MadSci Network: Astronomy |
Hello, Ryan! Positive meteorite origin identification can be done in some cases, but not necessarily in others. For example, some meteorites have included gas compositions that match the isotopic ratios found in the Martian atmosphere, thus strongly implying they were blasted off of Mars during an impact event. This metorite has had analysis done on it; see http://www.campometeorites.com/history.htm. Here's a quote from that site: "The cosmic radiation age was found to be ~14 million years, which is very low compared to other odtahedrites (Nyquiest et al. 1967). "Perry (1944) presented several photomicrographs; one of them (plate 48) undoubtedly show cliftonite, a graphite crystal aggregate, and troilite as stated in the text. Curvello's (1958: 40) application of the aragonite twinning law in this supposedly troilite crystal is therefore invalid. Park et al. (1966) discussed some millimeter-sized silicate inclusions and showed that they consisted of forsterite, chrome diopside, enstatite and oligoclase, decreasing in frequency in that order, and further identified chromite, graphite, troilite and sphalerite, mostly in complex intergrowths. One of the first publications on dislocations in meteorites by thin-film transmission electron microscopy showed that Campo del Cielo had an immobile dislocation network of high density (Ashbee & Vassamillet 1966). Bunch & Cassidy (1968) discussed the numerous deformation structures and found one fragment in particular with indications of heavy plastic flow and recrystallized kamacite. Clarke & Jarosewich (1969) reported a number of excellent analyses (6.7% Ni), the first to be made since the misleading ones performed generations earlier and showing only 5.15.9% Ni (Cohen 1898a; Duclous 1929). Reed (1965; 1969) found 6.26.6% Ni and 670 ppm P in the kamacite. "In 1966, the 1,998 kg El Taco mass was cut in the Max Planck Institut, Mainz. The critical process of making such a large section (about 110 x 40 cm) was carried out under the direction of Professor H. Hintenberger, using a combination of close parallel 1.2 inch drilling holes and sawing. Two slices were prepared. "Nyquist et al (1967), Hintenberger et al (1969) and Schultz et al (1971) determined the rare gases, while Mason (1967) gave a photograph of the newly cut El Taco specimen and discussed the silicate inclusions of iron meteorites in general. Wlotzka & Jarosewich (1969) examined the silicate inclusions in detail. Podosek (1971) presented the argon analyses on a silicate inclusion, and potassium ages calculated by the 40Ar 39Ar method. He estimated a KAr age of 4.6 x 10(9) years and found evidence of a later heating event 3.4 x 10(9) years ago." Since no one doing the analyses seems to have determined an exact origin, we can suppose that the evidence here does not support one. My best guess is that this was a fragment from the interior of a larger body that suffered a collision some 14 million years ago (thus explaining the cosmic radiation age), and that body's composition implies (my personal guess, not a fact) it is from the asteroid belt between Mars and Jupiter. You may wish to get the book "From Stone to Star" by Claude Allegre, which contains within it a whole lot of interesting information on meteroite analysis and how it is done.
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