[meteorite-list] Fw: [Geology2] Meteorite fragments discovered 20 years after bolide event in Czech Republic

[MEM]

 <www.sciencedaily.com/releases/2014/10/141014142736.htm>

Meteorite fragments discovered 20 years after bolide event in Czech Republic
Date: October 14, 2014
Source: Astronomy & Astrophysics
Summary: Scientists have discovered meteorite fragments 20 years after the corresponding bolide 
was seen in the skies of the Czech Republic. This discovery was made possible by reanalyzing the trajectory, which moved the impact line by 330 meters. Interestingly, the meteorites found on the ground are of 
different types, pointing to a parent asteroid of heterogeneous composition.



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First three Benešov meteorites found in April 2011, with metal detectors. From left to 
right: H5 chondrite of 1.56 g, LL3.5 chondrite of 7.72 g with achondrite clast, and LL3.5 chondrite of 1.99 g [2].
Credit: Image courtesy of Astronomy & Astrophysics


Astronomy & Astrophysics is publishing the spectacular discovery of meteorite fragments 20 years after the corresponding bolide was seen in the skies of the Czech 
Republic. This discovery was made possible by reanalyzing the 
trajectory, which moved the impact line by 330 meters. Interestingly, 
the meteorites found on the ground are of different types, pointing to a parent asteroid of heterogeneous composition.
Collisions of meter-sized meteoroids with Earth's atmosphere are 
relatively rare, occurring about 40 times a year. They cause very 
spectacular events, known as superbolides. One of the best known such 
events, the Benešov bolide, occurred on 7 May 1991 at 23h 03m 46s UT 
over the Czech Republic. It was recorded during systematic photographic 
observations by the European Fireball Network and certainly ended in a 
multiple meteorite fall, but no meteorite was found in the weeks and 
years after the fall, despite many attempts.
In February 2011, nearly 20 years after the event, P. Spurný and his 
colleagues [1] measured the records again and analyzed the data with 
improved methods. This led to a new picture of the whole event with a 
revised atmospheric trajectory and a new impact location. This allowed 
the team to recover the Benešov meteorites, 20 years after the fall, 
exactly in the newly predicted area. It is the first time a meteorite is found so long after the bolide observation.
The team found four small, highly-weathered meteorites with a total 
mass of 12 g. The probability that these four fragments come from 
different meteoroids and were found by chance at the same place is 
estimated to be 1 in 100,000 or less. Even more interestingly, these 
four meteorites are of three different mineralogical types. This means 
that the Benešov meteoroid was heterogeneous and contained at least 
three different types of material. After the Almahata Sitta fall, this 
is the second time that such a heterogeneous composition has been found. It raises the possibility that a significant fraction of all asteroids 
are heterogeneous and that they were strongly reprocessed by collisions 
with other asteroids in the main belt.
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Story Source:
The above story is based on materials provided by Astronomy & Astrophysics. Note: Materials may be edited for content and length.
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Journal Reference:
    1. Pavel Spurný, Jakub Haloda, Jiří Borovička, Lukáš Shrbený, Patricie Halodová. Reanalysis of the Benešov bolide and recovery of polymict breccia meteorites – old mystery solved after 20 years. Astronomy & Astrophysics, 2014; 570: A39 DOI: 10.1051/0004-6361/201424308 
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Astronomy & Astrophysics. "Meteorite fragments discovered 20 years after 
bolide event in Czech Republic." ScienceDaily. ScienceDaily, 14 October 
2014. <www.sciencedaily.com/releases/2014/10/141014142736.htm>.



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