Free Astronomy Magazine November-December 2014

SMALL BODIES an height of 31 km above the Benešov region down to ground level (we re- mind that the fall was almost vertical with an angle of just 9 degrees, and add that the main explo- sion occurred at an altitude of about 24,400 metres). Also 20 years before the researchers (some the same taking part to the new study) had considered the in- fluence of the wind, but applied it only to the hypothetical more massive fragments −hence less subject to air masses move- ment− and used only 1/3rd of the mea- surements considered in 2011. The new cal- culations show that during the 7 minutes fall, fragments whose weight is between 5 and 10 grams should be deviated from the ideal trajectory by some 2.5 km towards East-North-East. By overlaying the new location on Google Earth/Maps, the re- searchers realized that many of these frag- ments had surely fallen on a farming area used for growing wheat and corn, and more precisely in a field recently sown and perfectly level- led. Looking for small meteorites the size of pebbles in a field that from the time of the bolide may have been turned over dozens of times might not seem like a good idea, but Spurný’s team considered that the breaking up of the usual 40-50 cm sur- face soil of the last ploughing has cer- tainly hidden a num- ber of fragments, but it has also unearthed other buried in previous years. And since from the spectra obtained during the event was expected an iron content sufficient to be detected by metal detectors, astrono- mers decided to use them for a targeted search that did not damage the crops (dam- age that, quite rightly, the farmer would not have liked). The first scan of the agricul- tural land took place on 9 April 2011, with the participation of twenty searchers. Of the many potential fragments collected, in the end only two passed all the examina- tions, the first weighing 1.5 grams and the F ragments of the Benešov meteorite, specifi- cally sectioned for laboratory tests. Below, micro- scope images of the complex com- pound of the M2 and M3 samples. The darker chon- drules are clearly discernible. [Spurný et al.]