A&A Article: Discovery of the Benešov meteorites

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A&A Article: Discovery of the Benešov meteorites

Postby David Entwistle » Wed Oct 15, 2014 1:10 am

I see that the journal Astronomy & Astrophysics have a press release: Discovery of the Benešov meteorites 20 years after the bolide event.

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 the 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.


Benesov.jpg
Benešov Meteorites
Benesov.jpg (32.48 KiB) Viewed 5067 times


The meteorites were recovered in 2011 and there details are at the links below.


The full paper is available at the following link.

Reanalysis of the Benešov bolide and recovery of polymict breccia meteorites – old mystery solved after 20 years by P. Spurny, J. Haloda, J. Borovicka, L. Shrbeny, P. Halodova.

Abstract
The main motivation for this work was to explain and solve the old mystery connected with the detailed instrumental observation of the Benešov superbolide on 7 May 1991 over the central part of the Czech Republic. Detailed analyses of this undoubted meteorite fall were published in several papers, and this is one of the best documented bolides (at least of the superbolide category) ever observed. However, despite high-quality data, favorable trajectory, relatively large terminal mass, and especially great efforts and many attempts, no meteorite was found in the weeks and years after the fall. Here we solve and explain this old mystery. In spring 2011, just before the twentieth anniversary of this extraordinary case, we remeasured all available all-sky records and reanalyzed the data. We used slightly different methods and new approaches, which we gradually developed to analyze several recent instrumentally observed meteorite falls (Morávka, Neuschwanstein, Jesenice, Bunburra Rockhole, Mason Gully, and Košice). We assembled a new consistent picture of the Benešov event, which resulted in a slightly revised impact location and suggested a new strategy that might lead to a recovery of Benešov meteorites after 20 years. The reality completely confirmed all our assumptions and surpassed our expectations. We found four small highly weathered fragments irregular in form and completely without fusion crust with a total mass of 11.63 g (1.54 g (H5), 7.72 g (with achondritic clast), 1.99 g, 0.38 g (all LL3.5)). They were recovered exactly in the predicted impact area for corresponding masses, namely within 40 m from the highest probability line. Although all fragments are very small and their weathering grade is high (W3 for all pieces), their interior was preserved enough for reliable analysis (except for the smallest one). The meteorite is classified as a polymict breccia containing three recognized lithologies with different texture, chemical, and mineralogical composition. This result is pioneering in many aspects. We proved that in some special cases it is still possible to predict and find meteorites a long time after the fall. The most important result, however, is the heterogeneity of the recovered meteorites. This case clearly shows that larger meteoroids can be compositionally very complicated bodies. We discovered that the Benešov meteoroid consisted of at least three different types of material – LL3.5, H5, and primitive achondrite. This case also implies that it is very useful to study as many fragments as possible from one fall because there can be significant differences among them.
David Entwistle
 
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