[meteorite-list] First Tunguska Meteorite Fragments Discovered

From: Adam Hupe <*raremeteorites_at_meteoritecentral.com*> Date: Thu, 2 May 2013 08:21:54 -0700 (PDT) Message-ID: <1367508114.79213.YahooMailNeo_at_web122003.mail.ne1.yahoo.com> · raremeteorites_at_meteoritecentral.com

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On 5/2/13, Ron Baalke <baalke at zagami.jpl.nasa.gov> wrote:
>
>
> http://www.technologyreview.com/view/514511/first-tunguska-meteorite-fragments-discovered/
>
> First Tunguska Meteorite Fragments Discovered
> The Physics arXiv Blog
> May 2, 2013
>
> Nobody knows what exploded over Siberia in 1908 but the discovery
> of the first fragments could finally solve the mystery
>
> The Tunguska impact event is one of the great mysteries of modern history.
> The basic facts are well known. On 30 June 1908, a vast and powerful
> explosion engulfed an isolated region of Siberia near the Podkamennaya
> Tunguska River.
>
> The blast was 1000 times more powerful than the bomb dropped on Hiroshima,
> registered 5 on the Richter scale and is thought to have knocked down
> some 80 million trees over an area of 2000 square kilometres. The region
> is so isolated, however, that historians recorded only one death and just
> handful of eyewitness reports from nearby.
>
> But the most mysterious aspect of this explosion is that it left no crater
> and scientists have long argued over what could have caused it.
>
> The generally accepted theory is that the explosion was the result of a
> meteorite or comet exploding in the Earth's atmosphere. That could have
> caused an explosion of this magnitude without leaving a crater. Such an
> event
> would almost certainly have showered the region in fragments of the parent
> body
> but no convincing evidence has ever emerged.
>
> In the 1930s, an expedition to the region led by the Russian mineralogist
> Leonid Kulik returned with a sample of melted glassy rock containing
> bubbles.
> Kulik considered this evidence of an impact event.
>
> But the sample was somehow lost and has never undergone modern analysis.
> As such, there is no current evidence of an impact in the form of
> meteorites.
>
> That changes today with the extraordinary announcement by Andrei Zlobin from
>
> the Russian Academy of Sciences that he has found three rocks from the
> Tunguska region with the telltale characteristics of meteorites. If he
> is right, these rocks could finally help solve once and for all what kind
> of object struck Earth all those years ago.
>
> Zlobin's story is remarkable in a number of ways. The area of greatest
> interest
> for meteor scientists is called the Suslov depression, which lies directly
> beneath
> the location of the air blast and is the place where meteorite debris was
> most
> likely to fall.
>
> Dig into the peat bogs here and you can easily find layers that show clear
> evidence
> of the explosion. Zlobin said he dug more than ten prospect holes in the
> hope of
> finding meteorite fragments, but without success.
>
> However, he had more luck exploring the bed of the local Khushmo River,
> where
> stones are likely to collect over a long period of time. He collected around
> 100
> interesting specimens and returned to Moscow with them.
>
> This expedition took place in 1988 and for some unexplained reason, Zlobin
> waited 20
> years to examine his haul in detail. But in 2008, he sorted the collection
> and found
> three stones with clear evidence of melting and regmalypts, thumblike
> impressions
> found on the surface of meteorites which are caused by ablation as the hot
> rock falls
> through the atmosphere at high speed.
>
> Zlobin and others have used tree ring evidence to estimate the temperatures
> that the
> blast created on the ground and says that these were not high enough to melt
> rocks on
> the surface. However, the fireball in the Earth's atmosphere would have been
> hot enough
> for this.
>
> So Zlobin concludes that the rocks must be fragments of whatever body
> collided with
> Earth that day.
>
> Zlobin has not yet carried out a detailed chemical analysis of the rocks
> that would
> reveal their chemical and isotopic composition. So the world will have to
> wait for this
> to get a better idea of the nature of the body.
>
> However, the stony fragments do not rule out a comet since the nucleus could
> easily
> contain rock fragments, says Zlobin. Indeed he has calculated that the
> density of the
> impactor must have been about 0.6 grams per cubic centimetre, which is about
> the same
> as nucleus of Halley's comet. Zlobin says that together the evidence seems
> "excellent
> confirmation of cometary origin of the Tunguska impact."
>
> Clearly there is more work to be done here, particularly the chemical
> analysis perhaps
> with international cooperation and corroboration.
>
> Then there is also the puzzle of why Zlobin has waited so long to analyse
> his samples.
> It's not hard to imagine that the political changes that engulfed the Soviet
> Union in
> the year after his expedition may have played a role in this, but it still
> requires
> some explaining.
>
> Nevertheless, this has the potential to help clear up one of the outstanding
> mysteries
> of the 20th century and finally determine the origin of the largest Earth
> impact in
> recorded history.
>
> Ref: arxiv.org/abs/1304.8070: Discovery of Probably Tunguska Meteorites at
> the Bottom
> of Khushmo River's Shoal
>
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