Meteorites - WHAT DO METEORITES TELL US ABOUT THE ORIGIN OF...

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WHAT DO METEORITES TELL US ABOUT THE ORIGIN OF THE SOLAR SYSTEM? THE ANSWER IS THAT METEORITES TELL US ABOUT FOUR(4) PRINCIPAL ASPECTS, in a certain amount of detail – we will look at some key points: (i). PRE-SOLAR AND EARLY SOLAR SYSTEM COMPONENTS. (ii). COMPOSITIONAL INFORMATION i.e. CHEMISTRY. (iii). A VARIETY OF PROCESSES. (iv). ABSOLUTE TIME, AND ABSOLUTE TIMING OF EARLY SOLAR SYSTEM PROCESSES – which can be compared with proplyd and circumstellar disc timing estimates, amongst other things, to check for consistency and possible generalisations. BUT FIRST, WE SHOULD LOOK AT A NUMBER OF INTRODUCTORY POINTS.
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TOTAL NUMBER OF METEORITES THE POTENTIAL DATABASE – is it large/is it small? McSWEEN (1999 – “The New Solar System”; p. 353) GIVES THE FOLLOWING INFORMATION, AS OF 1997, excluding multiple samples of the same meteorite: (i). FALLS1 – i.e. meteorites observed to fall…………………………933 (ii). FINDS1 – i.e. just found; no observed fall……………………….2,487 (iii). ANTARCTIC FINDS – following the first discovery in 1969…. .8,982 1NON-ANTARCTIC. FOR A GRAND TOTAL OF: ~ 12,402 – so the potential database is pretty good, and continues to grow from continued Antarctic and desert searches. NOTE: (i). ~70% OF THE TOTAL ARE ANTARCTIC FINDS. (ii). ~30% OF THE NON-ANTARCTIC METEORITES ARE “FALLS”. (iii). THIS TOTAL INCLUDES, as of 1997: 14 MOON – DERIVED SAMPLES – the first was ID’ed in 1982/83. 13 MARS – DERIVED SAMPLES – now 16(Science,24 Nov., 2000,p. 1465). (iv). ALL THE REST, subject to new identifications, ARE PRINCIPALLY MAIN BELT ASTEROID SAMPLES WHICH BECAME NEA’s PRIOR TO INTERSECTION WITH EARTH’S ORBIT. (v). McSWEEN’S 1997 TOTAL OF 12,402 COMPARES WITH A TOTAL GIVEN IN A 4 FEB., 2000 NOTE IN “SCIENCE”(p. 763) OF ~20,000 – presumably multiple samples of the same meteorite and new finds account for the rather large difference.
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METEORITE TYPES AND RELATIONS WITH ASTEROID TYPES THE PRIMARY AND HISTORICAL SUBDIVISION IS THREEFOLD: (i). “STONES”, (ii). “IRONS”, and (iii). “STONY-IRONS”. THE “STONES” CONSIST PRIMARILY OF SILICATE – OXIDE – METAL MINERALS +/-CARBONACEOUS MATERIAL, THE “IRONS” CONSIST PRIMARILY OF Fe – Ni METAL PHASES, AND THE “STONYIRONS” ARE MIXTURES OF THE ABOVE (and contain some particularly beautiful meteorites called PALLASITES – visit the ROM.
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Chondrites THE “STONES” ARE SUB-DIVIDED IN A VERY IMPORTANT WAY INTO THOSE THAT DO, AND THOSE DON’T, CONTAIN A SIGNIFICANT FEATURE: Approximately spherical, ~0.5-5 mm “CHONDRULES”, named after the Greek word for “seed” (chondros) in 1864. CONTAIN………………CHONDRITES. DON’T CONTAIN……. . ‘A’CHONDRITES. (i). “STONES” – CHONDRITES: BY FAR THE MOST ABUNDANT TYPE OF FALL, and therefore
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Meteorites - WHAT DO METEORITES TELL US ABOUT THE ORIGIN OF...

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