Since, from the whole Earth, only 33 rich in olivine silicates (Greenberg and -finds (and 2 falls) have been Chapman, 1984). Following the as­ Tentative Time-table described, this is a strong indication that teroid's colling, the top layer of silicates the new specimens are part of the well­ may have been stripped off, exposing of Council Sessions known fall. the now contracted and cracked Pallasi­ and Committee Meetings The site of the old crater-like excava­ tic layer to erosion. for First Half of 1987 tion was also visited. In the 'splinters The asteroidal origin could, in princi­ May 18 area' about 1 kg of minor fragments (0.1 pie be ascertained by orbital calculation Users Committee May 19 Scientific Technical to approximately 250 grammes were of falls. This has been done on Committee collected. A few particles were found up three occasions (the falls at Pffbram, May 20-21 Finance Committee to 1,000 m north-east of the 'crater'. Lost City, Innisfree) but none of the May 26-27 Observing Pro­ Otherwise, we can confirm Buchwald's in question were . grammes Committee, statements as to the shape and extent Ground-based observations may Venice of the area. We estimate that it still holds nevertheless help solving the question. June 3 Committee 01 Coun­ of the order of 1,000 kg of meteoritic By infrared spectroscopy three candi­ eil, Bruges . date parent- have been found: June 4 Council, Bruges 246 Asporina, 289 Nenetta, 446 Aeter­ All meetings will take place at ESO in nitas (Cruikshank and Hartmann, 1984, Garehing unless stated otherwise. The Imilac Strewn-Field Scott, 1984). Their spectra show an ab­ The existence of the splinters area sorption band at 1.06 l-lm, as does indicates that a large chunk of the olivine in its meteoritic form. Also the References meteorite suffered a violent break-up. general trend of the spectra is consis­ This must have happened at a late point tent with the presence of a metallic Buchwald, V. F., 1975, Handbook of lron of the trajectory through the atmo­ phase. Meteorites, University of California press, sphere. Its mass exceeded, by far, those It is rare that asteroids can be associ­ Berkeley, vol. 1-3. which fell further to the south-west. ated with one particular type of mineral. Cruikshank, D. P., and Hartmann, W. K., Therefore, it seems likely that the parent Detailed studies of asteroids and com­ 1984, Seienee 223,281. body arrived from south-west, rather ets will, in general, require spacecraft to Greenberg, R., and Chapman, C. R., 1984, learus, 57, 267. than opposite. The splinters area is ap­ do "sample-return" missions. Such are, Nininger, H. H., 1952, Out of the Sky, Dover, proximately aligned with the new find in fact, being considered. But perhaps it New York. locations, giving a further argument for is superfluous to include Asporina, Peck, E., 1979, Sky and Teleseope, 58, their association. Measured from north Nenetta or Aeternitas in the itinerary: the p.126. over east, the azimuth of the combined stuff may already be in our hands ... Scott, E. R. D., Nature, 311, 708. strewn-field is 47°+/-3°. The new finds show that the strewn­ field is at least 8 km long and about 1 km wide. It cannot be excluded that Pallasite Meteorites the nearby 3.5-km diameter Steinheim Ba­ some of the meteorites collected a long sin. There is geologieal evidenee that both Meteorites ean be divided into three clas­ time aga were found in the 'new' area. are meteoritie, but the proof (meteoritie ses: Stones, , and Stony Irons. A sub­ We did, in fact, notice a small number of materialj is not yet found. It may long sinee group of the latter is quite peeuliar: an iron/ minor holes from where it is conceivable have weathered away. mixture forms a sponge-like strue­ that specimens (in the 1O-kg class) have ture. Olivine erystals, of eross-seetion 1 to been picked up. Indications are that the 10 mm fill out the holes, so that the volume Strewn-fields strewn-field is even longer than men­ ratio metal/olivine is about 1 : 1. The first tioned. This topic, and other aspects of such meteorite was found in 1771/72 by the The hyper-sonie velocity, 15 to 72 km/ the Imilac fall, are discussed in a forth­ German explorer Peter Simon Pallas, dur­ sec, with whieh meteorites enter the Earth's coming thesis work by E. Martfnez, Uni­ ing his travels through East Russia. Palla­ atmosphere, ereates a shoek, whieh offen versidad dei Norte. The total weight of site meteorites are quite rare: less than 1 forees the meteorite to break up. Masses less than a few tons will reaeh the ground recovered material is now about 560 kg. per cent of all falls and 3.5 per cent of all finds belong to this group. with sub-sonie speed, 100-300 metres per To this adds the estimated 1,000 kg of seeond. Small partieles tend to fall along small meteorite particles stillieft in the Meteorite Craters steeper trajeetories than heavier ones. This top-soil. Although impressive, at least ereates a eharaeteristie elliptie distribution one other Pallasite find is larger. That at Upon hitting the ground, a large meteor­ pattern, with partiele size inereasing along , USA, had a mass of 4.5 tons ite may form a erater. If the terminal velocity the major axis, in the direetion of flight. This (Nininger, 1957, Peck, 1979). It too is suffieiently high, the eonversion ofkinetie simple pieture holds, if just one event of suffered violent fragmentation. energy will lead to the meteorite's instan­ fragmentation took plaee. Strewn-fields taneous evaporation. An explosion erater is ean reaeh eonsiderable sizes. The Gibeon­ thereby formed. Smaller masses may form fall at South-West Afriea eovered approxi­ Asteroidal Origin for Pallasites impact eraters. 13 genuine meteor eraters mately 100 by 400 km. (or erater fjelds) are known and some 100 Pallasite meteorites form a rather others are eonsidered probable. The largest homogeneous group, clearly distinct is the meteorite erater in Arizona, USA, Meteorite Collections from the other type of stony-irons, the whieh has a diameter of 1,200 metres. Third Colleetions of meteorites exist at many . They may hold clues to on the list is the more than 100,000-year museums. Prominent between these are the origin of solar-system bodies. Their old, 370-m diameter erater at Monturaqui. the museums of natural history in London, creation is therefore a much debated This is only 60 km from the loeation men­ Paris, Vienna, and the Aeademy of Sei­ issue between 'cosmogonists'. One tioned in the artiele, but unrelated. Euro­ enees, Moseow. The heaviest meteorite on pean probable meteorite eraters inelude the theory says that they formed in as­ display in Europe is 'Agpalilik', a 14-ton iron 15-million-year-old, 27-km-diameter Nörd• from Greenland, now at the Geologieal teroids, at the interface between a mol­ linger Ries strueture in West Germany and Museum, Copenhagen. ten core and a partially molten mantle,

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