (S+T Jan 1984, pp.
18/19).
Kresak based his idea on the fact that the June 30 event occurred near
the time of the annual Beta Taurid meteor shower has long been thought
to derive from comet ENCKE.
... a fragment of Comet ENCKE, separated from it thousands of years ago.
The Beta Taurid meteor shower has a radiant only 10° from the Tunguska
object's radiant.
Here are some of their opposing views:
Points in favor of a cometary origin (Kresak):
(1) no trace of itself -> low mechanical strength and density ->
fragmented and brought to a halt before hitting the ground
(2) vaporization of its ices -> tremendous explosion -> only airborne
dust
(3) skyglows (cometary dust)
(4) Nearness of the Tunguska event to the time of the Beta Taurid meteor
shower
(5) The Beta Taurid meteor shower is thought to derive from Comet ENCKE
(6) The Beta Taurid meteor shower’s radiant is only 10° from the
Tunguska object’s radiant
(7) energy comparable to that expended in forming Meteor Crater but no
sizable crater was formed - this favors a low-density impacting body
(8) the radiant position of the Tunguska object is uncertain to at least
10°
(9) observed ozone depletion at the time about 30% which was caused by
NO
Points in favor of a meteoritic origin (Sekanina)
(1) the majority of evidence points to only one explosion - so no
fragmentation earlier in its flight
(2) the sheer magnitude of the blast argues against an early breakup,
which would have dissipated energy
(3) the bolide remained intact down to a height of only 8.5 km
(4) a fragment of cometary material could not have survived a plunge
into the lower atmosphere
(5) the resistance of the air at a height of 8.5 km is 1000 times as
strong as is necessary for the destruction of a comet entering the
atmosphere at a speed of 26 km/s which is normal for comets
(6) ca. 6 km to the northwest of the "central impact point", there are
two circular lakes - diameter about 100 m.
(7) favorable position of the Tunguska object in the evening sky for
several weeks before the encounter - a comet should have been
discovered
(8) Statistics of observed comets seem to indicate that there are no
active objects with nuclear diameters as small as a hundred meters
(9) from the breakup height the object was not traveling much more than
11 km/s when it entered the atmosphere
(10) the object's farthest aphelion distance of 1 - 1 ½ a.u. is within
the range of short-period comets and asteroids but the Tunguska object
has no perihelion or aphelion near the orbital plane of Jupiter
(11) microscopic spheres of metal and glass were sifted from the soil in
the late 1950's and early 1960's
(12) Soviet researchers found abnormal concentrations of nickel in the
samples, indicative of meteoritic origin
(13) New Jersey researcher Ganapathy discovered enrichments of iridium,
which is cosmically abundant but rare on Earth.
Best wishes,
Bernd
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